The Life Cycle of Bilharzia- Simplified

The bilharzia (or schistosomiasis) is a group of parasitic worms that causes all sorts of problems in the human body. The worms most commonly infect humans in Third World countries with poor hygiene and also commonly infect swimmers. Their life cycle is a strange one, taking them in and out of several different species and environments.

Eggs Hatch

The eggs of the schistosomiasis get secreted in human feces. They lay benign until they reach a safe place to hatch. A common hatching ground for their eggs is human feces that has gone through water treatment. Once this water is released, the eggs may hatch. However, they also hatch if feces is left lying on the ground. Once these eggs hatch, they release miracidia, which are the small beings that invade the bodies of snails.

Snails as Hosts

Once inside the snail, the miracidia goes through two generations of sporocysts and the production of cercariae. The cercariae reside in the sporocysts. Once the cysts get too large, they burst. The cercariae then infect snails' bodies and cause them to grow ill. This will eventually kill the snails, at which point the cercarie leaves the bodies of the snails. The cercarie then swim away from the snails and try to find a human host.

Infecting a Human

Once the cercariae find a human, they penetrate the skin. They try to find weak areas in the skin, such as under the arm, in the crotch, or in any cuts or wounds. However, they can penetrate the skin far enough to find the blood stream without any help. Once they are in the human skin, they shed their tails. At this point they become schistosomulae, which is the next step in their life cycle.

Getting to the Veins

After losing its tail, the schistosomulae move through the skin until they reach the veins. They then feed on blood and tissue until they mature. The adults live in the mesenteric venules throughout the body. Different species tend to live in different parts mesenteric venules. They travel through your blood veins and cause great damage to your body, including schistosomiasis, the disease named after the worm. This disease can cause great damage to your internal organs and skin.

Laying the Eggs

Once they reach adulthood, they will mate, and the female will lay her eggs in the small venules of the portal and pervesical systems in your blood system. They will move throughout your blood stream and eventually make their way toward the lumen of the intestine and the bladder. Once they reach these vessels, they are deposited into the intestine and bladder and are secreted. They will then try to make their way back into snails once they hatch.

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