Schistosoma mansoni

Schistosoma mansoni is a significant parasite of humans, a trematode that is one of the major agents of the disease schistosomiasis which is one type of helminthiasis, a neglected tropical disease. The schistosomiasis caused by Schistosoma mansoni is intestinal schistosomiasis.

Schistosomes are atypical trematodes in that the adult stages have two sexes (dioecious) and are located in blood vessels of the definitive host. Most other trematodes are hermaphroditic and are found in the intestinal tract or in organs, such as the liver. The lifecycle of schistosomes includes two hosts: a definitive host (i.e. human) where the parasite undergoes sexual reproduction, and a single intermediate snail host where there are a number of asexual reproductive stages. S. mansoni is named after Sir Patrick Manson, who first identified it in Formosa (now Taiwan).

Morphology of adult schistosomes

Schistosomes, unlike other trematodes, are long and slim worms. The male S. mansoni is approximately 1 cm long (0.6–1.1 cm) and is 0.1 cm wide. It is white, and it has a funnel-shaped oral sucker at its anterior end followed by a second pediculated sucker. The external part of the worm is composed of a double bilayer, which is continuously renewed as the outer layer, known as the membranocalyx, and is shed continuously. The tegument bears a large number of small tubercules. The suckers have small thorns in their inner part as well as in the buttons around them. The male genital apparatus is composed of 6 to 9 testicular masses, situated dorsally. There is one deferent canal beginning at each testicle, which is connected to a single deferent that dilates into a reservatory, the seminal vesicle, located at the beginning of the gynacophoric canal. The copula happens through the coaptation of the male and female genital orifices.