FAMILY MEDICINE® COLUMN
By John C. Wolf, D.O.
Associate Professor of Family Medicine®
Ohio University College of Osteopathic Medicine

NOT ALL WORMS GOOD FOR FISHING

Question: I know that humans can have pinworms, stomach worms and tapeworms. How many others are there? How do they affect the body?

Answer: It is difficult to accurately count the different kinds of worms that infest humans because there are several ways of classifying these organisms. As an example, your term "stomach worm" could be applied to at least six different species of worms. Actually, I think it may be more meaningful to talk about the broader category of parasites instead of limiting my discussion to worms.

My American Heritage Dictionary defines a parasite as "an organism that grows, feeds, and is sheltered on or in a different organism while contributing nothing to the survival of its host." Certainly the worms you list fit this definition. However, the most common human parasite in the United States is not a worm but a protozoan, with the uncommon name Giardia lamdlia. This infestation is acquired by exposure to the bowel movement of an infected individual. This commonly occurs by drinking untreated water. Therefore, those drinking well water or drinking from those deceptively clear-appearing lakes and streams while hiking and camping are at greatest risk.

Most individuals with Giardia have foul-smelling diarrhea, abdominal distention, much flatulence, weight loss and a general fatigue. Similar symptoms are also common with parasites like roundworm, whipworm and hookworm, but in addition these, worms also produce anemia because of the amount of blood they suck from the host. Pinworm infestation, found more commonly in children in the United States than in those living in developing countries, usually causes only mild symptoms, including rectal itching.

Not all parasites are acquired from drinking contaminated water. Leishmaniasis is a potentially serious protozoan infestation transmitted by insect bites. This infestation causes fevers, skin sores, enlargement of the liver and spleen, weight loss, and weakness.

The parasite Stronglysides stercoralis is usually acquired by walking barefoot outdoors. The larvae of this parasite penetrate the skin of the foot and cause so little injury that the "parasitic invasion" properly called an "infestation" often goes unnoticed. The larvae are then carried by the bloodstream to the lungs, where they lodge and cause some irritation. This irritation produces coughing that brings up the larvae so that they are then swallowed and pass through the stomach and into the small intestine, where they mature into adults. The adult produces eggs that either mature into larvae that reenter the circulation to repeat the life cycle within the same person, or pass into the soil with the bowel movement. Those that pass into the soil can mature there and produce larvae that are capable of penetrating human skin. Complex, isn't it?  

Parasites are most common in warmer climates that make the complex life cycle of organisms like Stronglysides stercoralis easier to complete. Therefore, India, China, East and West Africa, Central and South America have more problems with parasitic infestations than Europe and North America. Proper sewage treatment and dependable, clean water for drinking, cooking and bathing also contribute significantly to reducing the frequency of illnesses caused by parasites.

Parasitic infestations are curable. Some are easily treated while others require strong medications with serious side effects. The greatest difficulty we physicians face in treatment of an individual with a parasite is making the correct diagnosis.

Unfortunately, most parasitic infestations begin with symptoms that mimic many other illnesses that are considerably more common in North America. Since parasitic infestations are uncommon, we doctors usually don't consider them until the tests for the more common illnesses are returned as negative. So, if you have been traveling outside the U.S. or think you may have a parasitic infestation, please say so to your doctor. It will remind her or him to look for the uncommon problems, too.

Family Medicine® is a weekly column. To submit questions, write to John C. Wolf, D.O., Ohio University College of Osteopathic Medicine, Grosvenor Hall, Athens, Ohio 45701.