What Are Tapeworms?

Tapeworms are relatively uncommon in developed countries, but can infect humans who ingest undercooked meat from animals infected with the parasite.

Tapeworms are a group of segmented flatworms from the taxonomical class Cestoda who find their homes in the intestinal tracts of a wide variety of hosts ranging from humans to arthropods. Humans usually come across the parasite through ingested meat from an infected animal, usually beef, pork, or fish.

The parasite itself ranges from a few centimeters to as many as sixty feet long, depending upon the variety, and survives upon ingested material while making its home on the internal wall of the digestive tract, its hooked head buried into the intestinal tissue. Its eggs are released pre-fertilized into the feces of the host to be spread on to a water source, or to remain in the soil.

When a human ingests a tapeworm, it is usually in the form of a cyst produced in the muscle tissue of an infected animal. Thorough cooking kills tapeworms and their cysts, however, and most meat in developed countries is irradiated or otherwise treated to help prevent transmission of the disease. Raw fish, such as that used in sushi or sashimi, is a high-risk food, as the cyst will escape the preparation process unharmed.

The life cycle of the tapeworm almost always requires at least two hosts, with the adult taking residence in vertebrate hosts. One or more intermediate hosts may be used, these sometimes being tiny arthropods, frequently waterborne, about the size of a flea or gnat. Often, however, the intermediate host will be a pig, cow, or fish, thus permitting transmission to humans. The eggs released by the adult worm in the tract of a final vertebrate host, once they find their way to soil or water lie dormant until ingested by their intermediate host. It is in this host that they hatch into their worm-like larval form, called an oncosphere. From here the oconospheres break the intestinal barrier and enter the circulation, where they find their way to a mass of skeletal muscle tissue, where they form cysts that are consumed by predators, such as humans, which then "hatch" and proceed to bind to the intestinal wall.

Tapeworms are more of a medical nuisance than a real concern, but in massive numbers they can cause weight loss and malnutrition, as they inhibit the operation of digestive enzymes and lower the pH of the intestinal tract in order to retain a higher quantity of digested food. Tapeworm medications are available by prescription or over the counter, and handle the infestation within a few days' time.

As a matter of interest, tapeworms have been used historically, for one by the Romans, as a method of weight loss that permits gluttony. This is, for obvious reasons, not only unrecommended but rather reprehensible. Home tapeworm remedies should be ignored, especially the more fantastical ones involving fasting the patient and then holding warm milk or other food to his face, thus luring the tapeworm out. This is exceedingly silly--tapeworms are not motile, and definitely aren't going to come crawling out your nose for a bowl of milk, whatever you've heard.

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