The most common fish tapeworm in humans is Diphyllobothrium latum, which causes diphyllobothriasis. People become infected by eating undercooked or raw freshwater fish contaminated with tapeworm cysts. The tapeworm can live inside a human intestine for decades and requires more than one host to mature. Symptoms include stomach pain, weight loss, and anemia. Deworming drugs are used to treat the infection, but diatrizoic acid injections may be necessary to remove the entire worm. Freezing fish for 24 hours or cooking it for five minutes at 140 degrees Fahrenheit can prevent infection.
Fish tapeworms include a number of species in the Diphyllobothrium family. The most common fish tapeworm in humans is a species called Diphyllobothrium latum. It causes a disease in humans called diphyllobothriasis. Doctors treat the infection with deworming drugs.
Diphyllobothriasis occurs in populations worldwide. People become infected with fish tapeworm by eating undercooked or raw freshwater fish that is contaminated with tapeworm cysts, which are embryonic tapeworms. The worm can live inside a human intestine for several decades.
The fish tapeworm requires more than one host to mature. They begin life as eggs and mature into six-hooked embryos called coracids. They must be eaten by a crustacean before they can begin the next part of their development and mature into first-instar procercoid larvae.
Small freshwater fish become the second intermediate host of the tapeworm by consuming infested crustaceans. The worm matures into a sparganum or plerocercoid within these fish. The bigger fish consume the smaller fish and eventually the fish could be caught and a human could eat the fish that contains the sparganum. The immature worm grows within the intestine, maturing into a segmented worm that reaches lengths of 25-30 feet (7.62-9.14 m).
Each segment of the worm, or proglottid, produces eggs. A mature fish tapeworm is capable of producing more than a million eggs each day. These eggs leave the body in feces.
Most people who have a fish tapeworm don’t know they are infected. Some individuals may have generalized symptoms such as stomach pain, loss of weight or appetite, and lack of energy, and others suffer from anemia or vitamin B-12 deficiency. Patients might also see proglottids in the stool.
Doctors diagnose diphyllobothriasis by examining a stool sample. They treat the condition with drugs such as praziquantel, niclosamide and albendazole. These drugs don’t always dislodge the worm head from the intestinal wall, and the worm can grow back if the head is still attached. Some doctors use injections of diatrizoic acid to cut off the entire worm so that nothing can grow back.
Raw fish is the main ingredient in many regional cuisines. People who like these dishes can avoid fish tapeworm by freezing fish for 24 hours at a temperature of about minus-4 degrees Fahrenheit (minus-20 degrees Celsius) before preparing the dish. Substituting raw saltwater species for freshwater fish will also help prevent infections, because saltwater fish don’t carry tapeworms. Cooking the fish for about five minutes at 140 degrees Fahrenheit (60 degrees Celsius) will kill the tapeworm roe.
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