This occurs in three stages, an initial attachment to the skin, followed by the creeping over the skin searching for a suitable penetration site, often a hair follicle, and finally penetration of the skin into the epidermis using cytolytic secretions from the cercarial post-acetabular, then pre-acetabular glands. On penetration, the head of the cercaria transforms into an endoparasitic larva, the schistosomule. Each schistosomule spends a few days in the skin and then enters the circulation starting at the dermal lymphatics and venules. Here, they feed on blood, regurgitating the haem as hemozoin. The schistosomule migrates to the lungs (5–7 days post-penetration) and then moves via circulation through the left side of the heart to the hepatoportal circulation (>15 days) where, if it meets a partner of the opposite sex, it develops into a sexually mature adult and the pair migrate to the mesenteric veins. Such pairings are monogamous.Male schistosomes undergo normal maturation and morphological development in the presence or absence of a female, although behavioural, physiological and antigenic differences between males from single-sex, as opposed to bisex, infections have been reported. On the other hand, female schistosomes do not mature without a male. Female schistosomes from single-sex infections are underdeveloped and exhibit an immature reproductive system. Although the maturation of the female worm seems to be dependent on the presence of the mature male, the stimuli for female growth and for reproductive development seem to be independent from each other.
They, however, are not frequency used in countries were the disease is common due to the cost of the equipment and the technical experience required to run them. Using a microscope to detect eggs costs about US$0.40 per test well PCR is about $US7 per test as of 2019. Loop-mediated isothermal amplification (LAMP) are being studied as they are lower cost. LAMP testing is not commercially available as of 2019. Treatment
The standard drug for S. mansoni infection is praziquantel at a dose of 40 mg/kg. Oxamniquine is also used. Epidemiology
As of WHO report in 2016, 206.5 million people worldwide are having schistosomiasis due to different species of Schistosoma. More than 105 million people were given medical treatment. S. mansoni is the major species causing an annual death of about 130,000. It is endemic in 55 countries and most prevalent in Africa, the Middle East, the Caribbean, Brazil, Venezuela and Suriname. About 80-85% of schistosomiasis is found in sub-Saharan Africa, where S. haematobium, S. intercalatum and S. mansoni are endemic. Approximately 393 million Africans are at risk of infection from S. mansoni, of which about 55 million are infected at any moment. Annual death due to S. mansoni is about 130,000. The prevalence rate in different countries of Africa are: 73.9% in northern Ethiopia, 37.9% in western Ethiopia, 56% in Nigeria, 60.5% in Kenya, 64.3% in Tanzania, 19.8% in Ghana, and 53.8% in Côte dIvoire.