Diphyllobothriasis is an infection caused by the tapeworm Diphyllobothrium latum, which is commonly found in freshwater fish. People can become infected by consuming undercooked or raw fish that contain the larvae of this parasite. Once ingested, the tapeworm can grow in the intestines, leading to various symptoms. Symptoms of diphyllobothriasis may include abdominal discomfort, diarrhea, and weight loss. In some cases, the infection can lead to vitamin B12 deficiency, which may cause anemia. Treatment typically involves medication to eliminate the tapeworm from the body.