Parasitic Flatworm Life Cycles
The two most prevalent types of parasitic flatworms are blood flukes and tapeworms. Blood flukes exist in countries without adequate water and sewage treatment and infect humans by boring into their skin. Tapeworms are found in most countries and can be contracted by unknowingly ingesting their eggs. These creatures have complex life cycles that ensure their survival.
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Primay Host
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The primary host of a parasitic flatworm is the host body in which the adult lives out its life. For the blood fluke this is often humans who come into contact with untreated water contaminated with infected feces. For the tapeworm, this may be humans, dogs, or farm animals, who are infected by the eggs or larvae by ingesting them.
Secondary Host
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A secondary host is the organism in which the eggs reside. For blood flukes, these hosts are a specific snail species. The snail is used for food by the fluke larvae until they are large enough to burst out and infect a primary host. For the tapeworm, farm animals are often secondary hosts. A tapeworm larvae burrows into the muscle and if a human eats raw or uncooked meat, the tapeworm will invade the human intestine.
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Eggs
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Both the blood fluke and tapeworm lay hundreds of thousands of eggs in the intestines of their primary host. These eggs are not digested and leave the host's body through feces.
Larvae
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Once a blood-fluke egg reaches a water source, it hatches. The tiny larvae bore into a snail and feed off its blood and tissue. The larvae become the adult worm and burst out of the snail's body to swim around looking for a primary host. Tapeworm larvae develop in farm animals or fleas, and are then ingested by the primary host.
Adults
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Adult blood flukes search for a primary host, boring into the host's skin and swimming throughout the circulatory system until they reach the intestines where they absorb blood. The tapeworm attaches itself to the intestinal walls, absorbing nutrients through its skin.
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