Opisthorchis species are liver fluke parasites acquired by eating raw or undercooked fish from endemic countries: Thailand, Laos, Cambodia, Viet Nam, and other areas of Asia, Eastern Europe, and the former Soviet Union. While most infected persons are asymptomatic, infections of longer duration can result in severe symptoms and serious illness. Diagnosis is based on identification of eggs in stool specimens with a microscope. Safe and effective medication is available to treat Opisthorchis infections. Adequately freezing or cooking fish will kill the parasite.