by Triana Rathads

Created on: April 22, 2009   Last Updated: April 23, 2009

Tape worms often require a number of different definitive and intermediate hosts to complete their life cycles, often the human can become different types of hosts in this life cycle. Taenia solium is the pork tape worm, and the human is usually the definitive host, in this stage of the tape worms life cycle the tapeworm attaches to the small intestine using four hooked suckers called the scolex. In this stage the tape worm is not an invasive pathogen, it releases its eggs in the form of developed gravid proglottid which pass in the feces, which burst to release eggs. If these eggs are consumed by a pig, the egg develops into a hexacanth which uses its hooks to enter the blood stream, and the larvae develops into a cysticercus within the body of the pig.

The life cycle is complete when humans eat under cooked pork, and the cysticercus can attach to the small intestine to develop onto a tapeworm. This type of life cycle causes no real damage to the human host, although there is a loss of nutrients, which can be followed by weight loss, occurring in highly infected individuals. The real damage which tape worms cause to human health is when the human becomes an intermediate host through accidental consumption of the tape worm eggs. If this happens the human takes the role of the pig in the life cycle, and the tapeworm eggs develop into invasive cysticercus within the human tissue. The cysticercus can develop within the muscles, and even the brain, through travelling through the blood system, this condition is called cysticercosis.

Another tapeworm which uses the human as the primary host, is the beef tapeworm called Taenia rhynchus, however, unlike the pork tape worm, the eggs of this tape worm are not infective to humans, so humans can only be the safer definitive host in this life cycle. There are other tapeworms which can cause serious health problems for a human who has eaten the eggs, such as the tape worm Echinococcus granulosis, the dog and cat tapeworm, where if you have an infected pet, you can consume the eggs accidentally. These eggs hatch, and move to the lungs and the liver within the human, causing a cyst to form around the larvae, this is called a hydatid cyst.

So whilst we all know that tapeworms are worms which live inside our bodies, and that treatment is available, if we do pick up this tame parasite. It should be noted that although it is not in the tapeworms interest to kill us, because we are usually their definitive host, accidental injection of tapeworm eggs can be lethal for humans, and care should be taken to increase hygiene levels around livestock, and pets.

Reference

-Parasitism and the Platyhelminths, by Graham Kearn (1998).

Learn more about this author, Triana Rathads.
Click here to send this author comments or questions.