Worm infected tissue. Light micrograph of a section through human muscle tissue infested with parasitic Trichinella spiralis nematode worms (large, dark). Humans become infected with these parasites through eating undercooked pork products. The larvae migrate from the intestine to other tissues, where they form cysts (oval), in which they mature. The migration and encystment of these larvae can cause fever and pain brought upon by the host's inflammatory response. In some cases, migration to specific organ tissues can cause myocarditis (inflammation of heart muscle) and encephalitis (acute inflammation of the brain) that can result in death.