Schistosomatidae is a

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

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

mollusc Mollusca is a phylum of protostome, protostomic invertebrate animals, whose members are known as molluscs or mollusks (). Around 76,000 extant taxon, extant species of molluscs are recognized, making it the second-largest animal phylum ...

s and adults occur in

vertebrate Vertebrates () are animals with a vertebral column (backbone or spine), and a cranium, or skull. The vertebral column surrounds and protects the spinal cord, while the cranium protects the brain. The vertebrates make up the subphylum Vertebra ...

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 Organi ...

s of the genus ''

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

'', infect and cause disease in humans. Other

genera Genus (; : genera ) is a taxonomic rank above species and below family as used in the biological classification of living and fossil organisms as well as viruses. In binomial nomenclature, the genus name forms the first part of the binomial s ...

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 (; : phyla) is a level of classification, or taxonomic rank, that is below Kingdom (biology), kingdom and above Class (biology), class. Traditionally, in botany the term division (taxonomy), division has been used instead ...

Platyhelminthes Platyhelminthes (from the Greek πλατύ, ''platy'', meaning "flat" and ἕλμινς (root: ἑλμινθ-), ''helminth-'', meaning "worm") is a phylum of relatively simple bilaterian, unsegmented, soft-bodied invertebrates commonly called f ...

, 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 o ...

, a German pathologist working in

Egypt Egypt ( , ), officially the Arab Republic of Egypt, is a country spanning the Northeast Africa, northeast corner of Africa and Western Asia, southwest corner of Asia via the Sinai Peninsula. It is bordered by the Mediterranean Sea to northe ...

in 1851 who found the eggs during the course of an

autopsy An autopsy (also referred to as 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 deat ...

. He wrote two letters to his former teacher

Karl Theodor Ernst von Siebold Prof Karl (Carl) Theodor Ernst von Siebold Royal Society of London, 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 d ...

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: 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 of all kno ...

: '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 Stunk ...

. 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 envir ...

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 (Greek ''poikilos'' – 'various', 'spotted', and ''therme'' – 'heat') whose internal temperature varies considerably. Poikilotherms have to survive and adapt to environmental stress. One of the most important s ...

s is accompanied by a seasonal nature of the

immune response An immune response is a physiological reaction which occurs within an organism in the context of inflammation for the purpose of defending against exogenous factors. These include a wide variety of different toxins, viruses, intra- and extracellula ...

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 the largest continent in the world by both land area and population. It covers an area of more than 44 million square kilometres, about 30% of Earth's total land area and 8% of Earth's total surface area. The continent, which ...

with subsequent spread to

India India, officially the Republic of India, is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area; the List of countries by population (United Nations), most populous country since ...

and

Africa Africa is the world's second-largest and second-most populous continent after Asia. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 20% of Earth's land area and 6% of its total surfac ...

. 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 a ...

''. This species infects the freshwater crocodile '' Crocodylus johnstoni''. Phylogenetic analysis shows that the genus '' Griphobilharzia'' 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, sometimes referred to as a supercontinent. The remnants of Gondwana make up around two-thirds of today's continental area, including South America, Africa, Antarctica, Australia (continent), Australia, Zea ...

between and .

Taxonomy

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

'', the Sanguinicolidae 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 (biology), class Aves (), characterised by feathers, toothless beaked jaws, the Oviparity, laying of Eggshell, hard-shelled eggs, a high Metabolism, metabolic rate, a fou ...

s: the others infect

mammal A mammal () is a vertebrate animal of the Class (biology), class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three ...

s including

human Humans (''Homo sapiens'') or modern humans are the most common and widespread species of primate, and the last surviving species of the genus ''Homo''. They are Hominidae, great apes characterized by their Prehistory of nakedness and clothing ...

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 (biology), family Anatidae. Ducks are generally smaller and shorter-necked than swans and goose, geese, which are members of the same family. Divided among several subfam ...

swan Swans are birds of the genus ''Cygnus'' within the family Anatidae. 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 the tribe (biology) ...

s) *Subfamily Gigantobilharziinae **'' Gigantobilharzia'' - birds ('' Spinus tristis tristis'') *Subfamily Schistosomatinae **'' Allobilharzia'' - birds ('' Cygnus cygnus'') **'' Austrobilharzia'' - birds (mainly waterfowl) **'' Bivitellobilharzia'' - mammals (

elephant Elephants are the largest living land animals. Three living species are currently recognised: the African bush elephant ('' Loxodonta africana''), the African forest elephant (''L. cyclotis''), and the Asian elephant ('' Elephas maximus ...

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

raccoon The raccoon ( or , ''Procyon lotor''), sometimes called the North American, northern or common raccoon (also spelled racoon) to distinguish it from Procyonina, other species of raccoon, is a mammal native to North America. It is the largest ...

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

cattle Cattle (''Bos taurus'') are large, domesticated, bovid ungulates widely kept as livestock. They are prominent modern members of the subfamily Bovinae and the most widespread species of the genus '' Bos''. Mature female cattle are calle ...

cat The cat (''Felis catus''), also referred to as the domestic cat or house cat, is a small domesticated carnivorous mammal. It is the only domesticated species of the family Felidae. Advances in archaeology and genetics have shown that the ...

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

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

s) **''

'' - mammals including humans **'' Trichobilharzia'' - birds (mainly waterfowl) ''Orientobilharzia'' differ from ''Schistosoma'' only in the number of

testes A testicle or testis ( testes) is the gonad in all male bilaterians, including humans, and is homologous to the ovary in females. Its primary functions are the production of sperm and the secretion of androgens, primarily testosterone. The ...

. 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 '' Griphobilharzia'' 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