Host immune defenses are capable of producing superoxide, but these are counterattacked by antioxidant proteins produced by the parasite. Schistosomes have four superoxide dismutases, and levels of these proteins increase as the schistosome grows. Antioxidant pathways were first recognised as a chokepoints for schistosomes, and later extended to other trematodes and cestodes. Targeting of this pathway with different inhibitors of the central antioxidant enzyme thioredoxin glutathione reductase (TGR) results in reduced viability of worms. Decay accelerating factor (DAF) protein is present on the parasite tegument and protects host cells by blocking formation of MAC. In addition, schistosomes have six homologues of human CD59 which are strong inhibitors of MAC. Diagnosis
The presence of S. mansoni is detected by microscopic examination of parasite eggs in stool. A staining method called Kato-Katz technique is used for stool examination. It involves methylene blue-stained cellophane soaked in glycerine or glass slides. A bit costlier technique called formalin-ether concentration technique (FECT) is often used in combination with the direct faecal smear for higher accuracy. Serological and immunological tests are also available. Antibodies and antigens can be detected in the blood using ELISA to identify infection. Adult worm antigens can be detected by indirect haemagglutination assays (IHAs). Polymerase chain reaction (PCR) is also used for detecting the parasite DNA. Circulating cathodic antigen (CCA) in urine can be tested with lateral flow immune-chromatographic reagent strip and point-of-care (POC) tests.Egg detection and immunologic tests are not that sensitive. Polymerase chain reaction (PCR) based testing is accurate and rapid.
In Egypt, 60% of the population in the Northern and Eastern parts of the Nile Delta and only 6% in the Southern part are infected.S. mansoni is commonly found in places with poor sanitation. Because of the parasites fecal-oral transmission, bodies of water that contain human waste can be infectious. Water that contains large populations of the intermediate host snail species is more likely to cause infection. Young children living in these areas are at greatest risk because of their tendency to swim and bathe in cercaria-infected waters longer than adults
. Anyone travelling to the areas described above, and who is exposed to contaminated water, is at risk of schistosomiasis. History
The intermediate hosts Biomphalaria snails are estimated to originate in South America 95–110 million years ago. But the parasites Schistosoma originated in Asia. In Africa, the progenitor species evolved into modern S. mansoni and S. haematobium around 2–5 million years ago.A German physician Theodor Maximillian Bilharz was the first to discover the parasite in 1851, while working at Kasr el-Aini Hospital, a medical school in Cairo. Bilharz recovered them from autopsies of dead soldiers, and noticed two distinct parasites. He described one of them as Distomum haematobium (now S. haematobium) in 1852, but failed to identify the other. In one of his letters to his mentor Karl Theordor von Siebold, he mentioned some of the eggs were different in having terminal spines while some had lateral spines. Terminal-spined eggs are unique to S. haematobium, while lateral spines are found only in S. mansoni.