Schistosomatidae | |
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Egg of Schistosoma mansoni | |
Scientific classification ![]() | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Platyhelminthes |
Class: | Trematoda |
Order: | Diplostomida |
Superfamily: | Schistosomatoidea |
Family: | Schistosomatidae Stiles & Hassall, 1898 |
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 Schistosoma , infect and cause disease in humans. Other genera 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, Platyhelminthes, in which most species are hermaphroditic (individuals possess both male and female reproductive systems).
The eggs of these parasites were first described by Theodor Bilharz, a German pathologist working in Egypt in 1851 who found the eggs during the course of an autopsy. He wrote two letters to his former teacher Karl Theodor Ernst von Siebold 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: '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.
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.
Schistosomatidae differ from other blood flukes in having separate sexes and homeothermic hosts. They have compensated for the reduction in potential reproductive partners by
Colonization of the venous system was made possible by
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 poikilotherms is accompanied by a seasonal nature of the immune response 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 with subsequent spread to India and Africa. [1]
Only one species is known to infect crocodiles - Griphobilharzia amoena . 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. [2] 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. [3] 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 between 120 million years ago and 70 million years ago. [4]
The family was created in 1926 by Stiles and Hassel for the Schistosoma , the Sanguinicolidae and the Spirorchiidae. 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 birds: the others infect mammals including humans. 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:
Orientobilharzia differ from Schistosoma only in the number of testes. The four species in this genus have recently (2012) been moved to the genus Schistosoma on the basis of morphology and molecular studies. [5] 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. [6] 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.
Sinobilharzia is a genus that is no longer considered valid.
Trematoda is a class of flatworms known as flukes or trematodes. They are obligate internal parasites with a complex life cycle requiring at least two hosts. The intermediate host, in which asexual reproduction occurs, is usually a snail. The definitive host, where the flukes sexually reproduce, is a vertebrate. Infection by trematodes can cause disease in all five traditional vertebrate classes: mammals, birds, amphibians, reptiles, and fish.
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 Organization as the second-most socioeconomically devastating parasitic disease, with hundreds of millions infected worldwide.
Digenea is a class of trematodes in the Platyhelminthes phylum, consisting of parasitic flatworms with a syncytial tegument and, usually, two suckers, one ventral and one oral. Adults commonly live within the digestive tract, but occur throughout the organ systems of all classes of vertebrates. Once thought to be related to the Monogenea, it is now recognised that they are closest to the Aspidogastrea and that the Monogenea are more closely allied with the Cestoda. Around 6,000 species have been described to date.
Trematodes are parasitic flatworms of the class Trematoda, specifically parasitic flukes with two suckers: one ventral and the other oral. Trematodes are covered by a tegument, that protects the organism from the environment by providing secretory and absorptive functions.
Schistosoma japonicum is an important parasite and one of the major infectious agents of schistosomiasis. This parasite has a very wide host range, infecting at least 31 species of wild mammals, including 9 carnivores, 16 rodents, one primate (human), two insectivores and three artiodactyls and therefore it can be considered a true zoonosis. Travelers should be well-aware of where this parasite might be a problem and how to prevent the infection. S. japonicum occurs in the Far East, such as China, the Philippines, Indonesia and Southeast Asia.
Trichobilharzia regenti is a neuropathogenic parasitic flatworm of birds which also causes cercarial dermatitis in humans. The species was originally described in 1998 in the Czech Republic and afterwards it was detected also in other European countries, e.g. Denmark, Germany, France, Iceland, Poland, Switzerland, or Russia, and even in Iran. For its unique neurotropic behaviour in vertebrate hosts, the host-parasite interactions are extensively studied in terms of molecular biology, biochemistry and immunology.
Schistosoma mansoni is a water-borne parasite of humans, and belongs to the group of blood flukes (Schistosoma). The adult lives in the blood vessels near the human intestine. It causes intestinal schistosomiasis. Clinical symptoms are caused by the eggs. As the leading cause of schistosomiasis in the world, it is the most prevalent parasite in humans. It is classified as a neglected tropical disease. As of 2021, the World Health Organization reports that 251.4 million people have schistosomiasis and most of it is due to S. mansoni. It is found in Africa, the Middle East, the Caribbean, Brazil, Venezuela and Suriname.
Swimmer's itch, cercarial dermatitis or schistosome dermatitis is a short-term allergic contact dermatitis occurring in the skin of humans that have been infected by water-borne schistosomes, a type of flatworm. It is common in freshwater, brackish and marine habitats worldwide. The incidence of this condition may be increasing, although this may be attributed to better monitoring and reporting. Nevertheless, the condition is considered to be an emerging infectious disease.
Schistosoma intercalatum is a parasitic worm found in parts of western and central Africa. There are two strains: the Lower Guinea strain and the Zaire strain. S. intercalatum is one of the major agents of the rectal form of schistosomiasis, also called bilharzia. It is a trematode, and being part of the genus Schistosoma, it is commonly referred to as a blood-fluke since the adult resides in blood vessels.
Schistosoma malayensis is a schistosome parasite. It was first described in 1988 in Peninsular Malaysia and appears to be a zooenotic infection. The species is named after the country of Malaysia. The natural vertebrate host is van Müller's rat. The intermediate hosts are aquatic snails, Robertsiella kaporenisis. Among Robertsiella kaporenisis are two other Roberstiella species.
Schistosoma indicum is a species of digenetic trematode in the family Schistosomatidae. The parasite is widespread in domestic animals in India and other Asian countries.
Schistosoma ovuncatum is a schistosome parasite, first described in 2002. Its recognition as a new species only occurred when zoologists were re examining specimens originally described in 1984
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. They possess a distinctive tegument that is composed of two lipid bilayers instead of a single bilayer. The double bilayer may be an adaptation to survive the host's immune response.
Adeleorina is a suborder of parasites in the phylum Apicomplexa.
Schistosoma mekongi is a species of trematodes, also known as flukes. It is one of the five major schistosomes that account for all human infections, the other four being S. haematobium, S. mansoni, S. japonicum, and S. intercalatum. This trematode causes schistosomiasis in humans.
Bivitellobilharzia nairi is a species of trematodes, part of the family Schistosomatidae. This is a fairly new identified endoparasite that was found in 1955 by Mudaliar and Ramanujachari, who first recorded the parasite in India. Researchers collected fecal samples of the Indian rhinoceros and were startled to find B. nairi eggs.
Schistosoma bovis is a two-host blood fluke, that causes intestinal schistosomiasis in ruminants in North Africa, Mediterranean Europe and the Middle East. S. bovis is mostly transmitted by Bulinus freshwater snail species. It is one of nine haematobium group species and exists in the same geographical areas as Schistosoma haematobium, with which it can hybridise. S. bovis-haematobium hybrids can infect humans, and have been reported in Senegal since 2009, and a 2013 outbreak in Corsica.
Baracktrema obamai is a species of blood fluke, found in Malaysian freshwater turtles. The discovery prompted the creation of a new genus, Baracktrema. It was discovered in 2015 by a team of American parasitologists led by Thomas R. Platt, and named after U.S. President Barack Obama.
Heterobilharzia is a genus of trematodes in the family Schistosomatidae. The species Heterobilharzia Americana is a parasite of the Southeastern United States and typically found in raccoons. Species of this genus are responsible for Schistosoma in canines. Cercariae found in freshwater may also cause Swimmer's itch in humans.
Schistosoma hippopotami is a species of digenetic trematode that belongs to the genus of blood flukes (Schistosoma) that is found in sub-Saharan Africa. It primarily infects African hippopotamuses and has a more limited host range compared to other Schistosoma species.