![Anopheles stephensi](https://upload.wikimedia.org/wikipedia/commons/7/7e/Anopheles_stephensi.jpeg)
In
epidemiology
Epidemiology is the study and analysis of the distribution (who, when, and where), patterns and determinants of health and disease conditions in a defined population.
It is a cornerstone of public health, and shapes policy decisions and evidenc ...
, a disease vector is any living agent that carries and transmits an infectious
pathogen
In biology, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ ...
to another living organism;
agents regarded as vectors are organisms, such as
parasites
Parasitism is a Symbiosis, close relationship between species, where one organism, the parasite, lives on or inside another organism, the Host (biology), host, causing it some harm, and is Adaptation, adapted structurally to this way of lif ...
or
microbes
A microorganism, or microbe,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in olde ...
. The first major discovery of a disease vector came from
Ronald Ross
Sir Ronald Ross (13 May 1857 – 16 September 1932) was a British medical doctor who received the Nobel Prize for Physiology or Medicine in 1902 for his work on the transmission of malaria, becoming the first British Nobel laureate, and the f ...
in 1897, who discovered the
malaria
Malaria is a mosquito-borne infectious disease that affects humans and other animals. Malaria causes symptoms that typically include fever, tiredness, vomiting, and headaches. In severe cases, it can cause jaundice, seizures, coma, or death. S ...
pathogen when he dissected a
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 ...
.
Arthropods
Arthropod
Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and Arth ...
s form a major group of pathogen vectors with
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 ...
es,
flies
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 ...
,
sand flies
Sandfly (or sand fly) is a colloquial name for any species or genus of flying, biting, blood-sucking dipteran (fly) encountered in sandy areas. In the United States, ''sandfly'' may refer to certain horse flies that are also known as "greenhea ...
,
lice
Louse ( : lice) is the common name for any member of the clade Phthiraptera, which contains nearly 5,000 species of wingless parasitic insects. Phthiraptera has variously been recognized as an order, infraorder, or a parvorder, as a result o ...
,
flea
Flea, the common name for the order Siphonaptera, includes 2,500 species of small flightless insects that live as external parasites of mammals and birds. Fleas live by ingesting the blood of their hosts. Adult fleas grow to about long, a ...
s,
tick
Ticks (order Ixodida) are parasitic arachnids that are part of the mite superorder Parasitiformes. Adult ticks are approximately 3 to 5 mm in length depending on age, sex, species, and "fullness". Ticks are external parasites, living by ...
s, and
mite
Mites are small arachnids (eight-legged arthropods). Mites span two large orders of arachnids, the Acariformes and the Parasitiformes, which were historically grouped together in the subclass Acari, but genetic analysis does not show clear evid ...
s transmitting a huge number of pathogens. Many such vectors are
haematophagous
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 ...
, which feed on blood at some or all stages of their lives. When the insects feed on blood, the pathogen enters the blood stream of the host. This can happen in different ways.
The ''
Anopheles
''Anopheles'' () is a genus of mosquito first described and named by J. W. Meigen in 1818. About 460 species are recognised; while over 100 can transmit human malaria, only 30–40 commonly transmit parasites of the genus ''Plasmodium'', which c ...
'' mosquito, a vector for
malaria
Malaria is a mosquito-borne infectious disease that affects humans and other animals. Malaria causes symptoms that typically include fever, tiredness, vomiting, and headaches. In severe cases, it can cause jaundice, seizures, coma, or death. S ...
,
filariasis
Filariasis is a parasitic disease caused by an infection with roundworms of the Filarioidea type. These are spread by blood-feeding insects such as black flies and mosquitoes. They belong to the group of diseases called helminthiases.
These par ...
, and various arthropod-borne-viruses (
arbovirus
Arbovirus is an informal name for any virus that is transmitted by arthropod vectors. The term ''arbovirus'' is a portmanteau word (''ar''thropod-''bo''rne ''virus''). ''Tibovirus'' (''ti''ck-''bo''rne ''virus'') is sometimes used to more spe ...
es), inserts its delicate mouthpart under the skin and feeds on its host's blood. The parasites the mosquito carries are usually located in its
salivary gland
The salivary glands in mammals are exocrine glands that produce saliva through a system of ducts. Humans have three paired major salivary glands (parotid, submandibular, and sublingual), as well as hundreds of minor salivary glands. Salivary gla ...
s (used by mosquitoes to anaesthetise the host). Therefore, the parasites are transmitted directly into the host's blood stream. Pool feeders such as the
sand fly
Sandfly (or sand fly) is a colloquial name for any species or genus of flying, biting, blood-sucking dipteran (fly) encountered in sandy areas. In the United States, ''sandfly'' may refer to certain horse flies that are also known as "greenhea ...
and
black fly
A black fly or blackfly (sometimes called a buffalo gnat, turkey gnat, or white socks) is any member of the family Simuliidae of the Culicomorpha infraorder. It is related to the Ceratopogonidae, Chironomidae, and Thaumaleidae. Over 2,200 speci ...
, vectors for pathogens causing
leishmaniasis
Leishmaniasis is a wide array of clinical manifestations caused by parasites of the trypanosome genus ''Leishmania''. It is generally spread through the bite of phlebotomine sandflies, ''Phlebotomus'' and ''Lutzomyia'', and occurs most freq ...
and
onchocerciasis
Onchocerciasis, also known as river blindness, is a disease caused by infection with the parasitic worm ''Onchocerca volvulus''. Symptoms include severe itching, bumps under the skin, and blindness. It is the second-most common cause of blindne ...
respectively, will chew a well in the host's skin, forming a small pool of blood from which they feed. ''
Leishmania
''Leishmania'' is a parasitic protozoan, a single-celled organism of the genus '' Leishmania'' that are responsible for the disease leishmaniasis. They are spread by sandflies of the genus ''Phlebotomus'' in the Old World, and of the genus '' ...
'' parasites then infect the host through the saliva of the sand fly.
Onchocerca
Onchocerca is a genus of parasitic roundworm. It contains one human parasite – ''Onchocerca volvulus'' – which is responsible for the neglected disease Onchocerciasis, also known as "river blindness" because the infected humans tend to live ...
force their own way out of the insect's head into the pool of blood.
Triatomine bugs are responsible for the transmission of a
trypanosome, ''
Trypanosoma cruzi
''Trypanosoma cruzi'' is a species of parasitic euglenoids. Among the protozoa, the trypanosomes characteristically bore tissue in another organism and feed on blood (primarily) and also lymph. This behaviour causes disease or the likelihood of ...
'', which causes
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 ...
. The Triatomine bugs defecate during feeding and the excrement contains the parasites, which are accidentally smeared into the open wound by the host responding to pain and irritation from the bite.
There are several species of
Thrips
Thrips ( order Thysanoptera) are minute (mostly long or less), slender insects with fringed wings and unique asymmetrical mouthparts. Different thrips species feed mostly on plants by puncturing and sucking up the contents, although a few are ...
that act as vectors for over 20 viruses, especially
Tospoviruses
''Orthotospovirus'' is a genus of negative-strand RNA viruses, in the family ''Tospoviridae'' of the order ''Bunyavirales,'' which infects plants. Tospoviruses take their name from the species '' Tomato spotted wilt orthotospovirus'' (TSWV) which ...
, and cause all sorts of
plant diseases
Plant pathology (also phytopathology) is the scientific study of diseases in plants caused by pathogens (infectious organisms) and environmental conditions (physiological factors). Organisms that cause infectious disease include fungus, fung ...
.
Plants and fungi
Some plants and fungi act as vectors for various pathogens. For example, the
big-vein disease of lettuce was long thought to be caused by a member of the fungal division
Chytridiomycota
Chytridiomycota are a division of zoosporic organisms in the kingdom Fungi, informally known as chytrids. The name is derived from the Ancient Greek ('), meaning "little pot", describing the structure containing unreleased zoöspores. Chytrids ...
, namely ''
Olpidium brassicae
''Olpidium brassicae'' is a plant pathogen, it is a fungal obligate parasite. In 1983, the Alsike, Alberta area's clover (which is a major part of horses' diet) was struck by a fungus epidemic of ''Olpidium brassicae'', previously not seen in Ca ...
''. Eventually, however, the disease was shown to be viral. Later it transpired that the virus was transmitted by the
zoospore
A zoospore is a motile asexual spore that uses a flagellum for locomotion. Also called a swarm spore, these spores are created by some protists, bacteria, and fungi to propagate themselves.
Diversity Flagella types
Zoospores may possess one or mo ...
s of the fungus and also survived in the resting spores. Since then, many other fungi in the Chytridiomycota have been shown to vector plant viruses.
Many plant pests that seriously damage important crops depend on other plants, often weeds, to harbour or vector them; the distinction is not always clear. In the case of ''
Puccinia graminis
Stem rust, also known as cereal rust, black rust, red rust or red dust, is caused by the fungus ''Puccinia graminis'', which causes significant disease in cereal crops. Crop species that are affected by the disease include bread wheat, durum whe ...
'' for example, ''
Berberis
''Berberis'' (), commonly known as barberry, is a large genus of deciduous and evergreen shrubs from tall, found throughout Temperateness, temperate and subtropical regions of the world (apart from Australia). Species diversity is greatest in S ...
'' and related genera act as alternate hosts in a cycle of infection of grain.
More directly, when they twine from one plant to another, parasitic plants such as ''
Cuscuta
''Cuscuta'' (), commonly known as dodder or amarbel, is a genus of over 201 species of yellow, orange, or red (rarely green) parasitic plants. Formerly treated as the only genus in the family Cuscutaceae, it now is accepted as belonging in the ...
'' and ''
Cassytha
''Cassytha'' is a genus of some two dozen species of obligately parasitic vines in the family Lauraceae. Superficially, and in some aspects of their ecology, they closely resemble plants in the unrelated genus ''Cuscuta'', the dodders.Weber ...
'' have been shown to convey
phytoplasma
Phytoplasmas are obligate intracellular parasites of plant phloem tissue and of the insect vectors that are involved in their plant-to-plant transmission. Phytoplasmas were discovered in 1967 by Japanese scientists who termed them mycoplasma-lik ...
l and
viral disease
A viral disease (or viral infection) occurs when an organism's body is invaded by pathogenic viruses, and infectious virus particles (virions) attach to and enter susceptible cells.
Structural Characteristics
Basic structural characteristics, s ...
s between plants.
[Haynes, A R. et al. Comparison of two parasitic vines: Dodder (Cuscuta) and Woe vine(Cassytha). Florida Dept Agric & Consumer Services. Division of Plant Industry. Botany Circular No. 30. January/February 1996]
Mammals
Rabies
Rabies is a viral disease that causes encephalitis in humans and other mammals. Early symptoms can include fever and tingling at the site of exposure. These symptoms are followed by one or more of the following symptoms: nausea, vomiting, vi ...
is transmitted through exposure to the saliva or brain tissue of an infected animal. Any
warm-blooded
Warm-blooded is an informal term referring to animal species which can maintain a body temperature higher than their environment. In particular, homeothermic species maintain a stable body temperature by regulating metabolic processes. The onl ...
animal can carry rabies, but the most common vectors are
dog
The dog (''Canis familiaris'' or ''Canis lupus familiaris'') is a domesticated descendant of the wolf. Also called the domestic dog, it is derived from the extinct Pleistocene wolf, and the modern wolf is the dog's nearest living relative. Do ...
s,
skunk
Skunks are mammals in the family Mephitidae. They are known for their ability to spray a liquid with a strong, unpleasant scent from their anal glands. Different species of skunk vary in appearance from black-and-white to brown, cream or ginge ...
s,
raccoon
The raccoon ( or , ''Procyon lotor''), sometimes called the common raccoon to distinguish it from other species, is a mammal native to North America. It is the largest of the procyonid family, having a body length of , and a body weight of ...
s, and
bat
Bats are mammals of the order Chiroptera.''cheir'', "hand" and πτερόν''pteron'', "wing". With their forelimbs adapted as wings, they are the only mammals capable of true and sustained flight. Bats are more agile in flight than most bi ...
s.
World Health Organization and vector-borne disease
The
World Health Organization
The World Health Organization (WHO) is a specialized agency of the United Nations responsible for international public health. The WHO Constitution states its main objective as "the attainment by all peoples of the highest possible level of h ...
(WHO) states that control and prevention of vector-borne diseases are emphasizing "Integrated Vector Management (IVM)", which is an approach that looks at the links between health and environment, optimizing benefits to both.
In April 2014, WHO launched a campaign called “Small bite, big threat” to educate people about vector-borne illnesses. WHO issued reports indicating that vector-borne illnesses affect poor people, especially people living in areas that do not have adequate levels of sanitation, drinking water and housing.
Vector-borne zoonotic disease and human activity
![Disease Vector](https://upload.wikimedia.org/wikipedia/commons/e/ec/Disease_Vector.jpg)
Several articles, recent to early 2014, warn that human activities are spreading vector-borne
zoonotic
A zoonosis (; plural zoonoses) or zoonotic disease is an infectious disease of humans caused by a pathogen (an infectious agent, such as a bacterium, virus, parasite or prion) that has jumped from a non-human (usually a vertebrate) to a human. ...
diseases. Several articles were published in the medical journal ''
The Lancet
''The Lancet'' is a weekly peer-reviewed general medical journal and one of the oldest of its kind. It is also the world's highest-impact academic journal. It was founded in England in 1823.
The journal publishes original research articles, ...
'', and discuss how rapid changes in
land use
Land use involves the management and modification of natural environment or wilderness into built environment such as settlements and semi-natural habitats such as arable fields, pastures, and managed woods. Land use by humans has a long h ...
,
trade globalization Trade globalization is a type of economic globalization and a measure (economic indicator) of economic integration. On a national scale, it loosely represents the proportion of all production that crosses the boundaries of a country, as well as the ...
, and "social upheaval" are causing a resurgence in zoonotic disease across the world.
Examples of vector-borne zoonotic diseases include:
*
Lyme disease
Lyme disease, also known as Lyme borreliosis, is a vector-borne disease caused by the ''Borrelia'' bacterium, which is spread by ticks in the genus ''Ixodes''. The most common sign of infection is an expanding red rash, known as erythema migran ...
*
Plague
Plague or The Plague may refer to:
Agriculture, fauna, and medicine
*Plague (disease), a disease caused by ''Yersinia pestis''
* An epidemic of infectious disease (medical or agricultural)
* A pandemic caused by such a disease
* A swarm of pes ...
*
West Nile virus
West Nile virus (WNV) is a single-stranded RNA virus that causes West Nile fever. It is a member of the family ''Flaviviridae'', from the genus ''Flavivirus'', which also contains the Zika virus, dengue virus, and yellow fever virus. The virus ...
Many factors affect the incidence of vector-borne diseases. These factors include animals hosting the disease, vectors, and people.
Humans can also be vectors for some diseases, such as ''
Tobacco mosaic virus
''Tobacco mosaic virus'' (TMV) is a positive-sense single-stranded RNA virus species in the genus ''Tobamovirus'' that infects a wide range of plants, especially tobacco and other members of the family Solanaceae. The infection causes characteri ...
'', physically transmitting the virus with their hands from plant to plant.
See also
*
Airborne disease
Airborne or aerosol transmission is transmission of an infectious disease through small particles suspended in the air. Infectious diseases capable of airborne transmission include many of considerable importance both in human and veterinary ...
*
Asymptomatic carrier
An asymptomatic carrier is a person or other organism that has become infected with a pathogen, but shows no signs or symptoms.
Although unaffected by the pathogen, carriers can transmit it to others or develop symptoms in later stages of the d ...
*
Fomite
A fomite () or fomes () is any inanimate object that, when contaminated with or exposed to infectious agents (such as pathogenic bacteria, viruses or fungi), can transfer disease to a new host.
Transfer of pathogens by fomites
A fomite is any ina ...
*
Globalization and disease
Globalization, the flow of information, goods, capital, and people across political and geographic boundaries, allows infectious diseases to rapidly spread around the world, while also allowing the alleviation of factors such as hunger and poverty ...
*
Insect vectors of human pathogens
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 of j ...
*
Insect vectors of plant pathogens
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 of j ...
*
VectorBase: genomic database of invertebrate vectors of human pathogens
*
List of diseases caused by insects
Invertebrates are very common vectors of disease. A vector is an organism which spreads disease from one host to another. Invertebrates spread bacterial, viral and protozoan pathogens by two main mechanisms. Either via their bite, as in the case of ...
*
Natural reservoir
In infectious disease ecology and epidemiology, a natural reservoir, also known as a disease reservoir or a reservoir of infection, is the population of organisms or the specific environment in which an infectious pathogen naturally lives and rep ...
*
Waterborne disease
Waterborne diseases are conditions (meaning adverse effects on human health, such as death, disability, illness or disorders) caused by pathogenic micro-organisms that are transmitted in water. These diseases can be spread while bathing, washing, ...
*
2007 Yap Islands Zika virus outbreak
Notes
References
Bibliography
*
*
*
*
*
Pawan, J.L. (1936). "Transmission of the Paralytic Rabies in Trinidad of the Vampire Bat: ''Desmodus rotundus murinus'' Wagner, 1840." ''Annual Tropical Medicine and Parasitol'', 30, April 8, 1936:137–156.
* Pawan, J.L. "Rabies in the Vampire Bat of Trinidad with Special Reference to the Clinical Course and the Latency of Infection." ''
Annals of Tropical Medicine and Parasitology
''Pathogens and Global Health'' is a peer-reviewed medical journal published by Taylor & Francis. It covers tropical diseases, including their microbiology, epidemiology and molecular biology, as well as medical entomology, HIV/AIDS, malaria, an ...
''. Vol. 30, No. 4. December 1936
*
*
External links
WHO page on vector-borne diseases
The National Center for Biotechnology Information, Vector-borne Diseases: Understanding the Environmental, Human Health, and Ecological ConnectionsScience Direct, Current Research in Parasitology and Vector-borne DiseasesScience Direct, Vector-borne Diseases
{{DEFAULTSORT:Vector, Disease
Epidemiology
Parasitology
Disease transmission
Infectious diseases