Schistosoma Intercalatum - Life Cycle

Life Cycle

Schistosoma intercalatum's life cycle is very similar to that of S. haematobium, except for some key differences. To start the life cycle, the human host releases eggs with its feces. In water, the eggs hatch to become miracidia, which penetrate the freshwater snail intermediate host. S. intercalatum has two major strains, each with its own preferred bulinid host. The Zaire strain will use Bulinus africanus, while the Lower Guinea strain will use the extremely common B. forskalii as its intermediate host. The miracidia penetrate the snail tissue, and inside they become sporocysts and multiply. The sporocysts then mature into cercariae inside the snail host and are ready to leave. The cercariae are free-swimming in the surrounding water until they find their definitive host: a human. If there is a small temperature change, the cercariae of S. intercalatum will form concentrated aggregates near the surface of the water. This mechanism for body heat detection of a potential host restricts the formation of viable cercariae to small streams and slow moving bodies of water because of their high sensitivity.

The cercariae penetrate through the human's skin and lose their tail, becoming schistosomulae. The schistosomulae then migrate to the hepatic portal system of the liver to mature into adults. As adults, they make their way to the inferior mesenteric vein and mate, producing thousands of eggs. These eggs migrate down to the mesenteric venules of the colon and form polyps as the eggs attempt to cross into the lumen. S. intercalatum's eggs are specific to the colon, making them unique among the infectious African schistosomes.