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Fish parasites ingested by eating raw or partially-cooked fish can cause food poisoning symptoms and other more severe complications. Worms that are found in the flesh or intestines of fish are common examples of fish parasites, and when the fish is consumed raw, the worms and larva pass into the intestines and implant themselves in the body. The three main types of fish parasites are clonorchis sinesis, anisakis, and diphyllobothrium.
Clonorchis sinesis, also known as Oriental liver fluke, is a class of fish parasites that most commonly affects people in Japan, China, Taiwan, and other parts of Asia. The parasite grows inside the walls of the body of a fish and creates a hard shell that protects it from being destroyed by the acidic digestive juices of the human body. After the parasite passes into the intestines, it attaches to the liver and feeds on bile produced by the organ. Stomach pain, jaundice, and fever are common symptoms of clonorchis sinesis. The parasite can reproduce to the point that there is a reduced amount of bile available to the stomach for digestion.
Anisakis is a roundworm that is passed to humans by fish that have ingested shellfish infected with the parasite. The worm attaches to the intestinal wall and sometimes causes white blood cells to form a granuloma. Anisakis is most commonly found in flounder, herring, cod, monkfish, and salmon, and it can cause severe stomach cramps, vomiting, and nausea. If the worm is not naturally passed from the body, it must be surgically removed.
Diphyllobothrium is a tapeworm that attaches to the lining of the intestine in a human after he or she has consumed raw fish that contains larvae of the parasite. The tapeworm will begin to grow, reaching sometimes up to nine feet long (2.74 meters) and will absorb many of the nutrients that the person ingests, causing severe nutritional deficiencies. This can lead to neurological disorders and intestinal problems. Diphyllobothrium will cause diarrhea, vomiting, weight loss, and fatigue, and it can live in the body for nearly 20 years. If diagnosed with a tapeworm, a person will be given a medication that will cause the worm to be passed in the stool.
Prevention of ingesting a fish parasite is the best way to treat food poisoning from fish. Avoid eating raw fish unless it has been frozen prior to preparation. People should make sure to properly clean utensils and counter tops that have been used to prepare fish, and also wash their hands before and after handling raw fish. Food should be properly stored in the refrigerator or freezer in clean containers, and the fish should not be stored in water. Cloth hand towels and sponges should not be used when cleaning or preparing raw fish.
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