Beef Tapeworm – Large Cestode of Humans
The Natural History of an Intestinal Parasite of People and Cows
Mar 19, 2009
The beef tapeworm, Taenia saginata, is found all over the world — wherever people eat beef — though it is rarely seen in the West today because we have learned how to interrupt its life cycle to avoid infection.
The Life Cycle of Beef Tapeworm
Taenia saginata, one of the largest tapeworms (or cestodes) of humans, requires two hosts to complete its life cycle: the human and the cow. A human with an adult worm in the intestine excretes the worm’s eggs in stool. If the eggs end up outside on the ground, a specific sequence of events will result in more infected humans:
- The eggs are infective to cows (and some other grazing animals). When a cow swallows eggs, they hatch, releasing tiny larvae that leave the cow’s intestines and travel to its muscles.
- Larvae in the muscles form tiny cysts, develop to a stage infective to humans in about two months, and then become dormant.
- If the cow is slaughtered and its meat eaten without being thoroughly cooked, the larvae emerge from the cyst and attach to the wall of the small intestine with a ring of four suckers.
- The attached head of the worm grows, producing a series of rectangular segments, each of which produces thousands of eggs when it matures.
- The parasite can eventually stretch twenty-five metres (82 feet) and it's thought to live a quarter of a century, during which time it releases billions of infective eggs into the environment in its host’s stool.
Symptoms of Beef Tapeworm Infection
Fortunately, having a beef tapeworm typically causes very few symptoms, if any. The host may first discover the worm’s presence when segments are passed in stool or emerge in underclothing. In rare cases infected humans suffer vague symptoms such as hunger or loss of appetite, nausea, weight loss, headaches and dizziness, and diarrhea. Very rarely, the worm causes bowel blockage.
Avoid Beef Tapeworm Infection
It’s relatively easy to avoid acquiring this large intestinal tapeworm, but its life cycle can be interrupted in a number of ways:
- Good sanitation. Animals should never have access to human feces or graze where untreated sewage has contaminated the soil. Sewage treatment must kill worm eggs if the sludge is to be used as fertilizer.
- Meat inspection. Cysts in the cow’s muscles are barely visible to the naked eye, resulting in speckled or “measly” beef.
- Thorough cooking. Beef should be cooked until no pink colour remains. Food handlers should never put unwashed fingers in the mouth, and ensure that any other food to be eaten raw is not contaminated with uncooked beef in the kitchen.
- Freezing beef at -5°C (23°F) or colder for at least a week kills the larvae.
Although the realization that one has a lengthy intestinal companion can be disconcerting, the beef tapeworm usually does little harm and is easily treated with antiparasitic drugs. Even more encouraging, the infection is simple to avoid with an understanding of the parasite’s life cycle. Cultural practices of using untreated human waste as fertilizer, and eating beef rare, however, are likely to ensure the worm’s success in some regions for years to come.
Read more about beef tapeworm.
Related Content:
Sources:
Diagnostic Medical Parasitology 3rd ed. Garcia, Lynn S. and David A. Bruckner. Washington: ASM Press, 1997.
Foundations of Parasitology 6th Ed. Roberts, Larry S. and John Janovy Jr. Boston: McGraw Hill, 2000.
Medical Parasitology 5th ed. Leventhal, Ruth and Russell F. Cheadle. Philadelphia: F.A. Davis, 2002.
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