Trichinella spiralis is a nematode parasite transmitted through consumption of raw or undercooked pork or wild game meat containing encysted larvae. After ingestion, larvae are released in the small intestine, mature into adult worms, and produce newborn larvae that migrate to striated muscle tissue. Symptoms include myalgia, periorbital edema, fever, and eosinophilia. Diagnosis is based on serology (ELISA) and muscle biopsy. Prevention relies on cooking pork to an internal temperature of 71°C, freezing at -15°C for 3 weeks (though some Trichinella species are freeze-resistant), and proper animal husbandry.
Toxoplasma gondii is a protozoan parasite with cats as the definitive host. Humans become infected by ingesting oocysts from cat feces (contaminated produce, water) or tissue cysts in undercooked meat (particularly lamb and pork). Most infections in immunocompetent adults are asymptomatic, but congenital toxoplasmosis from primary infection during pregnancy can cause severe fetal damage including hydrocephalus, chorioretinitis, and intellectual disability. Prevention includes cooking meat thoroughly, washing produce, wearing gloves during gardening, and avoiding cat litter during pregnancy. No vaccine is available for humans.
Cryptosporidium parvum is a protozoan parasite causing cryptosporidiosis, characterized by watery diarrhea and abdominal cramps. It is transmitted through contaminated water (recreational and drinking water) and produce irrigated with contaminated water. The parasite is highly resistant to chlorine disinfection, making it a common cause of waterborne outbreaks. Detection in stool uses modified acid-fast staining or immunofluorescence, and molecular typing aids source tracking. Ozone and UV irradiation are effective for water treatment, and infected individuals should avoid swimming.
Anisakis simplex is a nematode found in raw or undercooked marine fish (herring, mackerel, salmon, cod, squid). Ingestion of live larvae causes anisakiasis, with larvae penetrating the gastric or intestinal mucosa, causing severe epigastric pain, nausea, and vomiting. Allergic reactions (urticaria, anaphylaxis) to Anisakis allergens can occur even after ingestion of dead larvae. Prevention includes freezing fish at -20°C for at least 24 hours (as required by EU and FDA regulations for raw fish dishes like sushi), or cooking to >60°C. Visual inspection (candling) of fish fillets detects some, but not all, larvae. Parasites are a form of foodborne infection with longer incubation periods than most bacterial infections. Like viruses, they do not multiply in food. Adequate cooking and freezing are effective control measures.
