Intermediate host

In parasitology, an intermediate host is an organism that is infected with a parasitethat will not reproduce sexually within it, while a definitive host is one in which the parasite reproduces. For example, the broad fish tapewormDiphylobothrium latum develops in fishfor part of its life cycle but only reproduces when it is in a mammaldigestive tract, so its intermediate host is the fish and its definitive host is the mammal.

Because the life cyclesof many parasites are poorly understood, sometimes the "more important" organism is arbitrarily defined as definitive, and this designation may continue even after it is determined to be incorrect. For example, sludge wormsare sometimes considered "intermediate hosts" for whirling disease, even though it is known that the parasite causing the disease reproduces sexually inside them[1].

In Trichinella spiralis, the roundwormthat causes trichinosis, a host has both reproductive adults in its digestive tract and immature juveniles in its muscles, and is therefore considered both an intermediate host and a definitive host.

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It uses material from the http://en.wikipedia.org/wiki/Intermediate+host Wikipedia article Intermediate host.