Parasite is a plant or animal which lives upon or within another living organism at whose expense it obtains some advantage without compensation. Some of these parasites can be readily seen by the unaided eye, while others are so small they cannot be identified exactly without a microscope. The smallest are the size of a pinhead, while a tapeworm can grow to a length of thirty feet.
Many of these parasites, including the flukes (one of the two types of flatworms), are more prevalent in other countries, especially the tropics, than they are in the United States. The other type of flatworm, the tapeworm, is rare (fewer than 200,000 cases per year in US), but found in the united states and is taken into the body by eating beef, pork, and fish containing this parasite. Inside the intestine, the tapeworm attaches itself to the intestinal wall and proceeds to grow.
Roundworms are also uncommon in this country, is usually in warm climates, like those of tropical and subtropical countries. They include the pinworm, the intestinal roundworm, and the hookworm. Another roundworm which is found in pork causes trichinosis, extremely rare (fewer than 1,000 cases per year in US), a disease in which the parasites eventually get into the patient’s muscles.