tapeworm

any parasitic worm of the subclass Cestoda; these have a flattened bandlike form and numerous species can lodge in the intestines of many animals including human beings. Tapeworms are transmitted to humans in larval form embedded in cysts, in meat or fish that is not properly cooked. In the human body they develop to maturity and attach themselves to the wall of the intestine, where they grow and release eggs. Called also cestode.



Although a large variety of adult tapeworms are sometimes human parasites, only a few infect humans to any great degree. Taenia saginata, the beef tapeworm, and T. solium, the pork tapeworm, are widespread and quite common. Beef tapeworms grow to a length of 4 to 8 meters (12 to 25 feet), and adult pork tapeworms average 2 to 4 meters (6 to 12 feet) in length. Both species release white, egg-containing proglottids, or segments of the body, which make their way to the anus and may be found in clothes or bedding. Diphyllobothrium latum, the fish tapeworm, is found in North America in the Great Lakes region, as well as in Northern Europe and Japan; it may grow as long as 18 meters (60 feet). Hymenolepis nana and H. diminuta are dwarf tapeworms that are common in the tropics and subtropics.

The diagnosis of a tapeworm infection is made when segments of the worm are found in clothing or bedding or when characteristic eggs or segments are found in the stool. Occasionally diarrhea, vague abdominal cramps, flatulence, distention, and nausea occur. Mental deterioration and seizures are rare complications, occurring only when larval forms of the worm invade brain tissue. Tapeworm infection can be prevented by cooking pork, beef, and fish properly. Although most meats and fish are inspected under government supervision, eggs and larvae are not always detectable; the only certain protection is proper cooking.

Once it is inside the body, the tapeworm can be eliminated by specific anthelmintic drugs or surgery. The drug of choice is usually praziquantel, which should be given in a dose large enough to cause the worm to release its hold and pass out through the intestinal tract. If the head is found in the evacuated feces, no further treatment is necessary. However, if the head is not found, the worm could regenerate in two to three months, with segments reappearing in the stools.

Echinococcus granulosus and E. multilocularis differ from other tapeworms in that the adults infect animal hosts and the larval forms are found in humans. The larvae develop in the human intestine, penetrate its wall, and are carried by the lymphatics to various organs of the body where they form slowly growing cysts (hydatid cysts). The liver is the organ most commonly involved. Treatment is by surgical removal of the cyst. Infection with this worm (echinococcosis or hydatid disease) is uncommon in the United States.