Schistosoma - Blood FlukesFind The Nastiest Parasites In HumansSchistosoma - Blood FlukesSchistosomiasis (also known as snail fever or bilharzia) is caused by blood flukes from the genusSchistosoma. More than 200 million people are infected worldwide.
Mostly in freshwaters where there aremany snails which are the intermediate host. There are five main species infecting humans: Schistosomamansoni, S. Haematobium, S. Japonicum and two geographically localized species S.intercalatum and S.
Mekongi.Schistosoma requires the use of two hosts to complete its life cycle. Depending on theSchistosoma species their eggs are shed either in the feces or urine of an infected human.
A schistosome is a parasitic trematode worm also known as a blood fluke. The larval forms of the worm live in freshwater snails. What diseases are caused by Schistosomes? Schistosomes cause the disease schistosomiasis also known as Bilharziasis and Snail fever. The parasitic flatworms of Schistosoma cause a group of chronic infections called schistosomiasis known also as bilharziasis. An anti-schistosome drug is a schistosomicide. Species infecting humans. Parasitism of humans by Schistosoma appears to have evolved at.
Eggs cansurvive up to a week in dry land. If the feces end up in water, larvae called miracidia hatch and start findingcertain species of freshwater snails.
When they find a snail they penetrate its foot and transforminto sporocysts (another larval form). These primary sporocysts multiply asexually into secondary sporocysts andtravel to the snail's hepatopancreas.
They multiply asexually producing hundreds of cercariae (another larvalform). (The process from sporocyst to cercaria takes a few months.) Cercariae exit the snail and start waiting inthe water. They can survive about 48 hours in favourable conditions. When they sense that humanskin is near, they quickly swim and attach with suckers. They find a suitable spot (usually a hair follicle) andpenetrate the skin using special enzymes. As they enter they transform into schistosomulae (another larval form).Only head parts enter, they leave tails behind.
Each schistosomula stays a few days in the skin and then enters thebloodstream through dermal lymphatic vessels or blood venules. They travel in the bloodstream to get to specificblood veins. In humans Schistosoma reaches fertility in 6–8 weeks. The newly developed adult females andmales find each other and pair up. Adult blood flukes are 1–2 cm long. Males make a gynaecophoric channel for thelonger and thinner females to reside. The worm pair then travel to rectal or mesenteric veins.
They attach to thevenous wall with oral and ventral suckers and can live for many years. Females lay eggs on the endothelial liningof the venous capillary walls at the rate of 300–3000 eggs per day depending on the Schistosoma species.Some eggs are flushed by circulating blood ending up causing inflammation in organs such as liver or lungs. Mosteggs however travel to the lumen of the intestinal tract ( S. Japonicum and S. Mansoni) and of theureters and bladder ( S. Haematobium), thus exiting the body in the feces or urine.
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Mature eggs producespecial enzymes and can penetrate many membranes such as rectal veins or intestinal wall. The eggs get out of thebody and the cycle starts again.Schistosoma species can migrate around and are not bound to just one location. But each species has apreferred location. For example, S.
Japonicum resides more frequently in the veins that drain the smallintestine. Mansoni is found more often in the veins that drain the large intestine. S.haematobium occurs usually in the venous plexus of bladder, but can also be found in the rectal venules.The first symptoms are a rash or itch during the first few days. Within two months chills,cough, diarrhea, fatigue, fever and muscle aches can occur.
Usually however during the first few weeksschistosomiasis is asymptomatic. The disease is worse for children who can develop anemia, learning difficultiesand malnutrition. After years of infection eggs inflame organs such as the liver, bladder and lungs.
If eggs end upin the brain or spinal cord, they can cause paralysis, seizures or inflammation of the spinal cord.Diagnosis is done from a stool or urine sample by microscopic examination. You need to provideyour health care provider with the samples. Eggs can be present in the feces in infections of allSchistosoma species and in the urine in infections of S. Haematobium and S.
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Japonicum.Tissue biopsy (bladder or rectal biopsy) can also be used in finding eggs, if stool or urine samples are negative.It takes about two months for the parasite to mature into reproducing adult and only after that time will there beeggs present.Schistosomiasis is treated with praziquantel according to the advice of your health careprovider. For infections caused by S. Mansoni oxamniquine can be used in areas where praziquantel is lesseffective.Geographic distribution. Africa: all freshwater in sub-Saharan and southern Africa, also in the Nile River valley in Egypt.
Caribbean: Antigua, Dominican Republic, Guadeloupe, Martinique, Montserrat, Saint Lucia (lowrisk). South America: Brazil, Suriname, Venezuela. Southern China.
Southeast Asia: Cambodia, central Indonesia, Laos, Mekong delta and Philippines. The Middle East: Iran, Iraq, Saudi Arabia, Yemen.Avoid freshwater lakes, rivers or streams in areas where schistosomiasis occurs. Drying yourskin with a towel immediately after swimming might sweep some larval blood flukes away. Swimming in the salty oceanand in chlorinated swimming pools is quite safe. Human feces should be prevented of getting into water to preventsnails from getting infected. In addition to humans Schistosoma species infect many animals such as cats,dogs, horses, pigs, rodents and goats.Also check out the (includes additional pictures).
1858SpeciesSchistosoma is a of, commonly known as blood flukes. They are responsible for a highly significant group of in termed, which is considered by the as the second-most socioeconomically devastating parasitic (after ), with hundreds of millions infected worldwide.Adult flatworms parasitize blood capillaries of either the or of the bladder, depending on the infecting species. They are unique among trematodes and any other flatworms in that they are with distinct between.
Thousands of eggs are released and reach either the bladder or the intestine (according to the infecting species), and these are then excreted in or to. Must then pass through an intermediate snail, before the next larval stage of the parasite emerges that can infect a new mammalian host by directly penetrating the skin. Electron micrograph of an adult male Schistosoma parasite worm. The bar (bottom left) represents a length of 500 μm.The origins of this remain unclear. For many years it was believed that this genus had an African origin, but suggests that the ( S. Edwardiense and S.
Hippopotami) that infect the hippo ( ) could be basal. Since hippos were present in both Africa and Asia during the era the genus might have originated as of hippos. The original hosts for the South East Asian species were probably.Based on the of the host snails it seems likely that the genus evolved in between 70 million years ago and 120 million years ago.The to Schistosoma is a genus of -infecting schistosomes —.The, and cashmere parasite appears to be related to the African schistosomes. This latter species has since been transferred to the genus Schistosoma.Within the haematobium group S. Curassoni appear to be closely related as do S. Leiperi and S. Mansoni appears to have evolved in 0.43–0.30 million years ago.
Mansoni and S. Rodhaini appear to have shared a common ancestor between 107.5-147.6 thousand years ago. 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. 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.
Sinensium appears to have radiated during the. Mekongi appears to have invaded South East in the mid-Pleistocene.
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. Schistosoma turkestanicum is found infecting red deer in. These strains appear to have diverged from those found in. The date of divergence appears to be 270,000 years before present.Taxonomy The genus Schistosoma as currently defined isso revisions are likely. Over twenty species are recognised within this genus.The genus has been divided 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:, and.Haematobium group The nine haematobium group species are:, and.S. Leiperi and S. Matthei appear to be related. Margrebowiei is basal in this group. Guineensis is the sister species to the S.
Curassoni grouping. Intercalatum may actually be a species complex of at least two species. Indicum group The indicum group has three species:,.
This group appears to have evolved during the Pleistocene. All use pulmonate as hosts. Spindale is widely distributed in Asia, but is also found in Africa. They occur in Asia.
Indicum is found in India. The indicum group appears to be the sister clade to the African species. Japonicum group The japonicum group has three species:,.
is a sister to the S. Japonicum group and is found in.
forms a with and is found in northern Thailand. The definitive host is the black rat ( ) and the intermediate host is the snail. This species is known to use snails of the as hosts.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.
Examination of the mitochondria suggests that Schistosoma incognitum may be a species complex. New species As of 2012, four additional species have been transferred to this genus., 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. Schistosoma bomfordi. Schistosoma datta.
Schistosoma harinasutai. Schistosoma turkestanicumHybrids The hybrid S. Haematobium-S.guineenis was observed in Cameroon in 1996. Haematobium could establish itself only after deforestation of the tropical rainforest in next to the endemic S. Guineensis; hybridization led to competitive exclusion of S. Guineensis.In 2003, a S. Rodhaini hybrid was found in snails in western, As of 2009, it had not been found in humans.In 2009, S.
Bovis hybrids were described in northern Senegalese children. The Basin had changed very much since the 1980s after the in Senegal and the 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 e.g. The same hybrid was identified during the 2015 investigation of a schistosomiasis outbreak on, traced to the river.In 2019, a S. Mansoni hybrid was described in a 14-year-old patient with from. Cladogram A based on, and partial (COI) genes shows phylogenic relations of species in the genus Schistosoma:Schistosoma sp.
FromComparison of eggs. Main articles: andThe parasitic flatworms of Schistosoma cause a group of chronic infections called known also as bilharziasis. An anti-schistosome drug is a.Species infecting humans Parasitism of humans by Schistosoma appears to have evolved at least three occasions in both and., a recently described species, is found in. Known intermediate hosts include., commonly referred to as the bladder fluke, originally found in Africa, the, and the basin, was introduced into India during World War II. Freshwater snails of the genus are an important intermediate host for this parasite.
Among final hosts humans are most important. Other final hosts are rarely baboons and monkeys. The usual final hosts are humans.
Other animals can be infected experimentally., whose common name is simply blood fluke, is widespread in and the southwestern region. In this species only affects animals, not humans. Freshwater snails of the genus are an important intermediate host for S. Final hosts are humans and other mammals including cats, dogs, goats, horses, pigs, rats and water buffalo. This species appears to be a rare infection in humans and is considered to be a. The natural vertebrate host is von Muller's rat ( ).
The snail host(s) are Robertsiella species ( R. Kaporensis and R. Silvicola (see Attwood et al.
2005 Journal of Molluscan Studies Volume 71, Issue 4 pp. 379–391)., found in, the lesser, and the. It is also known as Manson's blood fluke or swamp fever. Freshwater snails of the genus are an important intermediate host for this trematode. Among final hosts humans are most important.
Other final hosts are baboons, rodents and raccoons. is related to S. Japonicum and affects both the superior and inferior mesenteric veins. Mekongi differs in that it has smaller eggs, a different intermediate host ( ) and longer prepatent period in the mammalian host. Final hosts are humans and dogs. The snail can also be experimentally infected with this species. Human Schistosomes Scientific NameFirst Intermediate HostEndemic AreaSchistosoma guineensisSchistosoma intercalatumsppSchistosoma haematobiumspp.,Schistosoma japonicumspp.,Schistosoma malayensisspp.Schistosoma mansonispp.,Schistosoma mekongiSpecies infecting other animals , are all parasites of.
and are parasites of the hippo. and are parasites of rodents. Morphology Adult schistosomes share all the fundamental features of the digenea. They have a basic, oral and ventral suckers, a body covering of a, a blind-ending consisting of, and bifurcated; the area between the tegument and alimentary canal filled with a loose network of, and an excretory or osmoregulatory system based on.
Adult worms tend to be 10–20 mm (0.39–0.79 in) long and use from their hosts' for their own circulatory system.Reproduction. Unlike most flatworms, schistosomes are.
The narrow female can be seen emerging from the thicker male's gynecophoral canal below his ventral sucker.Unlike other trematodes, the schistosomes are, i.e., the sexes are separate. The two sexes display a strong degree of, 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. Genome The genomes of Schistosoma haematobium, S. Japonicum and have been reported. History The eggs of these were first seen by, a working in in 1851 who found the eggs of during the course of a.
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. Bilharz wrote a paper in 1856 describing the more fully and he named them Distoma haematobium. Their unusual meant that they could not be comfortably included in Distoma. So in 1856 Meckel von Helmsback created the Bilharzia for them.
In 1858 proposed the name Schistosoma (Greek: 'split body') after the male ' morphology. Despite Bilharzia having precedence, the name Schistosoma was officially adopted by the. The term Bilharzia to describe infection with these parasites is still in use in medical circles. Bilharz also described, but this species was redescribed by in 1907 at the who named it after his teacher. In 1898, all then known species were placed in a by Stiles and Hassel.
This was elevated to family status by in 1899. Poche in 1907 corrected a error in the family name. The was determined by the Brazilian parasitologist (1873-1961) in 1908. In 2009, the genomes of Schistosoma mansoni and were decoded opening the way for new targeted treatments. In particular, the study discovered that the genome of S. Mansoni contained 11,809, including many that produce for breaking down, enabling the parasite to bore through tissue. Mansoni does not have an enzyme to make certain, so it must rely on its host to produce these.
Treatment.