Any of a group of parasitic nematodes that usually require two hosts to complete the life cycle: an arthropod and another animal, which is bitten by the arthropod. The female worm produces large numbers of microscopic, active embryos, called microfilariae, that pass into the bloodstream of the primary host. These enter the body of an insect when it bites the infected animal; within the insect the microfilariae grow into larvae, which are passed to an animal the insect bites, where they complete their growth. See also heartworm.
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