May 20, 2005

Parasites

The term “parasite” typically refers to worms, or large multicellular organisms, that infect humans. Unlike bacteria that can multiply inside the human body, parasites have a complicated life cycle. Most parasites live part of the life cycle in the human body, but they often reproduce and mature outside the human. Some parasites infect other animals as well as humans. For instance, schistosomiasis spends part of its life in humans and part of its life in snails that live in the river.

The number of persons who are infected with parasites worldwide is enormous. For instance, trichuriasis is a disease caused by infection in the intestines with a nematode, Trichuris trichiura. Over 800 million persons worldwide are infected. In the United States, it is estimated that 2.2 million have the disease. The number of persons infected in the United States is smaller, largely due to the good sanitation. Parasites, either in the form of larvae or eggs, are effectively killed by water treatment. Still, certain parasites are endemic in rural, warm areas, such as the southeastern United States.

In order for a person to be exposed, he or she must have contact with the parasite. This usually occurs in a geographic region where the parasite is endemic. Different parasites have different modes of transmission. For instance, trichinosis is spread by eating contaminated, undercooked pork meat. Schistosomiasis is spread by swimming in water in endemic areas. Schistosomiasis is not endemic in the United States, because the particular snail which hosts the organism does not live in U.S. rivers and creeks. In developing countries, some worm larvae are transmitted through mosquitoes, or even by walking barefoot in soil where larvae are present.

If a doctor suspects a patient has parasites, he may order a stool ova and parasite test (o & p). In this test, the stool is examined with a microscope where larvae or eggs may be observed. A physician may treat a person who has parasites with antibiotics.

Many health professionals consider parasites to be somewhat exotic, since parasites infect mostly persons who have been exposed while in a foreign country--recent immigrants and travelers. Due to the large number of recent immigrants that settle in Houston and the ease of foreign travel, the public health community should be aware of the importance of parasites. Anyone who develops a fever or other signs of illnesses after traveling abroad should call their physician and discuss their travel history as well as their symptoms.

Additional information about parasites can be found at:
http://www.cdc.gov/ncidod/dpd/public/geninfo_find_info.htm.

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