A common fish-borne parasitic zoonotic infection in humans, Diphyllobothrium latum causes a spectrum of diseases and symptoms that range from mild abdominal discomfort or pain to severe megaloblastic anemia and pernicious anemia. The disease is primarily due to the ingestion of plerocercoid stages (cysts) of fish that contain infectious larvae of D. latum in raw or undercooked fish, although other species of the tapeworm can also cause infection.
Tapeworms in humans can be caused by ingesting the larval stage of any of six different species of tapeworm: Taenia saginata from beef, Taenia solium from pork, Diphyllobothrium latum from fish, Taenia ostertagii from sheep, and Taenia dendromythia from birds. The most common species of tapeworms in humans are Taenia saginata from cattle, Taenia solium from pigs and Diphyllobothrium latum (broad tapeworm) from fish.
The tapeworms infect the intestine and absorb nutrients from food that they feed on. The most serious type of tapeworm disease in humans is megaloblastic anemia, which occurs when the parasite eats too much vitamin B12 and dissociates the vitamin B12-intrinsic factor complex in the gut lumen making vitamin B12 unavailable to the host. This condition can lead to severe neurological damage, including central nervous system degeneration and peripheral neuropathy.
Infection with tapeworms in animals can be prevented by avoiding undercooked meat from infected animals and by washing and cooking all freshwater fish. This is especially important in developing countries where a growing number of people are getting their food from fish markets and restaurants.
Most infected individuals present with a nonspecific illness. They may have abdominal pain or discomfort, diarrhea, nausea, and weakness.
Diagnosis relies on thorough patient history, asking about occupational, hobbies, travel, and eating habits as well as maintaining a high index of suspicion. Laboratory testing is largely nonspecific, but may reveal eosinophilia as well as vitamin B12 deficiency, megaloblastic anemia, and/or pernicious anemia.
Treatment of tapeworms in humans is effective and safe, using the medications praziquantel or niclosamide. Infected people can usually recover from their infections, but if the tapeworms continue to invade the intestinal tract, they may have to be treated again.
The eggs of Diphyllobothrium latum are oval in shape, with a distinct operculum at one pole of the shell. They are light brown in color with dimensions ranging from 67-71 um by 40-51 um.
These eggs can be distinguished from other digenetic trematode eggs by their distinctive appearance. They resemble the eggs of Spirometra spp. but have a rosette-shaped uterus and genital pore with a slit-like bothria.
Proglottids of this tapeworm are usually asymptomatic, but pet owners may observe chains of “spent” proglottids in their cat’s feces. In some cases, these spent proglottids are identifiable with the use of a hand lens.
The worms are easily treated with the medication praziquantel, which has been shown to be highly effective in preventing and treating Diphyllobothrium latum in humans. This medication is available without a prescription and can be purchased over the counter.
