Tapeworms belong to a group of worms called Cestodes found in Asia and Africa. Humans become infected when they consume eggs and larvae of the tapeworm. Tapeworms infect a variety of hosts that include fish--Diphyllobotrium latum; humans--Hymenolepis nana; cattle--Taenia saginata; and pigs--Taenia solium. They attach to the intestines of humans and animals using a scolex, or head equipped with hooks and suckers. The body is ribbon-shaped and consists of segments called proglottids that contain eggs.
Physical Characteristics
According to the University of South Carolina School of Medicine, the fish tapeworm is the longest tapeworm, measuring between 3 to 10 m in length. The scolex consists of two bothria, or grooves that enable it to attach to the intestinal wall. The body contains approximately 3,000 proglottids. The dwarf tapeworm is the smallest tapeworm, measuring 2.5 to 4 cm long. The scolex is knob-shaped, and has hooks and four suckers. The beef tapeworm measures between 4 to 6 m long. The scolex is pear-shaped with four suckers and no hooks. The body consists of several hundred proglottids. The pork tapeworm is smaller than Taenia saginata, and has a scolex with four suckers and a circular row of hooks.
Life Cycle
According to the U.S. Air Force Public Health Department, the fish tapeworm life cycle has two intermediate hosts. A crustacean called a Copepod consumes the infected feces, and it is then eaten by the second host, a fish. When humans eat undercooked fish, the worm enters the intestine and continues the cycle. Hymenolepis nana does not need an intermediate host, and infects humans and rodents directly when they ingest the eggs. Insects may transfer eggs to humans by eating contaminated feces. Taenia saginata requires an intermediate host which can be either cattle or reindeer. Taenia solium has an intermediate host that may be either wild boar or pig. The eggs enter the body when humans eat undercooked meat; they then hatch and the worms migrate and grow in the intestines where they continue their life cycle.
Distribution
Diphyllobotrium latum is found worldwide, including North America, Russia and countries bordering the Baltic Sea like Sweden and Finland, where eating raw fish is very common. Hymenolepis nana is commonly found throughout the world and is known to infect children. Both taenia species are found throughout the world, but especially in developing countries where food is not properly cooked. Poor hygiene is responsible for the spread of the organisms, according to the U.S. Air Force Public Health Department.
