Trichinosis is a disease caused by the invasion of the human body by the larval stage of the parasitic nematode worm Trichinella spiralis. Characteristically, humans are infected by eating poorly cooked pork, but infection sometimes follows eating the flesh of other carnivores such as bears or herbivores such as horses. The several varieties of trichinella all have the same life cycle—infection occurs when the larvae, encysted in muscle tissue ("red meat"), are ingested. The cyst wall is dissolved by gastric juices and the larvae are released into the intestine, where they undergo several developmental stages before reaching sexual maturity. Female adult worms may live for some years, continuing to produce newborn larvae that migrate through the intestinal wall and invade many organs and tissues, including the heart, brain, eye, and muscle tissue.
Heavy infection can be lethal or have devastating clinical effects such as seizures, heart attack, or blindness if the brain, heart, or eyes are affected. Light and moderate infection (when only a few cysts are ingested) causes muscle pains, skin rashes, diarrhea, and other symptoms that may be so vague that the condition escapes detection. Sometimes it comes to light only years later when calcium deposits around dead cysts show up on an X-ray. As infection occurs only by ingesting meat containing live larvae, person-to-person transmission is not possible.
Control relies on prevention. Abattoirs must be regularly and rigorously inspected and all suspect meat must be condemned; hunters need to be aware that carnivorous game animals may be infected, and must therefore ensure that meat is thoroughly cooked for long enough to kill any cysts that it may contain.
JOHN M. LAST