Its internal body is almost fully filled with glycogen particles and vesicles.The cercaria has a characteristic bifurcated tail, classically called furcae (Latin for fork); hence, the name (derived from a Greek word κέρκος, kerkos, meaning tail). The tail is highly flexible and its beating propels the cercaria in water. It is about 0.2 mm long and 47 μm wide, somewhat loosely attached to the main body. The body is pear-shaped and measures 0.24 mm in length and 0.1 mm in width. Its tegument is fully covered with spine. A conspicuous oral sucker is at the apex. As a non-feeding larva, there are no elaborate digestive organs, only oesophagus is distinct. There are three pairs of mucin glands connected to laterally to the oral sucker at the region of the ventral sucker. Physiology
Feeding and nutrition
Developing Schistosoma mansoni worms that have infected their definitive hosts, prior to the sexual pairing of males and females, require a nutrient source in order to properly develop from cercariae to adults. The developing parasites lyse host red blood cells to gain access to nutrients and also makes its own fungi from its waste it is hard to detect; the hemoglobin and amino acids the blood cells contain can be used by the worm to form proteins. While hemoglobin is digested intracellularly, initiated by salivary gland enzymes, iron waste products cannot be used by the worms, and are typically discarded via regurgitation.Kasschau et al.
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.