Read this article to learn about the Life Cycle of Schistosoma !
Schistosoma is commonly known as the blood fluke. It is a dioecious parasite commonly found in the human hepatic portal or pelvic veins. Some species are parasites in vein of birds and mammals. It is peculiar in having separate males and female, but the two are found together in pairs (fig. 9.18).
The female, a bit longer than the male, lives in the ventral groove of its male. The male is thicker than the female and permanently carries its female in the gynaecophoric canal. Body surface is rough and spiny, and both have an oral sucker and an acetabulum. There is no pharynx, and the two branches of the intestine reunite in the middle of the body. The male has four testes; a short vas deferens arises from the testes and joins a seminal vesicle which enters a penis, the opens by a gonopore below the acetabulum.
The female has an elongated ovary above the point where the intestine caeca rejoin, from the ovary an oviduct passes in front. In the posterior part of the female are vitelline glands from which a vitelline duct joins the oviduct, the oviduct meets an ootype surrounded by Mehlis, gland. From the ootype arises a straight uterus containing a few capsules, it opens by a female gonopore below the acetabulum.
After fertilization the female leaves the male to lay eggs one at a time in the smaller bold vessel. The capsules lacerate the capillaries and reach the urinary bladder. The capsules hatch into miracidium larvae which enter a freshwater snail and reach its liver and form sporocytes (fig. 9.19).
The first generation of sporocyst may again produce miracidium larva, which then form a second generation of sporocysts, and gives rise to cercaria larvae which have forked tails. The cercariae come out of the snails and swim freely in water, and without encysting they penetrate the human skin with great rapidity during bathing or washing or they may be swallowed by drinking infected water.
Cercariae enter the blood vessels, go to the heart, then lungs, and then to the liver where they grow; after that they enter the hepatic portal or pelvic veins and become sexually mature. The cercariae developing from one egg will produce flukes of only one sex. The females do not mature in a host where no males are present. When a male finds a female, it encloses her in the gynaecophoric canal. Schistosoma causes bladder injuries, bladder stones, skin disease and haematuria which is a disorder of kidneys with discharge of blood.
There are three species of Schistosoma parasitic on human beings:
1. S. haematobium
2. S. mansoni
3. S. japonicum.
Bilharziosis is a tropical illness caused by infection of Schistosoma.