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), infecting millions worldwide.

[1][2] Adult flatworms parasitize blood capillaries of either the mesenteries or plexus of the bladder, depending on the infecting species.

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.

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.

[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.

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.

A review of the morphological and molecular data has shown that the differences between these genera are too small to justify their separation.

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.

[26] The parasitic flatworms of Schistosoma cause a group of chronic infections called schistosomiasis known also as bilharziasis.

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.

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.

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.

Von Siebold published a paper in 1852 summarizing Bilharz's findings and naming the worms Distoma haematobium.

[39] In 1858 David Friedrich Weinland proposed the name Schistosoma (Greek: "split body") because the worms were not hermaphroditic but had separate sexes.

[40] Despite Bilharzia having precedence, the genus name Schistosoma was officially adopted by the International Commission on Zoological Nomenclature.

[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.

The life cycle of Schistosoma mansoni was determined by the Brazilian parasitologist Pirajá da Silva (1873-1961) in 1908.

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.