Up to nearly 10% of Americans may be infected with brain parasites found in undercooked meat. One example is the brain-invasive pork tapeworm, which is the most common cause of adult-onset epilepsy. Allergenic fish worms found in nearly two-thirds of retail fish tested can trigger allergic reactions in sensitive individuals. There have been migratory skin worms found in undercooked fish (like in sushi).
Cheese may contain mites and maggots and organ meats may contain other worms. Nearly 95% of tested retail U.S. beef (including burgers) has been found to be parasite infested. The meat industry has responded to this problem by feeding arsenic to chickens and turkeys to reduce the parasite load; this arsenic may be linked to increased cancer risk in consumers, and adding bacteria-eating viruses to meat would not help one avoid the brain parasite, toxoplasma, the second leading cause of foodborne disease-related death in the United States. Being bitten by the external parasite, a lone star tick, may result in developing an allergy to meat.