Tapeworms are ribbonlike, segmented flatworms that parasitize humans. The vast majority of tapeworm infections are caused by ingestion of undercooked or raw meat or fish. Tapeworms range in size from a few centimeters to a dozen meters depending on species. The results of tapeworm infection can range from mild discomfort to a severe condition known as cysticerosis.
The fish tapeworm, or Diphyllobothrium latum, is found most frequently in cool lake regions of the world such as Alaska, Canada and the Great Lakes region. People get infected from eating raw or undercooked preparations of freshwater fish. The adult fish tapeworm can grow to be 45 feet in length. People infected with the fish tapeworm are frequently asymptomatic, and most don’t know they are infected until parts of the worm are passed in the stool. Some patients suffer from pernicious anemia due to vitamin B-12 deficiency.
The beef tapeworm, or Taenia saginata, is associated with cattle production. Cattle get infected when grazing on contaminated vegetation. People can become infected with the beef tapeworm by eating raw or undercooked beef. The adult beef tapeworm can grow to a length of 20 feet. Most people infected with the beef tapeworm are asymptomatic. Of any symptoms that do appear, generally abdominal discomfort is the most prevalent.
The pork tapeworm, or Taenia solium, can infect people who eat raw pork or pork that is not fully cooked. The adult worm can survive in the human intestine up to 25 years. Most people show no symptoms when infected with the pork tapeworm. If the eggs of Taenia solium are ingested either through feces, contaminated food or water, or autoinfection, this can cause a serious condition known as cysticercosis. In cysticercosis, the ingested egg hatches and releases the larva, which migrates to other parts of the body, including the eye and the brain (neurocysticercosis). Neurocysticercosis can cause neurological symptoms such as epileptic seizures and psychiatric disturbances.
The accidental ingestion of parasitized insects like fleas and grain beetles can lead to infection with the rat tapeworm, Hymenolepsis diminuta. This relatively small tapeworm causes few to no clinical signs in people.
The dwarf tapeworm, or Hymenolepsis nana, is the only human tapeworm that does not require an intermediate host (pig, cow, flea), and human exposure is hand to mouth. This tapeworm is most frequently seen in young children, with diarrhea a symptom in heavy infections. Both of the Hymenolepsis species of tapeworm grow to a length of 35 to 50 mm.