Beef Tapeworm

Tapeworm adhering to background support, from teaching collection, c. 1930s.
YPM catalog no. 47945

 

Tapeworms are parasitic flatworms that, as adults, live in the digestive cavity of their hosts. As the name implies, they are long ribbon-like organisms and can grow to lengths exceeding 15 feet (5 meters) in humans. Amazingly efficient parasites, tapeworms have no need for a digestive system of their own; instead they simply absorb nutrients from their host's intestinal contents directly through their body wall. People acquire tapeworms from eating undercooked meat or fish that contains the juvenile stage of the parasite.

This tapeworm (above) has been meticulously affixed to a background to show the development of the body. The segments are continually added near the tiny head. Farther along they steadily increase in size and grow into larger egg-bearing segments. Tapeworms are part of a group of animals known as Platyhelminthes, which also includes flatworms. They are very distant relatives of the common earthworm.

The lifecycle of the beef tapeworm.

 

The juvenile stage of a tapeworm is inactive and forms a cyst within the muscle of the intermediate host, in this case cattle. These small cysts are visible to the unaided eye. Meat thus contaminated is referred to as measly. Once ingested, the juvenile emerges and attaches itself by hooks and a sucker on its scolex (head) to the lower intestinal wall of the host. There it grows by adding segments, known as proglottids, incrementally throughout its life. An adult tapeworm can have a thousand or more segments!

Eventually the proglottids become egg-laden or ripe and break away a few at a time. These pass out of the human body in the feces. Cattle feed on infected grass or soil and ingest the eggs. These hatch and the juvenile stage migrates to the muscle or other tissues. The cycle is thereby complete.

Illustration adapted from www.dpd.cc.gov/dpdx/

Plaster model of pork tape worm scolex (head).

 

The parasite's juvenile stage can be killed by cooking meat at temperatures above 133 degrees Fahrenheit (56 degrees Celsius) or freezing below 23 degrees Fahrenheit (–5 degrees Celsius). Beef tapeworms, while unpleasant, are generally not considered dangerous.

Pork tapeworms, however, can be very dangerous because humans can act as the intermediate host. The encysted juvenile stage develops and the ensuing disease, cysticercosis, can lead to seizures and even death if the cysts lodge in the brain.

Magnified image of stained proglottids (on slide above).

YPM catalog no. 105389

 

This microscope slide and the close-up image above show the internal structure of a ripe tapeworm proglottid (body segment). Each mature proglottid has both male and female sex organs (such organisms are known as hermaphrodites) and is capable of producing 100,000 eggs (50,000 per segment in the pork tapeworm).

Photo credit: E. A. Lazo-Wasem.

In a case of tapeworm infection at Yale, this beef tapeworm (Taenia saginata) was removed from a Yale student in March 1896.

 

The collections in the Yale Peabody Museum's Division of Invertebrate Zoology include several specimens of beef tapeworms that were removed from Yale students in March 1896. Most likely all the students ate undercooked (or raw) meat originating from a single source. The students were undoubtedly given an oral anti-helminthic (helminth is Greek for worm) treatment that causes the tapeworm to dislodge and pass out of the body.

Tapeworms were once relatively common in the United States, particularly in rural areas where sanitation was poor and human waste contaminated farmland. Better sanitation and aggressive meat inspection has greatly reduced the risk of parasitism by both the beef and pork tapeworms, but the problem is far from eliminated. Tapeworm infections are steadily increasing in areas where there are growing populations of people migrating to the United States from regions where tapeworms are relatively common. Visit the Division of Invertebrate Zoology to see other items in the Yale Peabody Museum's collections.