There are many species of tapeworm, but only four commonly cause disease in humans: the pork tapeworm, beef tapeworm, fish tapeworm and dwarf tapeworm. All are flatworms, or cestodes, that live as parasites within the human intestinal tract and pass from host to host by depositing their eggs into the host's fecal matter. In places where there is poor hygiene and sanitation, fecal-oral transmission of tapeworm eggs can occur.
Pork Tapeworm
The pork tapeworm, Taenia solium, is the most dangerous tapeworm to humans in that it is the only one that causes the disease cysticercosis. This disease affects the liver, brain and spinal cord, resulting in seizures and other neurologic abnormalities, and in the most extreme cases ends in coma and death. Contrary to popular belief, cysticercosis cannot be acquired by ingesting undercooked pork; while this can cause taeniasis, a parasitic tapeworm infection of the intestine, cysticercosis is caused by direct ingestion of tapeworm eggs, which are contained only in fecal matter, not in meat derived from pigs.
Beef Tapeworm
The beef tapeworm, Taenia saginata, behaves very similarly to the pork tapeworm, and ingestion of undercooked beef containing tapeworm larvae causes taeniasis in much the same way as it does with pork. The main difference is that the eggs of Taenia saginata will not cause cysticercosis upon ingestion, which makes the beef tapeworm considerably less dangerous to humans. However, while typically not lethal, taeniasis can be unpleasant; it frequently entails a number of digestive complaints such as nausea, loss of appetite and stomach pains. Occasionally, egg-containing segments of the tapeworm are spontaneously regurgitated, which then becomes a choking hazard.
Fish Tapeworm
The term "fish tapeworm" actually refers to the genus Diphyllobothrium, which comprises four species found in different geographic locations around the world. They all behave similarly, however, and for practical purposes are considered as a single group. The larvae of these tapeworms reside in fish and crustaceans; these, in turn, will transmit the larvae to a human if ingested raw or undercooked. Once inside a human, the larvae attach to the intestinal wall and grow to adulthood, bathed in the nutrient-rich environment of the host's GI tract. This condition is known as diphyllobothriasis, and these tapeworms, if they are not detected and medically eradicated, will survive up to 10 years and can grow to a length of 36 feet. The life cycle is completed when a fish or crustacean living in water polluted by human feces encounters and ingests a tapeworm egg.
Dwarf Tapeworm
The dwarf tapeworm, Hymenolepis nana, derives its name from its small size in comparison to its cousins. Whereas the fish, pork and beef tapeworms can all grow to sizes exceeding 30 feet, the dwarf tapeworm is typically no bigger than 7 to 10 inches long. It is most commonly found in the Middle East, Southeast Asia, Latin American and rural areas of the southeastern United States. Unlike the other types, person-to-person transmission is common. Toddlers and young children are common hosts due to frequent lapses in fecal-oral hygiene. The dwarf tapeworm can also grow inside rodents and insects, and humans can subsequently contract the tapeworm by eating grain contaminated by these vermin.
References
- "Gastroenterology Clinics of North America"; Tapeworms (cestodiasis); Peter Schantz; September 1996
- "Infectious Disease Clinics of North America"; Taeniasis and cysticercosis; David Botero, et al.; September 1993
- "Journal of Parasitology"; Portrait of human tapeworms; Ana Flisser, et al.; August 2004
