Diphyllobothriasis is an infection caused by the Diphyllobothrium species, a type of tapeworm. People typically become infected by consuming raw or undercooked fish that contain the larvae of the tapeworm. Once ingested, the larvae develop into adult tapeworms in the intestines, where they can grow several meters long. Symptoms of diphyllobothriasis may include abdominal discomfort, diarrhea, and weight loss, although some individuals may remain asymptomatic. Diagnosis is usually made through stool tests that identify the presence of tapeworm eggs. Treatment typically involves medication to eliminate the infection.