Schistosomatidae is a

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

digenetic trematode Digenea (Gr. ''Dis'' – double, ''Genos'' – race) is a class of trematodes in the Platyhelminthes phylum, consisting of parasitic flatworms (known as ''flukes'') with a syncytial tegument and, usually, two suckers, one ventral and one oral. ...

s with complex parasitic life cycles. Immature developmental stages of schistosomes are found in

mollusc Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is esti ...

s and adults occur in

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, ...

s. The best studied group, the

blood fluke ''Schistosoma'' is a genus of trematodes, commonly known as blood flukes. They are parasitic flatworms responsible for a highly significant group of infections in humans termed '' schistosomiasis'', which is considered by the World Health Orga ...

s of the genus ''

Schistosoma ''Schistosoma'' is a genus of trematodes, commonly known as blood flukes. They are parasitic flatworms responsible for a highly significant group of infections in humans termed '' schistosomiasis'', which is considered by the World Health Organ ...

'', infect and cause disease in humans. Other

genera Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nomenclat ...

which are infective to non-human vertebrates can cause mild rashes in humans. Schistosomatids are dioecious (individuals are of separate sexes) which is exceptional with regards to their

phylum In biology, a phylum (; plural: phyla) is a level of classification or taxonomic rank below kingdom and above class. Traditionally, in botany the term division has been used instead of phylum, although the International Code of Nomenclature f ...

Platyhelminthes The flatworms, flat worms, Platyhelminthes, or platyhelminths (from the Greek language, Greek πλατύ, ''platy'', meaning "flat" and ἕλμινς (root: ἑλμινθ-), ''helminth-'', meaning "worm") are a Phylum (biology), phylum of relati ...

, in which most species are hermaphroditic (individuals possess both male and female reproductive systems).

History

The eggs of these parasites were first described by

Theodor Bilharz Theodor Maximilian Bilharz (23 March 1825 – 9 May 1862) was a German physician who made pioneering discoveries in the field of parasitology. His contributions led to the foundation of tropical medicine. He is best remembered as the discoverer ...

, a German pathologist working in

Egypt Egypt ( ar, مصر , ), officially the Arab Republic of Egypt, is a transcontinental country spanning the northeast corner of Africa and southwest corner of Asia via a land bridge formed by the Sinai Peninsula. It is bordered by the Mediter ...

in 1851 who found the eggs during the course of an

autopsy An autopsy (post-mortem examination, obduction, necropsy, or autopsia cadaverum) is a surgical procedure that consists of a thorough examination of a corpse by dissection to determine the cause, mode, and manner of death or to evaluate any di ...

. He wrote two letters to his former teacher

Karl Theodor Ernst von Siebold Prof Karl (Carl) Theodor Ernst von Siebold FRS(For) HFRSE (16 February 1804 – 7 April 1885) was a German physiologist and zoologist. He was responsible for the introduction of the taxa Arthropoda and Rhizopoda, and for defining the taxon Protoz ...

in May and August 1851 describing his findings. von Siebold wrote a paper (published in 1852) summarizing Bilharz's findings. Bilhart's wrote a paper in 1856 describing the worms more fully and he named them ''Distoma haematobium''. Their unusual morphology meant that they could not be comfortably included in ''Distoma'' so in 1856 Meckel von Helmsback created the genus ''Bilharzia'' for them. In 1858 Weinland proposed the name ''Schistosoma'' (

Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

: 'split body') after the male worms' morphology. Despite ''Bilharzia'' having precedence the genus name ''Schistosoma'' was officially adopted by the International Commission on Zoological Nomenclature. In 1898 all the then known species were placed in a subfamily by Stiles and Hassel. This was then elevated to family status by Looss in 1899. Poche in 1907 corrected a grammatical error in the family name. The life cycle was determined by da Silva in 1908.

Evolution

There are a number of different families of blood fluke including the Schistosomatidae. The others include the spirorchiids (turtle parasites) and the sanguinicolids (fish parasites). The Schistosomatidae are considered venous system specialists and their sister group are vascular system generalists - the

Spirorchiidae Spirorchiidae is a family of digenetic trematodes. Infestation by these trematodes leads to the disease spirorchiidiosis. Spirorchiids are mainly parasites of turtles. It has been synonymised with Proparorchiidae Ward, 1921, Spirorchidae Stunka ...

. Schistosomatidae differ from other blood flukes in having separate sexes and

homeothermic Homeothermy, homothermy or homoiothermy is thermoregulation that maintains a stable internal body temperature regardless of external influence. This internal body temperature is often, though not necessarily, higher than the immediate environmen ...

hosts. They have compensated for the reduction in potential reproductive partners by * an increased overdispersion in the vertebrate host * the reduced egg hatching time in the external environment * the formation of permanent pairs mimicking the hermaphroditic condition * the increased longevity in the definitive host * increased fecundity. Colonization of the venous system was made possible by * the evolutionary radiation into terrestrial vertebrates * the increased immunopathology associated with the high, constant body temperature of homeothermic vertebrates. The arterial-dwelling spirorchiids release eggs in the direction of blood flow, resulting in a wide dissemination of eggs within the host. The lower body temperature of

poikilotherm A poikilotherm () is an animal whose internal temperature varies considerably. Poikilotherms have to survive and adapt to environmental stress. One of the most important stressors is temperature change, which can lead to alterations in membrane ...

s is accompanied by a seasonal nature of the

immune response An immune response is a reaction which occurs within an organism for the purpose of defending against foreign invaders. These invaders include a wide variety of different microorganisms including viruses, bacteria, parasites, and fungi which could ...

in these hosts resulting in a quantitatively reduced pathogenesis. Hosts that did succumb to the infection would most likely die in water where eggs could be released by predation, scavengers, or decomposition and develop successfully. Colonization of the venous system by schistosomes required precise egg placement because their eggs are released against the blood flow. Eggs are then sequestered within the portal system (or perivesicular plexus in some species) of homeotherms which restricts egg dispersal but limits the resulting pathology to less sensitive organs. A significant number of eggs may escape into the external environment before a heavily infected host is incapacitated by, or dies from, the infection. The first hosts of the schistosome were birds. Based on their current geographical spread the most likely place of origin of this family is

Asia Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa. Asia covers an area ...

with subsequent spread to

India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the so ...

and

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 ...

. Only one species is known to infect crocodiles - ''

Griphobilharzia amoena ''Griphobilharzia amoena'' is a significant trematode that infect crocodiles such as the Australian freshwater crocodile, ''Crocodylus johnstoni'', located in Darwin, Australia with reported illness in Irian Jaya as well. Platt TR, Blair D, et al ...

''. This species infects the freshwater crocodile ''

Crocodylus johnstoni The freshwater crocodile (''Crocodylus johnstoni''), also known as the Australian freshwater crocodile, Johnstone's crocodile or the freshie, is a species of crocodile endemic to the northern regions of Australia. Unlike their much larger Aus ...

''. Phylogenetic analysis shows that the genus ''

Griphobilharzia ''Griphobilharzia amoena'' is a significant trematode that infect crocodiles such as the Australian freshwater crocodile, ''Crocodylus johnstoni'', located in Darwin, Australia with reported illness in Irian Jaya as well. Platt TR, Blair D, et al ...

'' rather than being a basal schistosome is a relation of the spirorchiids that infect freshwater turtles. It has also shown that the spirorchiids are the closest relations of the schistosoma. An outline of the evolution of the schistosoma is now possible. The ancestral species infected freshwater turtles and the life cycle included gastropod hosts. Some of these species in their turn infected the marine turtles. At some point members of species infecting marine turtles developed the ability to infect birds – most likely waterfowl. This probably occurred somewhere in the Asian continent presumably at or near the coast. The bird species eventually developed the ability to infect mammals. This last development seems to have occurred in

Gondwana Gondwana () was a large landmass, often referred to as a supercontinent, that formed during the late Neoproterozoic (about 550 million years ago) and began to break up during the Jurassic period (about 180 million years ago). The final stages ...

between and .

Taxonomy

The family was created in 1926 by Stiles and Hassel for the ''

'', the

Sanguinicolidae Aporocotylidae is a family of trematodes within the order Diplostomida, which contains species commonly known as fish blood flukes. It contains more than 40 genera, the largest being '' Cardicola''. Species in this family parasite fish in both f ...

and the

. It has since been divided into four subfamilies: Schistosomatinae, Bilharziellinae, Denrobilharziinae and Gigantobilharziinae. In the Gigantobilharziinae the ventral sucker is absent and the female genital pore is medial near the anterior end of the body. In the Bilharziellinae the ventral pore in the female is always posterior to the ventral sucker. Both the Bilharziellinae and the Gigantobilharziinae are found exclusively in birds while the Schistosomatinae are found in both mammals and birds. In the Denrobilharziinae both suckers are absent and the caecum has numerous branches. In this latter family there is one genus ('' Denrdobilharina'') with two species ('' Dendrobilharzina purvulenta'' and '' Dendrobilharzina asicaticus''). There are 12 genera in this family. Of these, seven infect

bird Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweigh ...

s: the others infect

mammal Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...

s including

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, ...

s. There are about 100 known species in this family. The largest genus within the family Schistosomatidae is ''Trichobilharzia'' with over 40 species. The genera are: *Subfamily Bilharziellinae **Genus '' Bilharziella'' - birds ('' Setophaga pensylvanica'', ducks) *Subfamily Denrobilharziinae **Genus '' Dendritobilharzia'' - birds (

duck Duck is the common name for numerous species of waterfowl in the family Anatidae. Ducks are generally smaller and shorter-necked than swans and geese, which are members of the same family. Divided among several subfamilies, they are a form t ...

swan Swans are birds of the family (biology), family Anatidae within the genus ''Cygnus''. The swans' closest relatives include the goose, geese and ducks. Swans are grouped with the closely related geese in the subfamily Anserinae where they form t ...

s) *Subfamily Gigantobilharziinae **''

Gigantobilharzia Schistosomatidae is a family of digenetic trematodes with complex parasitic life cycles. Immature developmental stages of schistosomes are found in molluscs and adults occur in vertebrates. The best studied group, the blood flukes of the genu ...

'' - birds ('' Spinus tristis tristis'') *Subfamily Schistosomatinae **'' Allobilharzia'' - birds (''

Cygnus cygnus The whooper swan ( /ˈhuːpə(ɹ) swɒn/) (''Cygnus cygnus''), also known as the common swan, pronounced ''hooper swan'', is a large northern hemisphere swan. It is the Eurasian counterpart of the North American trumpeter swan, and the type speci ...

'') **''

Austrobilharzia Schistosomatidae is a family of digenetic trematodes with complex parasitic life cycles. Immature developmental stages of schistosomes are found in molluscs and adults occur in vertebrates. The best studied group, the blood flukes of the genus ...

'' - birds (mainly waterfowl) **''

Bivitellobilharzia Schistosomatidae is a family of digenetic trematodes with complex parasitic life cycles. Immature developmental stages of schistosomes are found in molluscs and adults occur in vertebrates. The best studied group, the blood flukes of the genus ' ...

'' - mammals (

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 ...

s) **'' Heterobilharzia'' - mammals (

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) **'' Microbilharzia'' - birds ('' Larus canescens'') **'' Ornithobilharzia'' - mammals (

cattle 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 mal ...

cat The cat (''Felis catus'') is a domestic species of small carnivorous mammal. It is the only domesticated species in the family Felidae and is commonly referred to as the domestic cat or house cat to distinguish it from the wild members of ...

s) **'' Schistomatium'' - mammals (

rodent Rodents (from Latin , 'to gnaw') are mammals of the order Rodentia (), which are characterized by a single pair of continuously growing incisors in each of the upper and lower jaws. About 40% of all mammal species are rodents. They are na ...

s) **''

'' - mammals including humans **''

Trichobilharzia ''Trichobilharzia'' is a genus of trematodes in the family Schistosomatidae. They are worldwide distributed parasites of anatid birds and causative agents of human cercarial dermatitis. Species *'' Trichobilharzia ocellata'' (La Valette, 1855)La ...

'' - birds (mainly waterfowl) ''Orientobilharzia'' differ from ''Schistosoma'' only in the number of

testes A testicle or testis (plural testes) is the male reproductive gland or gonad in all bilaterians, including humans. It is homologous to the female ovary. The functions of the testes are to produce both sperm and androgens, primarily testoster ...

. The four species in this genus have recently (2012) been moved to the genus ''Schistosoma'' on the basis of morphology and molecular studies.Aldhoun JA, Littlewood DT (2012) ''Orientobilharzia'' Dutt & Srivastava, 1955 (Trematoda: Schistosomatidae), a junior synonym of ''Schistosoma'' Weinland, 1858. Syst Parasitol 82(2):81-8. doi: 10.1007/s11230-012-9349-8 The genus name should now be regarded as a junior synonym of ''Schistosoma''. The genera ''Bivitellobilharzia'' and ''Schistosoma'' form a clade in this family. ''Austrobilharzia'' and ''Ornithobilharzia'' are the closest relations of this clade. ''Heterobilharzia'' and ''Schistomatium'' form a separate clade indicating that adaption to mammalian hosts has occurred at least twice. The species in these genera are found in North American mammals suggesting that transmission occurred via birds with subsequent transmission to mammals. The genus ''

'' which infects reptiles has been shown to be a member of the spirorchiid family whose other members infect freshwater turtles. Like the spirorchiids and unlike the schistomes ''Griphobilharzia'' preferentially inhabits the arterial system rather than the venous. This genus was originally grouped with the schistosoma on the basis of the existence of two sexes and other morphological features. ;Notes ''Sinobilharzia'' is a genus that is no longer considered valid.

References

External links

Information portal for NSF funded research on avian schistosome diversity

History

Evolution

Taxonomy

See also

References

External links

Further reading