Schistosoma

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Schistosoma
Schistosoma mansoni.jpg
Schistosoma mansoni egg
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Platyhelminthes
Class: Trematoda
Order: Diplostomida
Family: Schistosomatidae
Subfamily: Schistosomatinae
Genus: Schistosoma
Weinland, 1858
Species

Schistosoma bomfordi
Schistosoma bovis
Schistosoma curassoni
Schistosoma datta
Schistosoma edwardiense
Schistosoma guineensis
Schistosoma haematobium
Schistosoma harinasutai
Schistosoma hippopotami
Schistosoma incognitum
Schistosoma indicum
Schistosoma intercalatum
Schistosoma japonicum
Schistosoma kisumuensis
Schistosoma leiperi
Schistosoma malayensis
Schistosoma mansoni
Schistosoma margrebowiei
Schistosoma mattheei
Schistosoma mekongi
Schistosoma ovuncatum
Schistosoma nasale
Schistosoma rodhaini
Schistosoma sinensium
Schistosoma spindale
Schistosoma turkestanicum

Contents

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 to be the second-most socioeconomically devastating parasitic disease (after malaria), with hundreds of millions infected worldwide. [1] [2]

Adult flatworms parasitize blood capillaries of either the mesenteries or plexus of the bladder, depending on the infecting species. They are unique among trematodes and any other flatworms in that they are dioecious with distinct sexual dimorphism between male and female. Thousands of eggs are released and reach either the bladder or the intestine (according to the infecting species), and these are then excreted in urine or feces to fresh water. Larvae must then pass through an intermediate snail host before the next larval stage of the parasite emerges that can infect a new mammalian host by directly penetrating the skin.

Evolution

Electron micrograph of an adult male Schistosoma parasite worm. The bar (bottom left) represents a length of 500 mm. Schistosoma 20041-300.jpg
Electron micrograph of an adult male Schistosoma parasite worm. The bar (bottom left) represents a length of 500 μm.

The origins of this genus remain unclear. For many years it was believed that this genus had an African origin, but DNA sequencing suggests that the species (S. edwardiense and S. hippopotami) that infect the hippo ( Hippopotamus amphibius ) could be basal. Since hippos were present in both Africa and Asia during the Cenozoic era, the genus might have originated as parasites of hippos. [3] The original hosts for the South East Asian species were probably rodents. [4]

Based on the phylogenetics of the host snails it seems likely that the genus evolved in Gondwana between 70  million years ago and 120  million years ago. [5]

The sister group to Schistosoma is a genus of elephant-infecting schistosomes — Bivitellobilharzia .

The cattle, sheep, goat and cashmere goat parasite Orientobilharzia turkestanicum appears to be related to the African schistosomes. [6] [7] This latter species has since been transferred to the genus Schistosoma. [8]

Within the haematobium group S. bovis and S. curassoni appear to be closely related as do S. leiperi and S. mattheei.[ citation needed ]

S. mansoni appears to have evolved in East Africa 0.43–0.30 million years ago.[ citation needed ]

S. mansoni and S. rodhaini appear to have shared a common ancestor between 107.5 and 147.6 thousand years ago. [9] This period overlaps with the earliest archaeological evidence for fishing in Africa. It appears that S. mansoni originated in East Africa and experienced a decline in effective population size 20-90 thousand years ago before dispersing across the continent during the Holocene. This species was later transmitted to the Americas by the slave trade.

S. incognitum and S. nasale are more closely related to the African species rather than the japonicum group.[ citation needed ]

S. sinensium appears to have radiated during the Pliocene. [10] [11]

S. mekongi appears to have invaded South East Asia in the mid-Pleistocene. [4]

Estimated speciation dates for the japonicum group: ~3.8 million years ago for S. japonicum/South East Asian schistosoma and ~2.5 million years ago for S. malayensis/S. mekongi. [4]

Schistosoma turkestanicum is found infecting red deer in Hungary. These strains appear to have diverged from those found in China and Iran. [12] The date of divergence appears to be 270,000 years before present.

Taxonomy

The genus Schistosoma as currently[ when? ] defined is paraphyletic,[ citation needed ] so revisions are likely. Over twenty species are recognised within this genus.

The genus has been divided [ citation needed ] into four groups: indicum, japonicum, haematobium and mansoni. The affinities of the remaining species are still being clarified.

Thirteen species are found in Africa. Twelve of these are divided into two groups—those with a lateral spine on the egg (mansoni group) and those with a terminal spine (haematobium group).

Mansoni group

The four mansoni group species are: S. edwardiense , S. hippotami , S. mansoni and S. rodhaini .

Haematobium group

The nine haematobium group species are: S. bovis , S. curassoni , S. guineensis , S. haematobium , S. intercalatum , S. kisumuensis , S. leiperi , S. margrebowiei and S. mattheei .

S. leiperi and S. matthei appear to be related. [13] S. margrebowiei is basal in this group. [14] S. guineensis is the sister species to the S. bovis and S. curassoni grouping. S. intercalatum may actually be a species complex of at least two species. [15] [16]

Indicum group

The indicum group has three species: S. indicum , S. nasale and S. spindale . This group appears to have evolved during the Pleistocene. All use pulmonate snails as hosts. [17] S. spindale is widely distributed in Asia, but is also found in Africa.[ citation needed ] They occur in Asia and India. [18]

S. indicum is found in India and Thailand.[ citation needed ]

The indicum group appears to be the sister clade to the African species. [19]

Japonicum group

The japonicum group has five species: S. japonicum , S. malayensis and S. mekongi , S. ovuncatum and S. sinensium and these species are found in China and Southeast Asia. [20]

S. ovuncatum forms a clade with S. sinensium and is found in northern Thailand. The definitive host is unknown and the intermediate host is the snail Tricula bollingi . This species is known to use snails of the family Pomatiopsidae as hosts. [20]

S. incognitum appears to be basal in this genus. It may be more closely related to the African-Indian species than to the Southeast Asian group. This species uses pulmonate snails as hosts.[ citation needed ] Examination of the mitochondria suggests that Schistosoma incognitum may be a species complex. [21]

New species

As of 2012, four additional species have been transferred to this genus., [8] previously classified as species in the genus Orientobilharzia. Orientobilharzia differs from Schistosoma morphologically only on the basis of the number of testes. A review of the morphological and molecular data has shown that the differences between these genera are too small to justify their separation. The four species are

Hybrids

The hybrid S. haematobium-S.guineenis was observed in Cameroon in 1996. S. haematobium could establish itself only after deforestation of the tropical rainforest in Loum next to the endemic S. guineensis; hybridization led to competitive exclusion of S. guineensis. [22]

In 2003, a S. mansoni-S. rodhaini hybrid was found in snails in western Kenya, [23] As of 2009, it had not been found in humans. [24]

In 2009, S. haematobium–S. bovis hybrids were described in northern Senegalese children. The Senegal River Basin had changed very much since the 1980s after the Diama Dam in Senegal and the Manantali Dam in Mali had been built. The Diama dam prevented ocean water to enter and allowed new forms of agriculture. Human migration, increasing number of livestock and sites where human and cattle both contaminate the water facilitated mixing between the different schistosomes in N'Der, for example. [24] The same hybrid was identified during the 2015 investigation of a schistosomiasis outbreak on Corsica, traced to the Cavu river. [25]

In 2019, a S. haematobium–S. mansoni hybrid was described in a 14-year-old patient with hematuria from Côte d'Ivoire. [26]

Cladogram

A cladogram based on 18S ribosomal RNA, 28S ribosomal RNA, and partial cytochrome c oxidase subunit I (COI) genes shows phylogenic relations of species in the genus Schistosoma: [27]

Comparison of eggs

Geographical distribution

Geographical areas associated with schistosomiasis by the World Health Organization as of January 2017 include in alphabetical order: Africa, Brazil, Cambodia, the Caribbean, China, Corsica, Indonesia, Laos, the Middle East, the Philippines, Suriname, and Venezuela. [28] There had been no cases in Europe since 1965, until an outbreak occurred on Corsica. [25]

Schistosomiasis

The parasitic flatworms of Schistosoma cause a group of chronic infections called schistosomiasis known also as bilharziasis. [29] An anti-schistosome drug is a schistosomicide.

Species infecting humans

Parasitism of humans by Schistosoma appears to have evolved at least three occasions in both Asia and Africa.

Human Schistosomes
Scientific NameFirst Intermediate HostEndemic Area
Schistosoma guineensis Bulinus forskalii West Africa
Schistosoma intercalatum Bulinus spp Africa
Schistosoma haematobium Bulinus spp. Africa, Middle East
Schistosoma japonicum Oncomelania spp. China, East Asia, Philippines
Schistosoma malayensis Robertsiella spp. Southeast Asia
Schistosoma mansoni Biomphalaria spp. Africa, South America, Caribbean, Middle East
Schistosoma mekongi Neotricula aperta Southeast Asia

Species infecting other animals

Schistosoma indicum , Schistosoma nasale , Schistosoma spindale , Schistosoma leiperi are all parasites of ruminants.[ citation needed ]

Schistosoma edwardiense and Schistosoma hippopotami are parasites of the hippo.[ citation needed ]

Schistosoma ovuncatum and Schistosoma sinensium are parasites of rodents.[ citation needed ]

Morphology

Adult schistosomes share all the fundamental features of the digenea. They have a basic bilateral symmetry, oral and ventral suckers, a body covering of a syncytial tegument, a blind-ending digestive system consisting of mouth, esophagus and bifurcated caeca; the area between the tegument and alimentary canal filled with a loose network of mesoderm cells, and an excretory or osmoregulatory system based on flame cells. Adult worms tend to be 10–20 mm (0.39–0.79 in) long and use globins from their hosts' hemoglobin for their own circulatory system.

Reproduction

Unlike other flatworms, schistosomes are gonochoristic. The narrow female can be seen emerging from the thicker male's gynecophoral canal below his ventral sucker. Schistosome Parasite SEM.jpg
Unlike other flatworms, schistosomes are gonochoristic. The narrow female can be seen emerging from the thicker male's gynecophoral canal below his ventral sucker.

Unlike other trematodes and basically all other flatworms, the schistosomes are dioecious, i.e., the sexes are separate. The two sexes display a strong degree of sexual dimorphism, and the male is considerably larger than the female. The male surrounds the female and encloses her within his gynacophoric canal for the entire adult lives of the worms. As the male feeds on the host's blood, he passes some of it to the female. The male also passes on chemicals which complete the female's development, whereupon they will reproduce sexually. Although rare, sometimes mated schistosomes will "divorce", wherein the female will leave the male for another male. The exact reason is not understood, although it is thought that females will leave their partners to mate with more genetically distant males. Such a biological mechanism would serve to decrease inbreeding, and may be a factor behind the unusually high genetic diversity of schistosomes. [31]

Genome

The genomes of Schistosoma haematobium, S. japonicum and S. mansoni have been reported. [32] [33] [34] [35]

History

The eggs of these parasites were first seen by Theodor Maximilian Bilharz, a German pathologist working in Egypt in 1851 who found the eggs of Schistosoma haematobium during the course of a post mortem. He wrote two letters to his former teacher von Siebold in May and August 1851 describing his findings. Von Siebold published a paper in 1852 summarizing Bilharz's findings and naming the worms Distoma haematobium. [36] Bilharz wrote a paper in 1856 describing the worms more fully. [37] Their unusual morphology meant that they could not be comfortably included in Distoma. So in 1856 Meckel von Helmsback (de) created the genus Bilharzia for them. [38] In 1858 David Friedrich Weinland proposed the name Schistosoma (Greek: "split body") because the worms were not hermaphroditic but had separate sexes. [39] Despite Bilharzia having precedence, the genus name Schistosoma was officially adopted by the International Commission on Zoological Nomenclature. The term Bilharzia to describe infection with these parasites is still in use in medical circles.[ citation needed ]

Bilharz also described Schistosoma mansoni , but this species was redescribed by Louis Westenra Sambon in 1907 at the London School of Tropical Medicine who named it after his teacher Patrick Manson. [40]

In 1898, all then known species were placed in a subfamily by Stiles and Hassel. This was elevated to family status by Looss in 1899. Poche in 1907 corrected a grammatical error in the family name. The life cycle of Schistosoma mansoni was determined by the Brazilian parasitologist Pirajá da Silva (1873-1961) in 1908. [41]

In 2009, the genomes of Schistosoma mansoni and Schistosoma japonicum were decoded [32] [33] opening the way for new targeted treatments. In particular, the study discovered that the genome of S. mansoni contained 11,809 genes, including many that produce enzymes for breaking down proteins, enabling the parasite to bore through tissue. Also, S. mansoni does not have an enzyme to make certain fats, so it must rely on its host to produce these. [42]

Treatment

Praziquantel [43]

Related Research Articles

<span class="mw-page-title-main">Schistosomiasis</span> Human disease caused by parasitic worms called schistosomes

Schistosomiasis, also known as snail fever, bilharzia, and Katayama fever, is a disease caused by parasitic flatworms called schistosomes. The urinary tract or the intestines may be infected. Symptoms include abdominal pain, diarrhea, bloody stool, or blood in the urine. Those who have been infected for a long time may experience liver damage, kidney failure, infertility, or bladder cancer. In children, it may cause poor growth and learning difficulties.

<span class="mw-page-title-main">Trematoda</span> Class of parasitic flatworms

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.

<span class="mw-page-title-main">Schistosomatidae</span> Family of flukes

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.

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 nine 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.

<i>Schistosoma mansoni</i> Species of fluke

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.

<i>Biomphalaria</i> Genus of freshwater snails

Biomphalaria is a genus of air-breathing freshwater snails, aquatic pulmonates belonging to the family Planorbidae, the ram's horn snails and their allies.

<i>Schistosoma intercalatum</i> Species of fluke

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.

<i>Schistosoma haematobium</i> Species of fluke

Schistosoma haematobium is a species of digenetic trematode, belonging to a group (genus) of blood flukes (Schistosoma). It is found in Africa and the Middle East. It is the major agent of schistosomiasis, the most prevalent parasitic infection in humans. It is the only blood fluke that infects the urinary tract, causing urinary schistosomiasis, and is the leading cause of bladder cancer. The diseases are caused by the eggs.

<i>Schistosoma malayensis</i> Species of fluke

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.

<span class="mw-page-title-main">Theodor Bilharz</span> German physician

Theodor Maximilian Bilharz 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 of the blood fluke Schistosoma haematobium, the causative parasite of bloody urine (haematuria) known since ancient times in Egypt. The parasite, as the cause of bladder cancer, is declared by the International Agency for Research on Cancer as Group 1 carcinogen. The infection is known by an eponymous term bilharzia or bilharziasis, as well as by schistosomiasis.

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.

<span class="mw-page-title-main">Schistosomiasis vaccine</span>

A Schistosomiasis vaccine is a vaccine against Schistosomiasis, a parasitic disease caused by several species of fluke of the genus Schistosoma. No effective vaccine for the disease exists yet. Schistosomiasis affects over 200 million people worldwide, mainly in rural agricultural and peri-urban areas of the third world, and approximately 10% suffer severe health complications from the infection. While chemotherapeutic drugs, such as praziquantel, oxamniquine and metrifonate both no longer on the market, are currently considered safe and effective for the treatment of schistosomiasis, reinfection occurs frequently following drug treatment, thus a vaccine is sought to provide long-term treatment. Additionally, experimental vaccination efforts have been successful in animal models of schistosomiasis.

<i>Biomphalaria glabrata</i> Species of mollusc

Biomphalaria glabrata is a species of air-breathing freshwater snail, an aquatic pulmonate gastropod mollusk in the family Planorbidae, the ram's horn snails.

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.

<i>Biomphalaria straminea</i> Species of gastropod

Biomphalaria straminea is a species of air-breathing freshwater snail, an aquatic pulmonate gastropod mollusk in the family Planorbidae, the ram's horn snails.

<i>Biomphalaria sudanica</i> Species of mollusc

Biomphalaria sudanica is a species of air-breathing freshwater snail, an aquatic pulmonate gastropod belonging to the family Planorbidae, the ram's horn snails. Biomphalaria sudanica has a discoidal, brown shell with an approximate shell diameter of 9–11mm. Biomphalaria sudanica is a medically important pest, due to it being an intermediate host of the intravascular trematode genus, Schistosoma.

<i>Schistosoma spindale</i> Species of fluke

Schistosoma spindale is a species of digenetic trematode in the family Schistosomatidae. It causes intestinal schistosomiasis in the ruminants.

<span class="mw-page-title-main">Bivitellobilharzia nairi</span> Species of fluke

Bivitellobilharzia nairi is a species of trematodes, part of the family Schistosomatidae. This is a fairly new identified endoparasite that was found in 1945 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.

Carcinogenic parasites are parasitic organisms that depend on other organisms for their survival, and cause cancer in such hosts. Three species of flukes (trematodes) are medically-proven carcinogenic parasites, namely the urinary blood fluke, the Southeast Asian liver fluke and the Chinese liver fluke. S. haematobium is prevalent in Africa and the Middle East, and is the leading cause of bladder cancer. O. viverrini and C. sinensis are both found in eastern and southeastern Asia, and are responsible for cholangiocarcinoma. The International Agency for Research on Cancer declared them in 2009 as a Group 1 biological carcinogens in humans.

References

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  29. ↑ Britannica Concise Encyclopedia 2007
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  31. ↑ "Even Blood Flukes Get Divorced - The Loom". The Loom. 2008-10-08. Retrieved 2016-05-24.
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  36. ↑ Bilharz T, von Siebold CT (1852). "Ein Beitrag zur Helminthographia humana ..." [A contribution to the literature on helminths [afflicting] humans ...]. Zeitschrift für wissenschaftliche Zoologie (in German). 4: 53–76. See: "2. Distomum Haematobium Bilh.", pp. 59–62.
  37. ↑ Bilharz T (1856). "Distomum haematobium und sein Verhältnis zu gewissen pathologischen Veränderungen der menschlichen Harnorgane" [Distomum haematobium and its relation to certain pathological changes of the human urinary organs]. Wiener Medizinische Wochenschrift (in German). 6: 49–52, 65–68.
  38. ↑ von Hemsbach JH, Billroth T (1856). Mikrogeologie: Ueber die Concremente im thierischen Organismus [Microgeology: On the concretions in animal organisms] (in German). Berlin, (Germany): Georg Reimer. p. 114. ISBN   9783112028636. From p. 114: "Bilharz beschrieb zuerst in v. Siebold u. Kölliker's Zeitschr. f. Zoologie 1852. einen neuen Eingeweidewurm des Menschen, sehr den Distomen ähnlich und deshalb von ihm Distomum haematobium genannt. Der Art-Name ist sehr bezeichnend, der Gattungs-Name darf nicht füglich Distoma bleiben, ist durch Bilharzia zu ersetzen." (Bilharz first described in von Siebold and Kölliker's Journal for [Scientific] Zoology of 1852 a new intestinal worm of humans, [which is] very similar to the Distoma and therefore was named by him Distomum haematobium. The species name is very characteristic; the genus name may not justifiably remain Distoma; [it] is to be replaced by Bilharzia.)
  39. ↑ Weinland DF (1858). Human Cestoides: An Essay on the Tapeworms of Man ... Cambridge, Massachusetts, USA: Metcalfe and Company. p. 87. See footnote †.
  40. ↑ See:
  41. ↑ See:
    • da Silva P (August 1908). "Contribuição para o estudo da Schistosomíase" [Contribution to the study of schistosomiasis in Bahia]. Brazil-Medico (in Portuguese). 22: 281–282.
    • da Silva P (December 1908). "Contribuição para o estudo da Schistosomíase na Bahia. Dezesseis observações" [Contribution to the study of schistosomiasis in Bahia. Sixteen observations.]. Brazil-Medico (in Portuguese). 22: 441–444.
    • da Silva P (1908). "Contribuição para o estudo da Schistosomíase. Vinte observações" [Contribution to the study of schistosomiasis in Bahia. Twenty observations.]. Brazil-Medico (in Portuguese). 22: 451–454.
    • da Silva P (1908). "La schistosomose à Bahia" [Schistosomiasis in Bahia]. Archives de Parasitologie (in French). 13: 283–302.
    • da Silva P (1909). "Contribution to the study of schistosomiasis in Bahia, Brazil". Journal of Tropical Medicine and Hygiene. 12: 159–164.
  42. ↑ "Killer parasites' genes decoded". BBC News. July 16, 2009. Retrieved 2009-07-16.
  43. ↑ "Parasites - Schistosomiasis". Centers for Disease Control and Prevention. U.S. Department of Health & Human Services. 28 October 2020.

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