Tsetse ( , or ) (sometimes spelled tzetze; also known as tik-tik flies), are large,
biting flies
Many species of arthropods (insects, arachnids and others) regularly or occasionally bite or sting human beings. Insect saliva contains anticoagulants and enzymes that cause local irritation and allergic reactions. Insect venoms can be delivered b ...
that inhabit much of tropical
Africa
Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...
.
Tsetse flies include all the species in the
genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...
''Glossina'', which are placed in their own family, Glossinidae. The tsetse are
obligate parasite
An obligate parasite or holoparasite is a parasitic organism that cannot complete its life-cycle without exploiting a suitable host. If an obligate parasite cannot obtain a host it will fail to reproduce. This is opposed to a facultative parasite, ...
s, which live by feeding on the
blood
Blood is a body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the cells, and transports metabolic waste products away from those same cells. Blood in the c ...
of
vertebrate
Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, ...
animals. Tsetse have been extensively studied, because of their role in transmitting disease. They have a prominent economic impact in sub-Saharan Africa, as the
biological vectors of
trypanosomes
Trypanosomatida is a group of kinetoplastid excavates distinguished by having only a single flagellum. The name is derived from the Greek ''trypano'' (borer) and ''soma'' (body) because of the corkscrew-like motion of some trypanosomatid species. ...
, causing
human
Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedalism and exceptional cognitive skills due to a large and complex brain. This has enabled the development of advanced tools, culture, ...
and
animal trypanosomiasis
Animal trypanosomiasis, also known as nagana and nagana pest, or sleeping sickness, is a disease of vertebrates. The disease is caused by trypanosomes of several species in the genus ''Trypanosoma'' such as ''Trypanosoma brucei''. ''Trypanosoma ...
. Tsetse are
multivoltine
Voltinism is a term used in biology to indicate the number of broods or generations of an organism in a year. The term is most often applied to insects, and is particularly in use in sericulture, where silkworm varieties vary in their voltinism.
...
and long-lived, typically producing about four broods per year, with up to 31 broods over their lifespans.
Tsetse can be distinguished from other large flies by two easily-observed features: Primarily, tsetse fold their wings over their
abdomen
The abdomen (colloquially called the belly, tummy, midriff, tucky or stomach) is the part of the body between the thorax (chest) and pelvis, in humans and in other vertebrates. The abdomen is the front part of the abdominal segment of the torso. ...
s completely when they are resting (so that one wing rests directly on top of the other); Secondly, tsetse also have a long
proboscis
A proboscis () is an elongated appendage from the head of an animal, either a vertebrate or an invertebrate. In invertebrates, the term usually refers to tubular mouthparts used for feeding and sucking. In vertebrates, a proboscis is an elong ...
, extending directly forward, which is attached by a distinct bulb to the bottom of their heads.
Fossilized
A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved in ...
tsetse have been recovered from
Paleogene
The Paleogene ( ; British English, also spelled Palaeogene or Palæogene; informally Lower Tertiary or Early Tertiary) is a geologic period, geologic period and system that spans 43 million years from the end of the Cretaceous Period million yea ...
-aged rocks in the United States and Germany. Twenty-three extant species of tsetse flies are known from the African continent as well as the Arabian Peninsula.
Etymology
The word ''tsetse'' means "fly" in
Tswana
Tswana may refer to:
* Tswana people, the Bantu speaking people in Botswana, South Africa, Namibia, Zimbabwe, Zambia, and other Southern Africa regions
* Tswana language, the language spoken by the (Ba)Tswana people
* Bophuthatswana, the former ba ...
, a
Bantu language
The Bantu languages (English: , Proto-Bantu: *bantʊ̀) are a large family of languages spoken by the Bantu people of Central, Southern, Eastern africa and Southeast Africa. They form the largest branch of the Southern Bantoid languages.
The t ...
of southern Africa.
Recently, ''tsetse'' without the fly has become more common in
English
English usually refers to:
* English language
* English people
English may also refer to:
Peoples, culture, and language
* ''English'', an adjective for something of, from, or related to England
** English national ide ...
, particularly in the scientific and development communities.
The word is pronounced ''tseh-tseh'' in the
Sotho languages Sotho may refer to:
*Sotho people (or ''Basotho''), an African ethnic group principally resident in South Africa, Lesotho and southern Botswana
*Sotho language (''Sesotho'' or ''Southern Sotho''), a Bantu language spoken in southern Africa, an offi ...
and is easily rendered in other African languages. During World War II, a British
de Havilland
The de Havilland Aircraft Company Limited () was a British aviation manufacturer established in late 1920 by Geoffrey de Havilland at Stag Lane Aerodrome Edgware on the outskirts of north London. Operations were later moved to Hatfield in H ...
antisubmarine aircraft was known as the 'Tsetse'
Mosquito
Mosquitoes (or mosquitos) are members of a group of almost 3,600 species of small flies within the family Culicidae (from the Latin ''culex'' meaning " gnat"). The word "mosquito" (formed by ''mosca'' and diminutive ''-ito'') is Spanish for "li ...
.
Biology
The biology of tsetse is relatively well understood by
entomologists
Entomology () is the scientific study of insects, a branch of zoology. In the past the term "insect" was less specific, and historically the definition of entomology would also include the study of animals in other arthropod groups, such as arach ...
. They have been extensively studied because of their medical, veterinary, and economic importances, because the flies can be raised in a laboratory, and because they are relatively large, facilitating their analysis.
Morphology
Tsetse flies can be seen as independent individuals in three forms: as third-
instar
An instar (, from the Latin '' īnstar'', "form", "likeness") is a developmental stage of arthropods, such as insects, between each moult (''ecdysis''), until sexual maturity is reached. Arthropods must shed the exoskeleton in order to grow or ass ...
larvae, pupae, and adults.
Tsetse first become separate from their mothers during the third larval instar, during which they have the typical appearance of
maggots
A maggot is the larva of a fly (order Diptera); it is applied in particular to the larvae of Brachycera flies, such as houseflies, cheese flies, and blowflies, rather than larvae of the Nematocera, such as mosquitoes and crane flies.
Entomol ...
. However, this life stage is short, lasting at most a few hours, and is almost never observed outside of the laboratory.
Tsetse next develop a hard external case, the puparium, and become pupae - small, hard-shelled oblongs with two distinctively small, dark lobes at the tail (breathing) end. Tsetse pupae are under long.
Within the puparial shell, tsetse complete the last two larval instars and the pupal stage.
At the end of the pupal stage, tsetse emerge as adult flies. The adults are relatively large flies, with lengths of ,
and have a recognizable shape, or
bauplan
A body plan, ( ), or ground plan is a set of morphological features common to many members of a phylum of animals. The vertebrates share one body plan, while invertebrates have many.
This term, usually applied to animals, envisages a "bluepr ...
, which makes them easy to distinguish from other flies. Tsetse have large heads, distinctly separated eyes, and unusual antennae. The
thorax
The thorax or chest is a part of the anatomy of humans, mammals, and other tetrapod animals located between the neck and the abdomen. In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main divisions of the cre ...
is quite large, while the abdomen is wider, rather than elongated, and shorter than the wings.
Four characteristics collectively separate adult tsetse from other kinds of flies:
Anatomy
Like all other
insect
Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body ( head, thorax and abdomen), three pairs ...
s, tsetse flies have an adult body comprising three visibly distinct parts: the head, the thorax and the abdomen.
The head has large eyes, distinctly separated on each side, and a distinct, forward-pointing proboscis attached underneath by a large bulb. The thorax is large, made of three fused segments. Three pairs of legs are attached to the thorax, as are two wings and two
halteres
''Halteres'' (; singular ''halter'' or ''haltere'') (from grc, ἁλτῆρες, weights held in the hands to give an impetus in leaping) are a pair of small club-shaped organs on the body of two orders of flying insects that provide infor ...
. The abdomen is short but wide and changes dramatically in volume during feeding.
![Gándulas de la leche de Glossina](https://upload.wikimedia.org/wikipedia/commons/7/74/G%C3%A1ndulas_de_la_leche_de_Glossina_.gif)
The internal anatomy of the tsetse is fairly typical of the
insect
Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body ( head, thorax and abdomen), three pairs ...
s; the
crop
A crop is a plant that can be grown and harvested extensively for profit or subsistence. When the plants of the same kind are cultivated at one place on a large scale, it is called a crop. Most crops are cultivated in agriculture or hydroponic ...
is large enough to accommodate a huge increase in size during feeding, as tsetse can take a bloodmeal equal in weight to themselves. The
dipteran crop is heavily understudied, with ''Glossina'' being one of the few genera having relatively reliable information available: Moloo and Kutuza 1970 for ''G. brevipalpis'' (including its innervation) and Langley 1965 for ''G. morsitans''.
The reproductive tract of adult females includes a
uterus
The uterus (from Latin ''uterus'', plural ''uteri'') or womb () is the organ in the reproductive system of most female mammals, including humans that accommodates the embryonic and fetal development of one or more embryos until birth. The uter ...
, which can become large enough to hold the third-instar
larva
A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle.
The ...
at the end of each
pregnancy
Pregnancy is the time during which one or more offspring develops ( gestates) inside a woman's uterus (womb). A multiple pregnancy involves more than one offspring, such as with twins.
Pregnancy usually occurs by sexual intercourse, but ca ...
. The article “''
Parasitic flies of domestic animals
Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has ...
''” has a diagram of the anatomy of dipteran flies.
Most tsetse flies are, physically, very tough. Houseflies, and even horseflies, are easily killed with a flyswatter, for example; a great deal of effort is needed to crush a tsetse fly.
Life cycle
![glossina palpalis morsitans](https://upload.wikimedia.org/wikipedia/commons/c/c7/Glossina_palpalis_morsitans.jpg)
Tsetse have an unusual
life cycle
Life cycle, life-cycle, or lifecycle may refer to:
Science and academia
*Biological life cycle, the sequence of life stages that an organism undergoes from birth to reproduction ending with the production of the offspring
*Life-cycle hypothesis, ...
, which may be due to the richness of their blood food source. A female fertilizes only one egg at a time; she will retain each egg within her uterus, the offspring developing internally (during the first three
larval stages), in an adaptation called
adenotrophic viviparity.
During this time, the female feeds the developing offspring with a milky substance (secreted by a modified gland) in the uterus.
In the third larval stage, the tsetse larvae leave the uterus and begin independent life. The newly-birthed larvae crawl into the ground, and develop a hard outer shell (called the
puparial case), within which they complete their morphological transformations into adult flies.
The larval life stage has a variable duration, generally 20 to 30 days, and the larvae must rely on stored resources during this time. The importance of the richness and quality of blood to this stage can be seen; all tsetse development (prior to emerging from the puparial case as a full adult) occurs without feeding, with only the nutrition provided by the mother fly. She must get enough energy for her own survival (in addition to the needs of her developing offspring), as well as for the stored resources which her offspring will require until they emerge as adults.
Technically, these insects undergo the standard
development
Development or developing may refer to:
Arts
*Development hell, when a project is stuck in development
*Filmmaking, development phase, including finance and budgeting
*Development (music), the process thematic material is reshaped
*Photographi ...
process of insects, beginning with
oocyte
An oocyte (, ), oöcyte, or ovocyte is a female gametocyte or germ cell involved in reproduction. In other words, it is an immature ovum, or egg cell. An oocyte is produced in a female fetus in the ovary during female gametogenesis. The female ...
formation, ovulation, fertilization, and development of the egg; following egg development and birth are the three
larva
A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle.
The ...
l stages, a
pupa
A pupa ( la, pupa, "doll"; plural: ''pupae'') is the life stage of some insects undergoing transformation between immature and mature stages. Insects that go through a pupal stage are holometabolous: they go through four distinct stages in their ...
l stage, and the emergence and maturation of the adult.
Hosts
Overall
Suidae
Suidae is a family of artiodactyl mammals which are commonly called pigs, hogs or swine. In addition to numerous fossil species, 18 extant species are currently recognized (or 19 counting domestic pigs and wild boars separately), classified into ...
are the most important hosts. By species, bloodmeals are derived from:
*''
G. swynnertoni'' 6070% from
warthog
''Phacochoerus'' is a genus in the family Suidae, commonly known as warthogs (pronounced ''wart-hog''). They are pigs who live in open and semi-open habitats, even in quite arid regions, in sub-Saharan Africa. The two species were formerly cons ...
, ~8% from
giraffe
The giraffe is a large African hoofed mammal belonging to the genus ''Giraffa''. It is the tallest living terrestrial animal and the largest ruminant on Earth. Traditionally, giraffes were thought to be one species, ''Giraffa camelopardalis ...
*''
G. austeni'' 5060% from
bushpig
:''"Bush pig" may also refer to the red river hog.
The bushpig (''Potamochoerus larvatus'') is a member of the pig family that inhabits forests, woodland, riverine vegetation and cultivated areas in East and Southern Africa. Probably introduced ...
, ~33% from
Bovidae
The Bovidae comprise the biological family of cloven-hoofed, ruminant mammals that includes cattle, bison, buffalo, antelopes, and caprines. A member of this family is called a bovid. With 143 extant species and 300 known extinct species, ...
, possibly 10% from various
duiker
A duiker is a small to medium-sized brown antelope native to sub-Saharan Africa, found in heavily wooded areas. The 22 extant species, including three sometimes considered to be subspecies of the other species, form the subfamily Cephalophina ...
*''
G. fuscipleuris'' 65% from bushpig and
giant forest hog
The giant forest hog (''Hylochoerus meinertzhageni''), the only member of its genus (''Hylochoerus''), is native to wooded habitats in Africa and is generally considered the largest wild member of the pig family, Suidae; however, a few subspecie ...
, up to 20% from
hippopotamus
The hippopotamus ( ; : hippopotamuses or hippopotami; ''Hippopotamus amphibius''), also called the hippo, common hippopotamus, or river hippopotamus, is a large semiaquatic mammal native to sub-Saharan Africa. It is one of only two extan ...
*''
G. tabaniformis'' 70% from
red river hog
The red river hog (''Potamochoerus porcus'') or bushpig (a named also used for the '' Potamochoerus larvatus''), is a wild member of the pig family living in Africa, with most of its distribution in the Guinean and Congolian forests. It is rarel ...
, >7% from
porcupine
Porcupines are large rodents with coats of sharp spines, or quills, that protect them against predation. The term covers two families of animals: the Old World porcupines of family Hystricidae, and the New World porcupines of family, Erethizont ...
s
*''
G. morsitans'' 3045% from warthog, 2540% from various Bovidae, especially
kudu
The kudus are two species of antelope of the genus ''Tragelaphus'':
* Lesser kudu, ''Tragelaphus imberbis'', of eastern Africa
* Greater kudu, ''Tragelaphus strepsiceros'', of eastern and southern Africa
The two species look similar, thou ...
,
buffalo,
bushbuck
The Cape bushbuck (''Tragelaphus sylvaticus'') is a common and a widespread species of antelope in sub-Saharan Africa.Wronski T, Moodley Y. (2009)Bushbuck, harnessed antelope or both? ''Gnusletter'', 28(1):18-19. Bushbuck are found in a wide ra ...
, and
eland
Eland may refer to:
Animals
*''Taurotragus'', a genus of antelope
** Common eland of East and Southern Africa
** Giant eland of Central and Western Africa
Places
* Eland, Wisconsin, United States
* An old spelling of Elland, West Yorkshire
* Ela ...
, most especially
domestic cattle
Cattle (''Bos taurus'') are large, domestication, domesticated, Cloven hoof, cloven-hooved, herbivores. They are a prominent modern member of the subfamily Bovinae and the most widespread species of the genus ''Bos''. Adult females are referr ...
, ~2% from
hartebeest
The hartebeest (; ''Alcelaphus buselaphus''), also known as kongoni or kaama, is an African antelope. It is the only member of the genus ''Alcelaphus''. Eight subspecies have been described, including two sometimes considered to be indepen ...
*''
G. fusca'' 5590% from
bushbuck
The Cape bushbuck (''Tragelaphus sylvaticus'') is a common and a widespread species of antelope in sub-Saharan Africa.Wronski T, Moodley Y. (2009)Bushbuck, harnessed antelope or both? ''Gnusletter'', 28(1):18-19. Bushbuck are found in a wide ra ...
, 15% from red river hog, ~12% from
aardvark
The aardvark ( ; ''Orycteropus afer'') is a medium-sized, burrowing, nocturnal mammal native to Africa. It is the only living species of the order Tubulidentata, although other prehistoric species and genera of Tubulidentata are known. Unlike ...
*''
G. brevipalpis'' up to 40% (high variability with geography) from bushpig, up to 36% from hippopotamus, ~25% from Bovidae, especially buffalo and bushbuck
*''
G. palpalis'' ~3% from wild Suidae, more substantial amounts from
domestic Suidae when available, ~2040% from Bovidae (including domestic cattle) depending on geography, ~10% from waterside birds including
cormorant
Phalacrocoracidae is a family of approximately 40 species of aquatic birds commonly known as cormorants and shags. Several different classifications of the family have been proposed, but in 2021 the IOC adopted a consensus taxonomy of seven ge ...
s, 2530% from ''
Varanus'' and
crocodile
Crocodiles (family (biology), family Crocodylidae) or true crocodiles are large semiaquatic reptiles that live throughout the tropics in Africa, Asia, the Americas and Australia. The term crocodile is sometimes used even more loosely to inclu ...
(possibly higher in natural settings, 50% from crocodile in particular locations)
*''
G. fuscipes'' ~3% from wild Suidae, ~2040% from Bovidae (including domestic cattle) depending on geography, ~10% from waterside birds including
cormorant
Phalacrocoracidae is a family of approximately 40 species of aquatic birds commonly known as cormorants and shags. Several different classifications of the family have been proposed, but in 2021 the IOC adopted a consensus taxonomy of seven ge ...
s, 2530% from ''
Varanus'' and
crocodile
Crocodiles (family (biology), family Crocodylidae) or true crocodiles are large semiaquatic reptiles that live throughout the tropics in Africa, Asia, the Americas and Australia. The term crocodile is sometimes used even more loosely to inclu ...
(possibly higher in natural settings)
*''
G. tachinoides'' ~3% from wild Suidae, more substantial amounts from
domestic Suidae when available, ~2040% from Bovidae (including domestic cattle) depending on geography, >7% from porcupines
*''
G. pallidipes'' 5590% from
bushbuck
The Cape bushbuck (''Tragelaphus sylvaticus'') is a common and a widespread species of antelope in sub-Saharan Africa.Wronski T, Moodley Y. (2009)Bushbuck, harnessed antelope or both? ''Gnusletter'', 28(1):18-19. Bushbuck are found in a wide ra ...
*''
G. longipalpis'' 5590% from
bushbuck
The Cape bushbuck (''Tragelaphus sylvaticus'') is a common and a widespread species of antelope in sub-Saharan Africa.Wronski T, Moodley Y. (2009)Bushbuck, harnessed antelope or both? ''Gnusletter'', 28(1):18-19. Bushbuck are found in a wide ra ...
*''
G. longipennis'' unusually dependant (~60%) on
rhinoceros
A rhinoceros (; ; ), commonly abbreviated to rhino, is a member of any of the five extant species (or numerous extinct species) of odd-toed ungulates in the family Rhinocerotidae. (It can also refer to a member of any of the extinct species o ...
, also ~20% from Bovidae, variably up to 12% from
elephant
Elephants are the largest existing land animals. Three living species are currently recognised: the African bush elephant, the African forest elephant, and the Asian elephant. They are the only surviving members of the family Elephantidae an ...
, up to 7% from
ostrich
Ostriches are large flightless birds of the genus ''Struthio'' in the order Struthioniformes, part of the infra-class Palaeognathae, a diverse group of flightless birds also known as ratites that includes the emus, rheas, and kiwis. There are ...
*''
G. m. submorsitans'' ~6% from various birds excluding ostrich
Waterbuck
The waterbuck (''Kobus ellipsiprymnus'') is a large antelope found widely in sub-Saharan Africa. It is placed in the genus '' Kobus'' of the family Bovidae. It was first described by Irish naturalist William Ogilby in 1833. Its 13 subspecies ar ...
(''Kobus ellipsiprymnus'') are unmolested by ''Glossina''
because they produce
volatiles
Volatiles are the group of chemical elements and chemical compounds that can be readily vaporized. In contrast with volatiles, elements and compounds that are not readily vaporized are known as refractory substances.
On planet Earth, the term ' ...
which act as
repellents. Waterbuck odor volatiles are under testing and development as repellents to protect
livestock
Livestock are the domesticated animals raised in an agricultural setting to provide labor and produce diversified products for consumption such as meat, eggs, milk, fur, leather, and wool. The term is sometimes used to refer solely to animals ...
.
Genetics
The genome of ''Glossina morsitans'' was sequenced in 2014.
Symbionts
Tsetse flies have at least three known bacterial
symbionts
Symbiosis (from Greek , , "living together", from , , "together", and , bíōsis, "living") is any type of a close and long-term biological interaction between two different biological organisms, be it mutualistic, commensalistic, or parasit ...
. The primary symbiont is ''Wigglesworthia'' (''
Wigglesworthia glossinidia
''Wigglesworthia glossinidia'' is a species of gram-negative bacteria which was isolated from the gut of the tsetse fly. ''W. glossinidia'' is a bacterial endosymbiont of the tsetse fly. Because of this relationship, ''Wigglesworthia'' has lost a ...
'') within the fly's
bacteriocyte
A bacteriocyte (Greek for ''bacteria cell''), also known as a mycetocyte, is a specialized adipocyte found primarily in certain insect groups such as aphids, tsetse flies, German cockroaches, weevils. These cells contain endosymbiotic organisms su ...
s, the secondary symbiont is ''Sodalis'' (''
Sodalis glossinidius
''Sodalis glossinidius'' is a species of bacteria, the type and only species of its genus. It is a microaerophilic secondary endosymbiont of the tsetse fly. Strain M1T is the type strain. ''Sodalis glossinidius'' is the only gammaproteobacterial ...
'') intercellularly or intracellularly, and the third is some kind of ''
Wolbachia
''Wolbachia'' is a genus of intracellular bacteria that infects mainly arthropod species, including a high proportion of insects, and also some nematodes. It is one of the most common parasitic microbes, and is possibly the most common reproduct ...
''.
[ ][ ]
Diseases
The
salivary gland hypertrophy virus causes abnormal bleeding in the lobes of the
crop
A crop is a plant that can be grown and harvested extensively for profit or subsistence. When the plants of the same kind are cultivated at one place on a large scale, it is called a crop. Most crops are cultivated in agriculture or hydroponic ...
of ''
G. m. centralis'' and ''
G. m. morsitans''.
Systematics
Tsetse are in the order
Diptera
Flies are insects of the order Diptera, the name being derived from the Greek δι- ''di-'' "two", and πτερόν ''pteron'' "wing". Insects of this order use only a single pair of wings to fly, the hindwings having evolved into advanced ...
, the true flies. They belong to the superfamily Hippoboscoidea, in which the tsetse's family, the Glossinidae, is one of four families of blood-feeding obligate parasites.
Up to 34 species and subspecies of tsetse flies are recognized, depending on the particular classification used.
All current classifications place all the tsetse species in a single genus named ''Glossina''. Most classifications place this genus as the sole member of the family Glossinidae. The Glossinidae are generally placed within the superfamily
Hippoboscoidea
Hippoboscoidea is a superfamily of the Calyptratae. The flies in this superfamily are blood-feeding obligate parasites of their hosts. Four families are often placed here:
* Glossinidae - Tsetse flies
*Hippoboscidae - Ked flies
*Nycteribiidae - B ...
, which contains other
hematophagous
Hematophagy (sometimes spelled haematophagy or hematophagia) is the practice by certain animals of feeding on blood (from the Greek words αἷμα ' "blood" and φαγεῖν ' "to eat"). Since blood is a fluid tissue rich in nutritious pro ...
families.
Species
The tsetse genus is generally split into three groups of species based on a combination of distributional, behavioral, molecular and morphological characteristics.
The genus includes:
* The 'savannah' flies: (subgenus ''Morsitans'', occasionally named ''Glossina''):
** ''
Glossina austeni
Tsetse ( , or ) (sometimes spelled tzetze; also known as tik-tik flies), are large, biting flies that inhabit much of tropical Africa. Tsetse flies include all the species in the genus ''Glossina'', which are placed in their own family, Glo ...
''
( Newstead, 1912) patr. of Austen
** ''
Glossina morsitans
''Glossina morsitans'' is a species of tsetse fly in the genus ''Glossina''. It is one of the major vector (epidemiology), vectors of ''Trypanosoma brucei rhodesiense'' in African savannas.
Taxonomy
''Glossina morsitans'' is variously classified ...
''
(Westwood, 1851)
*** ''
Glossina morsitans submorsitans
Tsetse ( , or ) (sometimes spelled tzetze; also known as tik-tik flies), are large, biting flies that inhabit much of tropical Africa. Tsetse flies include all the species in the genus ''Glossina'', which are placed in their own family, Glos ...
''
** ''
Glossina pallidipes
Tsetse ( , or ) (sometimes spelled tzetze; also known as tik-tik flies), are large, biting flies that inhabit much of tropical Africa. Tsetse flies include all the species in the genus ''Glossina'', which are placed in their own family, Glos ...
''
( Austen, 1903)
** ''
Glossina swynnertoni
Tsetse ( , or ) (sometimes spelled tzetze; also known as tik-tik flies), are large, biting flies that inhabit much of tropical Africa. Tsetse flies include all the species in the genus ''Glossina'', which are placed in their own family, Glo ...
''
( Austen, 1922)GBIF
The Global Biodiversity Information Facility (GBIF) is an international organisation that focuses on making scientific data on biodiversity available via the Internet using web services. The data are provided by many institutions from around the ...
: 5055987 patr. of Swynnerton
Swynnerton is a village and civil parish in Staffordshire, England. It lies in the Borough of Stafford, and at the 2001 census had a population of 4,233, increasing to 4,453 at the 2011 Census.
Swynnerton is listed in the Domesday Book identifyi ...
* The 'forest' flies: (subgenus ''Fusca'', previously named ''Austenia''):
** ''
Glossina fusca fusca''
(Walker, 1849)
** ''
Glossina fuscipleuris
Tsetse ( , or ) (sometimes spelled tzetze; also known as tik-tik flies), are large, biting flies that inhabit much of tropical Africa. Tsetse flies include all the species in the genus ''Glossina'', which are placed in their own family, Glo ...
''
( Austen, 1911)
** ''
Glossina frezili''
(Gouteux, 1987)
** ''
Glossina haningtoni
Tsetse ( , or ) (sometimes spelled tzetze; also known as tik-tik flies), are large, biting flies that inhabit much of tropical Africa. Tsetse flies include all the species in the genus ''Glossina'', which are placed in their own family, Glo ...
''
( Newstead and Evans, 1922)
** ''
Glossina longipennis
Tsetse ( , or ) (sometimes spelled tzetze; also known as tik-tik flies), are large, biting flies that inhabit much of tropical Africa. Tsetse flies include all the species in the genus ''Glossina'', which are placed in their own family, Glo ...
''
(Corti, 1895)
** ''
Glossina medicorum''
( Austen, 1911)
** ''
Glossina nashi''
(Potts, 1955)
** ''
Glossina nigrofusca nigrofusca''
( Newstead, 1911)
** ''
Glossina severini
Tsetse ( , or ) (sometimes spelled tzetze; also known as tik-tik flies), are large, biting flies that inhabit much of tropical Africa. Tsetse flies include all the species in the genus ''Glossina'', which are placed in their own family, Glo ...
''
( Newstead, 1913)
** ''
Glossina schwetzi
Tsetse ( , or ) (sometimes spelled tzetze; also known as tik-tik flies), are large, biting flies that inhabit much of tropical Africa. Tsetse flies include all the species in the genus ''Glossina'', which are placed in their own family, Glos ...
''
( Newstead and Evans, 1921)
** ''
Glossina tabaniformis
Tsetse ( , or ) (sometimes spelled tzetze; also known as tik-tik flies), are large, biting flies that inhabit much of tropical Africa. Tsetse flies include all the species in the genus ''Glossina'', which are placed in their own family, Glo ...
''
(Westwood, 1850)
** ''
Glossina vanhoofi''
(Henrard, 1952)
* The 'riverine' and 'lacustrine' flies: (subgenus ''Palpalis'', previously named ''Nemorhina''):
** ''
Glossina caliginea''
( Austen, 1911)
** ''
Glossina fuscipes
''Glossina fuscipes'' is a riverine fly species in the genus ''Glossina'', which are commonly known as tsetse flies. Typically found in sub-Saharan Africa but with a small Arabian range, ''G. fuscipes'' is a regional vector of African trypanos ...
''
( Newstead, 1911)
*** ''
Glossina fuscipes fuscipes
Tsetse ( , or ) (sometimes spelled tzetze; also known as tik-tik flies), are large, biting flies that inhabit much of tropical Africa. Tsetse flies include all the species in the genus ''Glossina'', which are placed in their own family, Glos ...
''
( Newstead, 1911)
*** ''
Glossina fuscipes martinii''
(Zumpt, 1935)
*** ''
Glossina fuscipes quanzensis
Tsetse ( , or ) (sometimes spelled tzetze; also known as tik-tik flies), are large, biting flies that inhabit much of tropical Africa. Tsetse flies include all the species in the genus ''Glossina'', which are placed in their own family, Glos ...
''
(Pires, 1948)
** ''
Glossina pallicera pallicera''
(Bigot, 1891)
** ''
Glossina pallicera newsteadi
Tsetse ( , or ) (sometimes spelled tzetze; also known as tik-tik flies), are large, biting flies that inhabit much of tropical Africa. Tsetse flies include all the species in the genus ''Glossina'', which are placed in their own family, Glo ...
''
( Austen, 1929) patr. of Newstead
** ''
Glossina palpalis palpalis''
(Robineau-Desvoidy, 1830)
** ''
Glossina palpalis gambiensis
Tsetse ( , or ) (sometimes spelled tzetze; also known as tik-tik flies), are large, biting flies that inhabit much of tropical Africa. Tsetse flies include all the species in the genus ''Glossina'', which are placed in their own family, Glo ...
''
(Vanderplank, 1911)
** ''
Glossina tachinoides
Tsetse ( , or ) (sometimes spelled tzetze; also known as tik-tik flies), are large, biting flies that inhabit much of tropical Africa. Tsetse flies include all the species in the genus ''Glossina'', which are placed in their own family, Glo ...
''
(Westwood, 1850)
Evolutionary history
Fossil glossinids are known from the
Florissant Formation
The Florissant Formation is a sedimentary geologic formation outcropping around Florissant, Teller County, Colorado. The formation is noted for the abundant and exceptionally preserved insect and plant fossils that are found in the mudstones and ...
in North America and the
Enspel Lagerstätte of Germany, dating to the late
Eocene
The Eocene ( ) Epoch is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene' ...
and late
Oligocene
The Oligocene ( ) is a geologic epoch of the Paleogene Period and extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that define the epoch are well identified but the ...
respectively.
Range
''Glossina'' is almost entirely restricted to grassland and forested areas of the
Afrotropics
The Afrotropical realm is one of Earth's eight biogeographic realms. It includes Africa south of the Sahara Desert, the majority of the Arabian Peninsula, the island of Madagascar, southern Iran and extreme southwestern Pakistan, and the island ...
. Only two subspecies - ''
G. f. fuscipes'' and ''
G. m. submorsitans'' - are definitely present in the very southwest of Saudi Arabia. Although Carter found ''
G. tachiniodes'' in 1903 nearby, near
Aden
Aden ( ar, عدن ' Yemeni: ) is a city, and since 2015, the temporary capital of Yemen, near the eastern approach to the Red Sea (the Gulf of Aden), some east of the strait Bab-el-Mandeb. Its population is approximately 800,000 people. ...
in southern Yemen, there have been no confirmations since.
Trypanosomiasis
![Trypanosoma sp](https://upload.wikimedia.org/wikipedia/commons/2/23/Trypanosoma_sp._PHIL_613_lores.jpg)
Tsetse are
biological vectors of
trypanosomes
Trypanosomatida is a group of kinetoplastid excavates distinguished by having only a single flagellum. The name is derived from the Greek ''trypano'' (borer) and ''soma'' (body) because of the corkscrew-like motion of some trypanosomatid species. ...
, meaning that in the process of feeding, they acquire and then transmit small, single-celled trypanosomes from
infected vertebrate
Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, ...
hosts
A host is a person responsible for guests at an event or for providing hospitality during it.
Host may also refer to:
Places
*Host, Pennsylvania, a village in Berks County
People
*Jim Host (born 1937), American businessman
*Michel Host ( ...
to uninfected animals. Some tsetse-transmitted trypanosome species cause
trypanosomiasis
Trypanosomiasis or trypanosomosis is the name of several diseases in vertebrates caused by parasitic protozoan trypanosomes of the genus ''Trypanosoma''. In humans this includes African trypanosomiasis and Chagas disease. A number of other diseas ...
, an infectious disease. In humans, tsetse transmitted trypanosomiasis is called
sleeping sickness
African trypanosomiasis, also known as African sleeping sickness or simply sleeping sickness, is an insect-borne parasitic infection of humans and other animals. It is caused by the species ''Trypanosoma brucei''. Humans are infected by two typ ...
. In animals, tsetse-vectored trypanosomiases include ''nagana'', ''souma'' (a French term which may not be a distinct condition
), and ''
surra
Surra (from the Marathi ''sūra'', meaning the sound of heavy breathing through nostrils, of imitative origin) is a disease of vertebrate animals. The disease is caused by protozoan trypanosomes, specifically ''Trypanosoma evansi'', of severa ...
'' according to the animal infected and the trypanosome species involved. The usage is not strict and while ''nagana'' generally refers to the disease in cattle and horses it is commonly used for any of the animal trypanosomiases.
Trypanosomes are animal
parasite
Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has ...
s, specifically
protozoa
Protozoa (singular: protozoan or protozoon; alternative plural: protozoans) are a group of single-celled eukaryotes, either free-living or parasitic, that feed on organic matter such as other microorganisms or organic tissues and debris. Histo ...
ns of the genus ''Trypanosoma''. These organisms are about the size of red blood cells. Different species of trypanosomes infect different hosts. They range widely in their effects on the vertebrate hosts. Some species, such as ''T. theileri'', do not seem to cause any health problems except perhaps in animals that are already sick.
Some
strains are much more
virulent
Virulence is a pathogen's or microorganism's ability to cause damage to a host.
In most, especially in animal systems, virulence refers to the degree of damage caused by a microbe to its host. The pathogenicity of an organism—its ability to ca ...
. Infected flies have an altered salivary composition which lowers feeding efficiency and consequently increases the feeding time, promoting trypanosome transmission to the vertebrate host. These trypanosomes are highly evolved and have developed a life cycle that requires periods in both the vertebrate and tsetse hosts.
Tsetse transmit trypanosomes in two ways, mechanical and biological transmission.
*Mechanical transmission involves the direct transmission of the same individual trypanosomes taken from an infected host into an uninfected host. The name 'mechanical' reflects the similarity of this mode of transmission to mechanical injection with a
syringe
A syringe is a simple reciprocating pump consisting of a plunger (though in modern syringes, it is actually a piston) that fits tightly within a cylindrical tube called a barrel. The plunger can be linearly pulled and pushed along the inside ...
. Mechanical transmission requires the tsetse to feed on an infected host and acquire trypanosomes in the blood meal, and then, within a relatively short period, to feed on an uninfected host and regurgitate some of the infected blood from the first blood meal into the tissue of the uninfected animal. This type of transmission occurs most frequently when tsetse are interrupted during a blood meal and attempt to satiate themselves with another meal. Other flies, such as
horse-flies, can also cause mechanical transmission of trypanosomes.
*Biological transmission requires a period of incubation of the trypanosomes within the tsetse host. The term 'biological' is used because trypanosomes must reproduce through several generations inside the tsetse host during the period of incubation (development within the fly is known as the extrinsic incubation period), which requires extreme
adaptation
In biology, adaptation has three related meanings. Firstly, it is the dynamic evolutionary process of natural selection that fits organisms to their environment, enhancing their evolutionary fitness. Secondly, it is a state reached by the po ...
of the trypanosomes to their tsetse host. In this mode of transmission, trypanosomes reproduce through several generations, changing in morphology at certain periods. This mode of transmission also includes the sexual phase of the trypanosomes. Tsetse are believed to be more likely to become infected by trypanosomes during their first few blood meals. Tsetse infected by trypanosomes are thought to remain infected for the remainder of their lives. Because of the adaptations required for biological transmission, trypanosomes that can be transmitted biologically by tsetse cannot be transmitted in this manner by other insects.
The relative importance of these two modes of transmission for the propagation of tsetse-vectored trypanosomiases is not yet well understood. However, since the sexual phase of the trypanosome life cycle occurs within the tsetse host, biological transmission is a required step in the life cycle of the tsetse-vectored trypanosomes.
The cycle of biological transmission of trypanosomiasis involves two phases, one inside the tsetse host and the other inside the vertebrate host. Trypanosomes are not passed between a pregnant tsetse and her offspring, so all newly emerged tsetse adults are free of infection. An uninfected fly that feeds on an infected vertebrate animal may acquire trypanosomes in its proboscis or gut. These trypanosomes, depending on the species, may remain in place, move to a different part of the digestive tract, or migrate through the tsetse body into the salivary glands. When an infected tsetse bites a susceptible host, the fly may regurgitate part of a previous blood meal that contains trypanosomes, or may inject trypanosomes in its saliva. Inoculation must contain a minimum of 300 to 450 individual trypanosomes to be successful, and may contain up to 40,000 cells.
In the case of ''T. b. brucei'' infecting ''G. p. gambiensis'', during this time the parasite changes the
proteome
The proteome is the entire set of proteins that is, or can be, expressed by a genome, cell, tissue, or organism at a certain time. It is the set of expressed proteins in a given type of cell or organism, at a given time, under defined conditions. ...
contents of the fly's head. This may be the reason/a reason for the behavioral changes seen, especially the unnecessarily increased feeding frequency, which increases transmission opportunities. This may be due in part to the altered
glucose
Glucose is a simple sugar with the molecular formula . Glucose is overall the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, using ...
metabolism observed, causing a perceived need for more calories. (The metabolic change, in turn, being due to complete absence of
glucose-6-phosphate 1-dehydrogenase in infected flies.)
Monoamine neurotransmitter
Monoamine neurotransmitters are neurotransmitters and neuromodulators that contain one amino group connected to an aromaticity, aromatic ring by a two-carbon chain (such as -CH2-CH2-). Examples are dopamine, norepinephrine and serotonin.
All mo ...
synthesis is also altered: Production of
aromatic L-amino acid decarboxylase
Aromatic L-amino acid decarboxylase (AADC or AAAD), also known as DOPA decarboxylase (DDC), tryptophan decarboxylase, and 5-hydroxytryptophan decarboxylase, is a lyase enzyme (), located in region 7p12.2-p12.1.
Mechanism
The enzyme uses pyri ...
- involved in
dopamine
Dopamine (DA, a contraction of 3,4-dihydroxyphenethylamine) is a neuromodulatory molecule that plays several important roles in cells. It is an organic compound, organic chemical of the catecholamine and phenethylamine families. Dopamine const ...
and
serotonin
Serotonin () or 5-hydroxytryptamine (5-HT) is a monoamine neurotransmitter. Its biological function is complex and multifaceted, modulating mood, cognition, reward, learning, memory, and numerous physiological processes such as vomiting and vas ...
synthesis - and
α-methyldopa hypersensitive protein was induced. This is very similar to the alterations in ''other''
dipteran
Flies are insects of the order Diptera, the name being derived from the Greek δι- ''di-'' "two", and πτερόν ''pteron'' "wing". Insects of this order use only a single pair of wings to fly, the hindwings having evolved into advanced ...
vectors' head proteomes under infection by ''other'' eukaryotic parasites of mammals, found in another study by the same team in the same year.
The trypanosomes are injected into vertebrate muscle tissue, but make their way, first into the
lymphatic system
The lymphatic system, or lymphoid system, is an organ system in vertebrates that is part of the immune system, and complementary to the circulatory system. It consists of a large network of lymphatic vessels, lymph nodes, lymphatic or lymphoid o ...
, then into the bloodstream, and eventually into the brain. The disease causes the swelling of the lymph glands, emaciation of the body, and eventually leads to death. Uninfected tsetse may bite the infected animal prior to its death and acquire the disease, thereby closing the transmission cycle.
Disease hosts and vectors
The tsetse-vectored trypanosomiases affect various vertebrate species including humans, antelopes, bovine cattle, camels, horses, sheep, goats, and pigs. These diseases are caused by several different trypanosome species that may also survive in wild animals such as crocodiles and monitor lizards. The diseases have different distributions across the African continent, so are transmitted by different species. This table summarizes this information:
In humans
Human African trypanosomiasis, also called
sleeping sickness
African trypanosomiasis, also known as African sleeping sickness or simply sleeping sickness, is an insect-borne parasitic infection of humans and other animals. It is caused by the species ''Trypanosoma brucei''. Humans are infected by two typ ...
, is caused by trypanosomes of the species ''Trypanosoma brucei''. This disease is invariably fatal if left untreated, but can almost always be cured with current medicines if the disease is diagnosed early enough.
Sleeping sickness begins with a tsetse bite leading to an inoculation in the subcutaneous tissue. The infection moves into the
lymphatic system
The lymphatic system, or lymphoid system, is an organ system in vertebrates that is part of the immune system, and complementary to the circulatory system. It consists of a large network of lymphatic vessels, lymph nodes, lymphatic or lymphoid o ...
, leading to a characteristic swelling of the lymph glands called ''Winterbottom's sign''. The infection progresses into the blood stream and eventually crosses into the
central nervous system
The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain and spinal cord. The CNS is so named because the brain integrates the received information and coordinates and influences the activity of all par ...
and invades the
brain
A brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as vision. It is the most complex organ in a v ...
leading to extreme
lethargy
Lethargy is a state of tiredness, sleepiness, weariness, fatigue, sluggishness or lack of energy. It can be accompanied by depression, decreased motivation, or apathy. Lethargy can be a normal response to inadequate sleep, overexertion, overwo ...
and eventually to
death
Death is the irreversible cessation of all biological functions that sustain an organism. For organisms with a brain, death can also be defined as the irreversible cessation of functioning of the whole brain, including brainstem, and brain ...
.
The species ''Trypanosoma brucei'', which causes the disease, has often been subdivided into three subspecies that were identified based either on the vertebrate hosts which the strain could infect or on the virulence of the disease in humans. The trypanosomes infectious to animals and not to humans were named ''Trypanosoma brucei brucei''. Strains that infected humans were divided into two subspecies based on their different virulences: ''Trypanosoma brucei gambiense'' was thought to have a slower onset and ''Trypanosoma brucei rhodesiense'' refers to strains with a more rapid, virulent onset. This characterization has always been problematic but was the best that could be done given the knowledge of the time and the tools available for identification. A recent molecular study using
restriction fragment length polymorphism analysis suggests that the three subspecies are
polyphyletic
A polyphyletic group is an assemblage of organisms or other evolving elements that is of mixed evolutionary origin. The term is often applied to groups that share similar features known as homoplasies, which are explained as a result of converg ...
, so the elucidation of the strains of ''T. brucei'' infective to humans requires a more complex explanation.
Procyclin
Procyclins also known as procyclic acidic repetitive proteins or PARP are proteins developed in the surface coating of ''Trypanosoma brucei'' parasites while in their tsetse fly vector. The cell surface of the bloodstream form features a ...
s are
protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...
s developed in the surface coating of trypanosomes whilst in their tsetse fly vector.
Other forms of human trypanosomiasis also exist but are not transmitted by tsetse. The most notable is American trypanosomiasis, known as
Chagas disease
Chagas disease, also known as American trypanosomiasis, is a tropical parasitic disease caused by ''Trypanosoma cruzi''. It is spread mostly by insects in the subfamily ''Triatominae'', known as "kissing bugs". The symptoms change over the cou ...
, which occurs in
South America
South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the southe ...
, caused by ''Trypanosoma cruzi'', and transmitted by certain insects of the
Reduviidae
The Reduviidae are a large cosmopolitan family of the order Hemiptera (true bugs). Among the Hemiptera and together with the Nabidae almost all species are terrestrial ambush predators: most other predatory Hemiptera are aquatic. The main exampl ...
, members of the
Hemiptera
Hemiptera (; ) is an order (biology), order of insects, commonly called true bugs, comprising over 80,000 species within groups such as the cicadas, aphids, planthoppers, leafhoppers, Reduviidae, assassin bugs, Cimex, bed bugs, and shield bugs. ...
.
In domestic animals
Animal
trypanosomiasis
Trypanosomiasis or trypanosomosis is the name of several diseases in vertebrates caused by parasitic protozoan trypanosomes of the genus ''Trypanosoma''. In humans this includes African trypanosomiasis and Chagas disease. A number of other diseas ...
, also called ''nagana'' when it occurs in
bovine cattle or
horse
The horse (''Equus ferus caballus'') is a domesticated, one-toed, hoofed mammal. It belongs to the taxonomic family Equidae and is one of two extant subspecies of ''Equus ferus''. The horse has evolved over the past 45 to 55 million y ...
s or ''sura'' when it occurs in domestic
pig
The pig (''Sus domesticus''), often called swine, hog, or domestic pig when distinguishing from other members of the genus '' Sus'', is an omnivorous, domesticated, even-toed, hoofed mammal. It is variously considered a subspecies of ''Sus s ...
s, is caused by several trypanosome species. These
disease
A disease is a particular abnormal condition that negatively affects the structure or function of all or part of an organism, and that is not immediately due to any external injury. Diseases are often known to be medical conditions that a ...
s reduce the growth rate,
milk
Milk is a white liquid food produced by the mammary glands of mammals. It is the primary source of nutrition for young mammals (including breastfed human infants) before they are able to digestion, digest solid food. Immune factors and immune ...
productivity, and strength of
farm
A farm (also called an agricultural holding) is an area of land that is devoted primarily to agricultural processes with the primary objective of producing food and other crops; it is the basic facility in food production. The name is used fo ...
animals, generally leading to the eventual
death
Death is the irreversible cessation of all biological functions that sustain an organism. For organisms with a brain, death can also be defined as the irreversible cessation of functioning of the whole brain, including brainstem, and brain ...
of the infected animals. Certain species of cattle are called ''
trypanotolerant
A trypanotolerant organism is one which is relatively less affected by trypanosome infestation.
By host In humans
In livestock
Some breeds are known for their trypanotolerance. This is especially important in Africa where a few particular try ...
'' because they can survive and grow even when infected with trypanosomes although they also have lower productivity rates when infected.
The course of the disease in animals is similar to the course of
sleeping sickness
African trypanosomiasis, also known as African sleeping sickness or simply sleeping sickness, is an insect-borne parasitic infection of humans and other animals. It is caused by the species ''Trypanosoma brucei''. Humans are infected by two typ ...
in humans.
''Trypanosoma congolense'' and ''Trypanosoma vivax'' are the two most important species infecting bovine cattle in
sub-Saharan Africa
Sub-Saharan Africa is, geographically, the area and regions of the continent of Africa that lies south of the Sahara. These include West Africa, East Africa, Central Africa, and Southern Africa. Geopolitically, in addition to the List of sov ...
. ''Trypanosoma simiae'' causes a virulent disease in
swine.
Other forms of animal trypanosomiasis are also known from other areas of the globe, caused by different species of trypanosomes and transmitted without the intervention of the tsetse fly.
The tsetse fly vector ranges mostly in the central part of Africa.
Trypanosomiasis
Trypanosomiasis or trypanosomosis is the name of several diseases in vertebrates caused by parasitic protozoan trypanosomes of the genus ''Trypanosoma''. In humans this includes African trypanosomiasis and Chagas disease. A number of other diseas ...
poses a considerable constraint on livestock agricultural development in Tsetse fly infested areas of sub Saharan Africa, especially in west and central Africa. International research conducted by
ILRI
The International Livestock Research Institute or ILRI is an international agricultural research institute within the CGIAR – formerly the Consultative Group for International Agricultural Research. It was established in 1994 by merger of th ...
in
Nigeria
Nigeria ( ), , ig, Naìjíríyà, yo, Nàìjíríà, pcm, Naijá , ff, Naajeeriya, kcg, Naijeriya officially the Federal Republic of Nigeria, is a country in West Africa. It is situated between the Sahel to the north and the Gulf o ...
, the
Democratic Republic of the Congo
The Democratic Republic of the Congo (french: République démocratique du Congo (RDC), colloquially "La RDC" ), informally Congo-Kinshasa, DR Congo, the DRC, the DROC, or the Congo, and formerly and also colloquially Zaire, is a country in ...
and
Kenya
)
, national_anthem = "Ee Mungu Nguvu Yetu"()
, image_map =
, map_caption =
, image_map2 =
, capital = Nairobi
, coordinates =
, largest_city = Nairobi
, ...
has shown that the
N'Dama
N'Dama is a breed of cattle from West Africa. Other names for them include Boenca or Boyenca (Guinea-Bissau), Fouta Jallon, ''Djallonké'' or ''Djallonké cattle'', Fouta Longhorn, Fouta Malinke, Futa, Malinke, Mandingo (Liberia), and N'Dama Peti ...
is the most resistant breed.
Control
The conquest of
sleeping sickness
African trypanosomiasis, also known as African sleeping sickness or simply sleeping sickness, is an insect-borne parasitic infection of humans and other animals. It is caused by the species ''Trypanosoma brucei''. Humans are infected by two typ ...
and
nagana
Animal trypanosomiasis, also known as nagana and nagana pest, or sleeping sickness, is a disease of vertebrates. The disease is caused by trypanosomes of several species in the genus ''Trypanosoma'' such as ''Trypanosoma brucei''. ''Trypanosoma ...
would be of immense benefit to rural development and contribute to poverty alleviation and improved food security in sub-Saharan Africa. Human African trypanosomosis (HAT) and animal African trypanosomosis (AAT) are sufficiently important to make virtually any intervention against these diseases beneficial.
![Tsetse-BKF-3](https://upload.wikimedia.org/wikipedia/commons/6/68/Tsetse-BKF-3.jpg)
The disease can be managed by controlling the vector and thus reducing the incidence of the disease by disrupting the transmission cycle. Another tactic to manage the disease is to target the disease directly using surveillance and
curative or
prophylactic
Preventive healthcare, or prophylaxis, consists of measures taken for the purposes of disease prevention.Hugh R. Leavell and E. Gurney Clark as "the science and art of preventing disease, prolonging life, and promoting physical and mental hea ...
treatments to reduce the number of hosts that carry the disease.
Economic analysis indicates that the cost of managing
trypanosomosis
Trypanosomiasis or trypanosomosis is the name of several diseases in vertebrates caused by parasitic protozoan trypanosomes of the genus ''Trypanosoma''. In humans this includes African trypanosomiasis and Chagas disease. A number of other diseas ...
through the elimination of important populations of major tsetse vectors will be covered several times by the benefits of tsetse-free status.
Area-wide interventions against the tsetse and trypanosomosis problem appear more efficient and profitable if sufficiently large areas, with high numbers of cattle, can be covered.
Vector control strategies can aim at either continuous
suppression or eradication of target populations. Tsetse fly eradication programmes are complex and logistically demanding activities and usually involve the integration of different control tactics, such as
trypanocidal A trypanocidal agent is an antiprotozoal agent that acts upon trypanosome parasites.
Examples include:
* Aminoquinuride
* benzonidazole
* blasticidin S
* DAPI
* diminazene
* diminazene aceturate
* eflornithine
* ethidium
* isometamidium chlori ...
drugs,
impregnated treated targets (ITT),
insecticide-treated cattle (ITC),
aerial spraying
Aerial application, or what is informally referred to as crop dusting, involves spraying crops with crop protection products from an agricultural aircraft. Planting certain types of seed are also included in aerial application. The specific sp ...
(
Sequential Aerosol Technique - SAT) and in some situations the release of sterile males (
sterile insect technique
The sterile insect technique (SIT) is a method of biological insect control, whereby overwhelming numbers of sterile insects are released into the wild. The released insects are preferably male, as this is more cost-effective and the females ma ...
– SIT). To ensure sustainability of the results, it is critical to apply the control tactics on an area-wide basis, i.e. targeting an entire tsetse population that is preferably
genetically isolated.
Control techniques
Many techniques have reduced tsetse populations, with earlier, crude methods recently replaced by methods that are cheaper, more directed, and ecologically better.
Slaughter of wild animals
One early technique involved slaughtering all the wild animals tsetse fed on. For example, the island of
Principe off the west coast of Africa was entirely cleared of
feral
A feral () animal or plant is one that lives in the wild but is descended from domesticated individuals. As with an introduced species, the introduction of feral animals or plants to non-native regions may disrupt ecosystems and has, in some ...
pigs in the 1930s, which led to the
extirpation
Local extinction, also known as extirpation, refers to a species (or other taxon) of plant or animal that ceases to exist in a chosen geographic area of study, though it still exists elsewhere. Local extinctions are contrasted with global extinct ...
of the fly. While the fly eventually re-invaded in the 1950s, the new population of tsetse was free from the disease.
Land clearing
Another early technique involved
complete removal of brush and woody vegetation from an area.
However, the technique was not widely used and has been abandoned. Tsetse tend to rest on the trunks of trees so removing woody vegetation made the area inhospitable to the flies. Until about 1959 this was done by hand and so was quite time consuming. Glover et al 1959 describes the technique which they call "
chain clearing
Deforestation or forest clearance is the removal of a forest or stand of trees from land that is then converted to non-forest use. Deforestation can involve conversion of forest land to farms, ranches, or urban use. The most concentrated d ...
". Chain clearing drags a chain forward between two heavy vehicles and thereby does the same job much more quickly - but still at some expense.
Preventing regrowth of woody vegetation requires continuous clearing efforts which is even more expensive,
and only practical where large human populations are present. Also, the clearing of woody vegetation has come to be seen as an environmental problem more than a benefit.
Pesticide campaigns
Pesticides
Pesticides are substances that are meant to control pests. This includes herbicide, insecticide, nematicide, molluscicide, piscicide, avicide, rodenticide, bactericide, insect repellent, animal repellent, microbicide, fungicide, and lampric ...
have been used to control tsetse starting initially during the early part of the twentieth century in localized efforts using the inorganic metal-based pesticides, expanding after the Second World War into massive aerial- and ground-based campaigns with organochlorine pesticides such as
DDT
Dichlorodiphenyltrichloroethane, commonly known as DDT, is a colorless, tasteless, and almost odorless crystalline chemical compound, an organochloride. Originally developed as an insecticide, it became infamous for its environmental impacts. ...
applied as
aerosol
An aerosol is a suspension (chemistry), suspension of fine solid particles or liquid Drop (liquid), droplets in air or another gas. Aerosols can be natural or Human impact on the environment, anthropogenic. Examples of natural aerosols are fog o ...
sprays at
Ultra-Low Volume Ultra-low volume (ULV) application of pesticides has been defined as spraying at Volume Application Rate(VAR) of less than 5 L/ha for field crops or less than 50 L/ha for tree/bush crops. VARs of 0.25 – 2 L/ha are typical for aerial ULV appl ...
rates. Later, more targeted techniques used ''pour-on''
formulations
Formulation is a term used in various senses in various applications, both the material and the abstract or formal. Its fundamental meaning is the putting together of components in appropriate relationships or structures, according to a formul ...
in which advanced organic pesticides were applied directly to the backs of cattle.
Trapping
Tsetse populations can be monitored and effectively controlled using simple, inexpensive
traps. These often use electric blue cloth, either in sheet or biconical form, since this color attracts the flies. The traps work by channeling the flies into a collection chamber, or by exposing the flies to
insecticide
Insecticides are substances used to kill insects. They include ovicides and larvicides used against insect eggs and larvae, respectively. Insecticides are used in agriculture, medicine, industry and by consumers. Insecticides are claimed to b ...
sprayed on the cloth. Early traps mimicked the form of cattle, as tsetse are also attracted to large dark colors like the hides of
cow
Cattle (''Bos taurus'') are large, domesticated, cloven-hooved, herbivores. They are a prominent modern member of the subfamily Bovinae and the most widespread species of the genus ''Bos''. Adult females are referred to as cows and adult ma ...
s and
buffaloes. Some scientists put forward the idea that
zebra
Zebras (, ) (subgenus ''Hippotigris'') are African equines with distinctive black-and-white striped coats. There are three living species: the Grévy's zebra (''Equus grevyi''), plains zebra (''E. quagga''), and the mountain zebra (''E. zeb ...
have stripes, not as a camouflage in long grass, but because the black and white bands tend to confuse tsetse and prevent attack.
The use of chemicals as attractants to lure tsetse to the traps has been studied extensively in the late 20th century, but this has mostly been of interest to scientists rather than as an economically reasonable solution. Attractants studied have been those tsetse might use to find food, like
carbon dioxide
Carbon dioxide (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...
,
octenol, and
acetone
Acetone (2-propanone or dimethyl ketone), is an organic compound with the formula . It is the simplest and smallest ketone (). It is a colorless, highly volatile and flammable liquid with a characteristic pungent odour.
Acetone is miscib ...
—which are given off in animals' breath and distributed downwind in an ''odor plume.'' Synthetic versions of these chemicals can create artificial odor plumes. A cheaper approach is to place cattle
urine
Urine is a liquid by-product of metabolism in humans and in many other animals. Urine flows from the kidneys through the ureters to the urinary bladder. Urination results in urine being excretion, excreted from the body through the urethra.
Cel ...
in a half gourd near the trap. For large trapping efforts, additional traps are generally cheaper than expensive artificial attractants.
A special trapping method is applied in
Ethiopia
Ethiopia, , om, Itiyoophiyaa, so, Itoobiya, ti, ኢትዮጵያ, Ítiyop'iya, aa, Itiyoppiya officially the Federal Democratic Republic of Ethiopia, is a landlocked country in the Horn of Africa. It shares borders with Eritrea to the ...
, where the BioFarm Consortium (
ICIPE
The International Centre of Insect Physiology and Ecology (ICIPE, branded as ''icipe'') is an international scientific research institute, headquartered in Nairobi, Kenya that works towards improving lives and livelihoods of people in Africa.
I ...
, BioVision Foundation, BEA, Helvetas,
DLCO-EA
The Desert Locust Control Organization for Eastern Africa (DLCO-EA) is "a regional pest and vector management organization established by an International Convention signed in Addis Ababa, Ethiopia in 1962".Praxis Ethiopia
Praxis Ethiopia is an international organisation whose goal is to apply professional expertise to the problems of extreme poverty in Ethiopia. The word "Praxis" comes from the Greek language, and meaning the application of knowledge to solve proble ...
) applies the traps in a
sustainable agriculture
Sustainable agriculture is farming in sustainable ways meeting society's present food and textile needs, without compromising the ability for current or future generations to meet their needs. It can be based on an understanding of ecosystem ser ...
and
rural development
Rural development is the process of improving the quality life and economic well-being of people living in rural areas, often relatively isolated and sparsely populated areas.
Rural development has traditionally centered on the exploitation of l ...
context (SARD). The traps are just the entry point, followed by improved farming, human health and marketing inputs. This method is in the final stage of testing (as of 2006).
Sterile insect technique
The
sterile insect technique
The sterile insect technique (SIT) is a method of biological insect control, whereby overwhelming numbers of sterile insects are released into the wild. The released insects are preferably male, as this is more cost-effective and the females ma ...
(SIT) is a form of pest control that uses
ionizing radiation
Ionizing radiation (or ionising radiation), including nuclear radiation, consists of subatomic particles or electromagnetic waves that have sufficient energy to ionize atoms or molecules by detaching electrons from them. Some particles can travel ...
(
gamma ray
A gamma ray, also known as gamma radiation (symbol γ or \gamma), is a penetrating form of electromagnetic radiation arising from the radioactive decay of atomic nuclei. It consists of the shortest wavelength electromagnetic waves, typically ...
or
X-ray
An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10 nanometers, corresponding to frequencies in the range 30&nb ...
) to sterilize male flies that are mass-produced in special rearing facilities. The sterile males are released systematically from the ground or by air in tsetse-infested areas, where they mate with wild females, which do not produce offspring. As a result, this technique can eventually eradicate populations of wild flies. SIT is among the most
environmentally friendly
Environment friendly processes, or environmental-friendly processes (also referred to as eco-friendly, nature-friendly, and green), are sustainability and marketing terms referring to goods and services, laws, guidelines and policies that clai ...
control tactics available, and is usually applied as the final component of an integrated campaign. It has been used to subdue the populations of many other fly species including the medfly, ''
Ceratitis capitata
''Ceratitis capitata'', commonly known as the Mediterranean fruit fly or medfly, is a yellow-and-brown fly native to sub-Saharan Africa. It has no near relatives in the Western Hemisphere and is considered to be one of the most destructive frui ...
''.
The sustainable removal of the tsetse fly is in many cases the most cost-effective way of dealing with the T&T problem resulting in major economic benefits for subsistence farmers in rural areas. Insecticide-based methods are normally very ineffective in removing the last remnants of tsetse populations, while, on the contrary, sterile males are very effective in finding and mating the last remaining females. Therefore, the integration of the SIT as the last component of an area-wide integrated approach is essential in many situations to achieve complete eradication of the different tsetse populations, particularly in areas of more dense vegetation.
A project that was implemented from 1994 to 1997 on the Island of
Unguja
Unguja (also referred to as "Zanzibar Island" or simply "Zanzibar", in grc, Μενουθιάς, Menuthias – as mentioned in The ''Periplus of the Erythraean Sea'') is the largest and most populated island of the Zanzibar archipelago, in Tanza ...
,
Zanzibar
Zanzibar (; ; ) is an insular semi-autonomous province which united with Tanganyika in 1964 to form the United Republic of Tanzania. It is an archipelago in the Indian Ocean, off the coast of the mainland, and consists of many small islands ...
(United Republic of
Tanzania
Tanzania (; ), officially the United Republic of Tanzania ( sw, Jamhuri ya Muungano wa Tanzania), is a country in East Africa within the African Great Lakes region. It borders Uganda to the north; Kenya to the northeast; Comoro Islands and ...
), demonstrated that, after suppression of the tsetse population with insecticides, SIT completely removed the ''
Glossina austeni
Tsetse ( , or ) (sometimes spelled tzetze; also known as tik-tik flies), are large, biting flies that inhabit much of tropical Africa. Tsetse flies include all the species in the genus ''Glossina'', which are placed in their own family, Glo ...
'' Newstead population from the Island.
This was carried out without any understanding of the
population genetics
Population genetics is a subfield of genetics that deals with genetic differences within and between populations, and is a part of evolutionary biology. Studies in this branch of biology examine such phenomena as adaptation, speciation, and pop ...
of ''G. a.'', but future SIT efforts can benefit from such preparation. Population genetics would help to select the ''Glossina'' population to be deployed for similarity to the target population.
[ ] The eradication of the tsetse fly from Unguja Island in 1997 was followed by the disappearance of the AAT which enabled farmers to integrate livestock keeping with cropping in areas where this had been impossible before. The increased livestock and crop productivity and the possibility of using animals for transport and traction significantly contributed to an increase in the quality of people's lives. Surveys in 1999, 2002, 2014, and 2015 have confirmed this success - continued absence of tsetse and
nagana
Animal trypanosomiasis, also known as nagana and nagana pest, or sleeping sickness, is a disease of vertebrates. The disease is caused by trypanosomes of several species in the genus ''Trypanosoma'' such as ''Trypanosoma brucei''. ''Trypanosoma ...
on the island.
In the
Niayes Niayes is a geographical area in northwestern Senegal which forms a coastal strip, with sand dunes adjoining the sea being backed by a string of fresh water lakes. The land is used for horticulture and the grazing of cattle, and provides suitable h ...
region of
Senegal
Senegal,; Wolof: ''Senegaal''; Pulaar: 𞤅𞤫𞤲𞤫𞤺𞤢𞥄𞤤𞤭 (Senegaali); Arabic: السنغال ''As-Sinighal'') officially the Republic of Senegal,; Wolof: ''Réewum Senegaal''; Pulaar : 𞤈𞤫𞤲𞤣𞤢𞥄𞤲𞤣𞤭 ...
, a coastal area close to
Dakar
Dakar ( ; ; wo, Ndakaaru) (from daqaar ''tamarind''), is the capital and largest city of Senegal. The city of Dakar proper has a population of 1,030,594, whereas the population of the Dakar metropolitan area is estimated at 3.94 million in 2 ...
, livestock keeping was difficult due to the presence of a population of ''
Glossina palpalis gambiensis
Tsetse ( , or ) (sometimes spelled tzetze; also known as tik-tik flies), are large, biting flies that inhabit much of tropical Africa. Tsetse flies include all the species in the genus ''Glossina'', which are placed in their own family, Glo ...
''. Feasibility studies indicated that the fly population was confined to very fragmented habitats and a population genetics study indicated that the population was genetically isolated from the main tsetse belt in the south eastern part of Senegal. After completion of the feasibility studies (2006–2010), an area-wide integrated eradication campaign that included an SIT component was started in 2011, and by 2015, the Niayes region had become almost tsetse fly free. This has allowed a change of
cattle breed
List of cattle breeds — Over 1000 breeds of cattle are recognized worldwide, some of which adapted to the local climate, others which were bred by humans for specialized uses.
Cattle breeds fall into two main types, which are regarded as eithe ...
s from lower producing
trypanotolerant
A trypanotolerant organism is one which is relatively less affected by trypanosome infestation.
By host In humans
In livestock
Some breeds are known for their trypanotolerance. This is especially important in Africa where a few particular try ...
breeds to higher-producing foreign breeds.
The entire target area (Block 1, 2 and 3) has a total surface of 1000 km2, and the first block (northern part) can be considered free of tsetse, as intensive monitoring has failed to detect since 2012 a single wild tsetse fly. The prevalence of AAT has decreased from 40 to 50% before the project started to less than 10% to date in blocks 1 and 2. Although insecticides are being used for fly suppression, they are applied for short periods on traps, nets and livestock, and are not spread into the environment. After the suppression activities are completed, no more insecticide is applied in the area. The removal of trypanosomosis will eliminate the need for constant prophylactic treatments of the cattle with trypanocidal drugs, therefore reducing
residue
Residue may refer to:
Chemistry and biology
* An amino acid, within a peptide chain
* Crop residue, materials left after agricultural processes
* Pesticide residue, refers to the pesticides that may remain on or in food after they are applied ...
s of these drugs in the
dung, meat and milk.
The main beneficiaries of the project are the many small holder farmers, the larger commercial farms and the consumers of meat and milk. According to a socio-economic survey and benefit cost analysis, after eradication of the tsetse farmers will be able to replace their local breeds with improved breeds and increase their annual income by €2.8 million. In addition, it is expected that the number of cattle will be reduced by 45%, which will result in reduced environmental impacts.
Societal impact
In the literature of
environmental determinism
Environmental determinism (also known as climatic determinism or geographical determinism) is the study of how the physical environment predisposes societies and states towards particular development trajectories. Jared Diamond, Jeffrey Herbst, ...
, the tsetse has been linked to difficulties during early
state formation
State formation is the process of the development of a centralized government structure in a situation where one did not exist prior to its development. State formation has been a study of many disciplines of the social sciences for a number of ...
for areas where the fly is prevalent. A 2012 study used population growth models, physiological data, and ethnographic data to examine pre-colonial agricultural practices and isolate the effects of the fly. A "tsetse suitability index" was developed from insect population growth, climate and geospatial data to simulate the fly's population steady state. An increase in the tsetse suitability index was associated with a statistically significant weakening of the agriculture, levels of urbanization, institutions and subsistence strategies. Results suggest that the tsetse decimated livestock populations, forcing early states to rely on slave labor to clear land for farming, and preventing farmers from taking advantage of natural animal fertilizers to increase crop production. These long-term effects may have kept population density low and discouraged cooperation between small-scale communities, thus preventing stronger nations from forming.
The authors also suggest that under a lower burden of tsetse, Africa would have developed differently. Agriculture (measured by the usage of large domesticated animals, intensive agriculture, plow use and female participation rate in agriculture) as well as institutions (measured by the appearance of indigenous slavery and levels of centralization) would have been more like those found in Eurasia. Qualitative support for this claim comes from archaeological findings; e.g.,
Great Zimbabwe
Great Zimbabwe is a medieval city in the south-eastern hills of Zimbabwe near Lake Mutirikwi and the town of Masvingo. It is thought to have been the capital of a great kingdom during the country's Late Iron Age about which little is known. Con ...
is located in the African highlands where the fly does not occur, and represented the largest and technically most advanced precolonial structure in Southern sub-Sahara Africa.
Other authors are more skeptical that the Tsetse fly had such an immense influence on African development. One conventional argument is that the Tsetse fly made it difficult to use draught animals. Hence, wheeled forms of transportations were not used as well. While this is certainly true for areas with high densities of the fly, similar cases outside tsetse-suitable areas exist. While the fly definitely had a relevant influence on the adoption of new technologies in Africa, it has been contended that it does not represent the single root cause.
History
According to an article in the
New Scientist
''New Scientist'' is a magazine covering all aspects of science and technology. Based in London, it publishes weekly English-language editions in the United Kingdom, the United States and Australia. An editorially separate organisation publishe ...
, the depopulated and apparently primevally wild Africa seen in wildlife documentary films was formed in the 19th century by disease, a combination of
rinderpest
Rinderpest (also cattle plague or steppe murrain) was an infectious viral disease of cattle, domestic buffalo, and many other species of even-toed ungulates, including gaurs, buffaloes, large antelope, deer, giraffes, wildebeests, and warthogs ...
and the tsetse fly. Rinderpest is believed to have originated in Asia, later spreading through the transport of cattle.
In 1887, the rinderpest virus was accidentally imported in livestock brought by an Italian expeditionary force to Eritrea. It spread rapidly, reaching Ethiopia by 1888, the Atlantic coast by 1892 and South Africa by 1897. Rinderpest, a cattle plague from central Asia, killed over 90% of the cattle of the pastoral peoples such as the
Masai of east Africa. In South Africa, with no native
immunity
Immunity may refer to:
Medicine
* Immunity (medical), resistance of an organism to infection or disease
* ''Immunity'' (journal), a scientific journal published by Cell Press
Biology
* Immune system
Engineering
* Radiofrequence immunity desc ...
, most of the population – some 5.5 million domestic cattle – died. Pastoralists and farmers were left with no animals – their source of income – and farmers were deprived of their working animals for ploughing and irrigation. The pandemic coincided with a period of drought, causing widespread famine. The starving human populations died of smallpox, cholera, and typhoid, as well as African Sleeping Sickness and other endemic diseases. It is estimated that two-thirds of the Masai died in 1891.
The land was left emptied of its cattle and its people, enabling the colonial powers Germany and Britain to take over Tanzania and Kenya with little effort. With greatly reduced grazing, grassland turned rapidly to bush. The closely cropped grass sward was replaced in a few years by woody grassland and thornbush, ideal habitat for tsetse flies. Wild mammal populations increased rapidly, accompanied by the tsetse fly.
Highland
Highlands or uplands are areas of high elevation such as a mountainous region, elevated mountainous plateau or high hills. Generally speaking, upland (or uplands) refers to ranges of hills, typically from up to while highland (or highlands) is ...
regions of east Africa which had been free of tsetse fly were colonised by the pest, accompanied by sleeping sickness, until then unknown in the area. Millions of people died of the disease in the early 20th century.
[
]
The areas occupied by the tsetse fly were largely barred to animal husbandry
Animal husbandry is the branch of agriculture concerned with animals that are raised for meat, fibre, milk, or other products. It includes day-to-day care, selective breeding, and the raising of livestock. Husbandry has a long history, starti ...
. Sleeping sickness was dubbed "the best game warden in Africa" by conservationists, who assumed that the land, empty of people and full of game animals, had always been like that. Julian Huxley
Sir Julian Sorell Huxley (22 June 1887 – 14 February 1975) was an English evolutionary biologist, eugenicist, and internationalist. He was a proponent of natural selection, and a leading figure in the mid-twentieth century modern synthesis. ...
of the World Wildlife Fund
The World Wide Fund for Nature Inc. (WWF) is an international non-governmental organization founded in 1961 that works in the field of wilderness preservation and the reduction of human impact on the environment. It was formerly named the Wo ...
called the plains of east Africa "a surviving sector of the rich natural world as it was before the rise of modern man".[ They created numerous large reserves for hunting ]safari
A safari (; ) is an overland journey to observe wild animals, especially in eastern or southern Africa. The so-called "Big Five" game animals of Africa – lion, leopard, rhinoceros, elephant, and Cape buffalo – particularly form an importa ...
s. In 1909 the newly retired president Theodore Roosevelt
Theodore Roosevelt Jr. ( ; October 27, 1858 – January 6, 1919), often referred to as Teddy or by his initials, T. R., was an American politician, statesman, soldier, conservationist, naturalist, historian, and writer who served as the 26t ...
went on a safari that brought over 10,000 animal carcasses to America. Later, much of the land was turned over to nature reserves and national parks
A national park is a natural park in use for conservation purposes, created and protected by national governments. Often it is a reserve of natural, semi-natural, or developed land that a sovereign state declares or owns. Although individual ...
such as the Serengeti
The Serengeti ( ) ecosystem is a geographical region in Africa, spanning northern Tanzania. The protected area within the region includes approximately of land, including the Serengeti National Park and several game reserves. The Serengeti ...
, Masai Mara
Maasai Mara, also sometimes spelled Masai Mara and locally known simply as The Mara, is a large national game reserve in Narok, Kenya, contiguous with the Serengeti National Park in Tanzania. It is named in honor of the Maasai people, the ancestr ...
, Kruger Krüger, Krueger or Kruger (without the Umlaut (diacritic), umlaut Ü) are German surnames originating from '':de:Krüger, Krüger'', meaning tavern-keeper in Low German and Pottery, potter in Central German and Upper German.
The last name Krüger ...
and Okavango Delta
The Okavango Delta (or Okavango Grassland; formerly spelled "Okovango" or "Okovanggo") in Botswana is a swampy inland delta formed where the Okavango River reaches a tectonic trough at an altitude of 930–1,000 m in the central part of the en ...
. The result, across eastern and southern Africa, is a modern landscape of manmade ecosystems: farmland and pastoral land largely free of bush and tsetse fly; and bush controlled by the tsetse fly. [
Although the colonial powers saw the disease as a threat to their interests, and acted accordingly to bring transmission almost to a halt in the 1960s,] this improved situation led to a laxity of surveillance and management by the newly independent governments covering the same areas - and a resurgence that became a crisis again in the 1990s.
Current situation
Tsetse flies are regarded as a major cause of rural poverty in sub-Saharan Africa
Sub-Saharan Africa is, geographically, the area and regions of the continent of Africa that lies south of the Sahara. These include West Africa, East Africa, Central Africa, and Southern Africa. Geopolitically, in addition to the List of sov ...
because they prevent mixed farming. The land infested with tsetse flies is often cultivated by people using hoes rather than more efficient draught animals because ''nagana
Animal trypanosomiasis, also known as nagana and nagana pest, or sleeping sickness, is a disease of vertebrates. The disease is caused by trypanosomes of several species in the genus ''Trypanosoma'' such as ''Trypanosoma brucei''. ''Trypanosoma ...
'', the disease transmitted by tsetse, weakens and often kills these animals. Cattle that do survive produce little milk, pregnant cows often abort their calves, and manure is not available to fertilize the worn-out soils.
The disease ''nagana'' or African animal trypanosomiasis
Animal trypanosomiasis, also known as nagana and nagana pest, or sleeping sickness, is a disease of vertebrates. The disease is caused by trypanosomes of several species in the genus ''Trypanosoma'' such as ''Trypanosoma brucei''. ''Trypanosoma ...
(AAT) causes gradual health decline in infected livestock, reduces milk and meat production, and increases abortion rates. Animals eventually succumb to the disease - annual cattle deaths caused by trypanosomiasis are estimated at 3 million, reducing annual cattle production value by US$600m-US$1.2b. This has an enormous impact on the livelihood of farmers who live in tsetse-infested areas, as infected animals cannot be used to plough the land, and keeping cattle is only feasible when the animals are kept under constant prophylactic
Preventive healthcare, or prophylaxis, consists of measures taken for the purposes of disease prevention.Hugh R. Leavell and E. Gurney Clark as "the science and art of preventing disease, prolonging life, and promoting physical and mental hea ...
treatment with trypanocidal drugs, often with associated problems of drug resistance
Drug resistance is the reduction in effectiveness of a medication such as an antimicrobial or an antineoplastic in treating a disease or condition. The term is used in the context of resistance that pathogens or cancers have "acquired", that is, ...
, counterfeited drugs, and suboptimal dosage. The overall annual direct lost potential in livestock and crop production was estimated at US$4.5 billion[Budd, L. 1999. DFID-funded tsetse and trypanosome research and development since 1980. Vol. 2. Economic analysis. Aylesford, UK, DFID Livestock Production, Animal Health and Natural Resources Systems Research Programmes]-US$4.75b.
The tsetse fly lives in nearly in sub-Saharan Africa (mostly wet tropical forest) and many parts of this large area is fertile land that is left uncultivated—a so-called green desert
''Green Desert'' is the twenty-seventh major release and the fifteenth studio album by Electronic music, electronic artists Tangerine Dream. The music was recorded in Berlin in 1973, during a period when Peter Baumann had temporarily left Germany ...
not used by humans and cattle. Most of the 38 countries infested with tsetse are poor, debt-ridden and underdeveloped. Of the 38 tsetse-infested countries, 32 ar
low-income, food-deficit countries
29 are least developed countries, and 30 or 34 are among the 40 most heavily indebted poor countries
The heavily indebted poor countries (HIPC) are a group of 39 developing countries with high levels of poverty and debt overhang which are eligible for special assistance from the International Monetary Fund (IMF) and the World Bank.
The HIPC ...
. Eradicating the tsetse and trypanosomiasis (T&T) problem would allow rural Africans to use these areas for animal husbandry
Animal husbandry is the branch of agriculture concerned with animals that are raised for meat, fibre, milk, or other products. It includes day-to-day care, selective breeding, and the raising of livestock. Husbandry has a long history, starti ...
or the cultivation of crops and hence increase food production. Only 45 million cattle, of 172 million present in sub-Saharan Africa, are kept in tsetse-infested areas but are often forced into fragile ecosystems like highlands or the semiarid
A semi-arid climate, semi-desert climate, or steppe climate is a dry climate sub-type. It is located on regions that receive precipitation below potential evapotranspiration, but not as low as a desert climate. There are different kinds of semi-ar ...
Sahel
The Sahel (; ar, ساحل ' , "coast, shore") is a region in North Africa. It is defined as the ecoclimatic and biogeographic realm of transition between the Sahara to the north and the Sudanian savanna to the south. Having a hot semi-arid c ...
zone, which increases overgrazing and overuse of land for food production.
In addition to this direct impact, the presence of tsetse and trypanosomiasis discourages the use of more productive exotic and cross-bred cattle, depresses the growth and affects the distribution of livestock populations, reduces the potential opportunities for livestock and crop production (mixed farming) through less draught power to cultivate land and less manure to fertilize (in an environment-friendly way) soils for better crop production, and affects human settlements (people tend to avoid areas with tsetse flies).
Tsetse flies transmit a similar disease to humans, called African trypanosomiasis
African trypanosomiasis, also known as African sleeping sickness or simply sleeping sickness, is an insect-borne parasitic infection of humans and other animals. It is caused by the species ''Trypanosoma brucei''. Humans are infected by two typ ...
, human African trypanosomiasis (HAT) or sleeping sickness. An estimated 60-70 million people in 20 countries are at different levels of risk and only 3-4 million people are covered by active surveillance. The DALY Daly or DALY may refer to:
Places Australia
* County of Daly, a cadastral division in South Australia
* Daly River, Northern Territory, a locality
* Electoral division of Daly, an electorate in the Northern Territory
* Daly, Northern Territory, ...
index (disability-adjusted life years), an indicator to quantify the burden of disease, includes the impact of both the duration of life lost due to premature death and the duration of life lived with a disability. The annual burden of sleeping sickness is estimated at 2 million DALYs. Since the disease tends to affect economically active adults, the total cost to a family with a patient is about 25% of a year's income.
History of study
In East Africa, C. F. M. Swynnerton played a large role in the first half of the 20th century. Swynnerton did much of the earliest tsetse ecology research.[''Clement Gillman, 1882-1946: Biographical Notes on a Pioneer East African Geographer''. ]East African Geographical Review
The ''African Geographical Review'' is a biannual Peer review, peer-reviewed academic journal published by Taylor & Francis on behalf of the American Association of Geographers' Africa Specialty Group.
The journal was originally established in 196 ...
. Makerere:Makerere University
Makerere University, Kampala (; Mak) is Uganda's largest and oldest institution of higher learning, first established as a technical school in 1922. It became an independent national university in 1970. Today, Makerere University is composed of ni ...
. Hoyle, Brian S. pp.116. . . . . For this E. E. Austen named a patronymic taxon
A species description is a formal description of a newly discovered species, usually in the form of a scientific paper. Its purpose is to give a clear description of a new species of organism and explain how it differs from species that have be ...
for him, '' G. swynnertoni'' in 1922.
Resistance to trypanosomes
Tsetse flies have an arsenal of immune defenses to resist each stage of the trypanosome infectious cycle, and thus are relatively refractory to trypanosome infection. Among the host flies' defenses is the production of hydrogen peroxide
Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscous than water. It is used as an oxidizer, bleaching agent, and antiseptic, usually as a dilute solution (3% ...
, a reactive oxygen species
In chemistry, reactive oxygen species (ROS) are highly reactive chemicals formed from diatomic oxygen (). Examples of ROS include peroxides, superoxide, hydroxyl radical, singlet oxygen, and alpha-oxygen.
The reduction of molecular oxygen () p ...
that damages DNA. These defenses limit the population of infected flies.
See also
* David Bruce (microbiologist)
Major-General Sir David Bruce (29 May 1855 – 27 November 1931) was an Australian-born British pathologist and microbiologist who made some of the key contributions in tropical medicine. In 1887, he discovered a bacterium, now called ''Bruce ...
* G.D. Hale Carpenter joined the London School of Hygiene and Tropical Medicine
The London School of Hygiene and Tropical Medicine (LSHTM) is a public research university in Bloomsbury, central London, and a member institution of the University of London that specialises in public health and tropical medicine.
The inst ...
, and took the DM in 1913 with a dissertation on the tsetse fly (''Glossina palpalis
Tsetse ( , or ) (sometimes spelled tzetze; also known as tik-tik flies), are large, biting flies that inhabit much of tropical Africa. Tsetse flies include all the species in the genus ''Glossina'', which are placed in their own family, Glos ...
'') and sleeping sickness
African trypanosomiasis, also known as African sleeping sickness or simply sleeping sickness, is an insect-borne parasitic infection of humans and other animals. It is caused by the species ''Trypanosoma brucei''. Humans are infected by two typ ...
. He published
''A Naturalist on Lake Victoria, with an Account of Sleeping Sickness and the Tse-tse Fly''; 1920. T.F. Unwin Ltd, London; Biodiversity Archive
* Muriel Robertson
Muriel Robertson , (8 April 1883 – 14 June 1973) was a Scottish protozoologist and bacteriologist at the Lister Institute, London from 1915 to 1961. She made key discoveries of the life cycle of trypanosomes.
Early life and education
Rober ...
, who conducted early 20th century research on the insect
* Use of DNA in forensic entomology
Forensic entomology has three sub-fields: urban, stored product and medico-criminal entomologies. This article focuses on medico-criminal entomology and how DNA is analyzed with various blood-feeding insects.
Forensic entomology can be an import ...
References
Further reading
*
*
Textbooks
* Buxton, P. (1955). ''The Natural History of Tsetse Flies: An Account of the Biology of the Genus Glossina (Diptera)''. London, UK: H.K. Lewis & Co.
* Ford, J. (1971). ''The Role of the Trypanosomiases in African Ecology''. Oxford, UK: Clarendon Press.
* Glasgow, J. (1963). ''The Distribution and Abundance of Tsetse''. International Series of Monographs on Pure and Applied Biology, No. 20. Oxford, UK: Pergamon Press.
* Leak, S. (1998). ''Tsetse Biology and Ecology: Their role in the Epidemiology and Control of Trypanosomiasis''. New York: CABI Publishing
book site
* Maudlin, I., Holmes, P. H., and Miles, M. A. (2004). ''The Trypanosomiases''. CAB International.
* McKelvey, J., Jr. (1973). ''Man Against Tsetse: Struggle for Africa''. Ithaca, NY: Cornell University Press.
* Mulligan, H. & Potts, W. (1970). ''The African Trypanosomiases''. London: George Allen and Unwin, Ltd.
External links
Programmes and information to assist in the planning and implementation of tsetse control operations
* ttps://web.archive.org/web/20120227040712/http://www.mosquitocatalog.org/files/pdfs/045050-0.pdf ''Tsetse in the Transvaal and Surrounding Territories - An Historical Review'' Claude Fuller (Division of Entomology, 1923)
Leverhulme Trust Tsetse Research Network (LTTRN)
*
STRATEGIC REVIEW OF TRAPS AND TARGETS FOR TSETSE AND AFRICAN TRYPANOSOMIASIS CONTROL - Training in Tropical Diseases
*
{{DEFAULTSORT:Tsetse Fly
Diptera of Africa
Insect vectors of human pathogens
Extant Eocene first appearances
Insects in culture
Flies and humans