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.
Sex organs, the gonads, are also incompletely separated and are interdependent between sexes. Egg-making organ, the vitelline gland in female does not develop in the absence of male. Male gametes, spermatozoa, are present in the oviduct. In males, there are rudimentary ovaries, oviduct, and oocytes (developing female gametes), as well as vitelline cells. Males also possess the genes for hermaphroditism in flukes. Thus, they are technically hermaphrodites. Egg
The eggs are oval-shaped, measuring 115–175 µm long and 45–47 µm wide, and ~150 µm diameter on average. They have pointed spines towards the broader base on one side, i.e. lateral spines. This is an important diagnostic tool because co-infection with S. haematobium (having a terminal-spined eggs) is common, and they are hard to distinguish. When the eggs are released into the water, a lot of them are immature and unfertilised so that they do not hatch. When the eggs are larger than 160 µm in diameter, they also fail to hatch. Larva
The miracidium (from the Greek word μειράκιον, meirakion, meaning youth) is pear-shaped, and gradually elongates as it ages. It measures about 136 μm long and 55 μm wide. The body is covered by anucleate epidermal plates separated by epidermal ridges. The epidermal cells give off numerous hair-like cilia on the body surface. There are 17–22 epidermal cells. Epidermal plate is absent only at the extreme anterior called apical papilla, or terebratorium, which contains numerous sensory organelles.