Know Your Parasites for the Physician Assistant Exam - dummies

Know Your Parasites for the Physician Assistant Exam

By Barry Schoenborn, Richard Snyder

For the Physician Assistant Exam (PANCE), you will need to know about malaria, pinworms, and helminths (flukes, tapeworms, roundworms, and the like). Recall that parasitism is a nonmutual relationship in which the parasite benefits at the expense of the host.


Someone contracts malaria after being bitten by an infected mosquito. These mosquitoes usually live in Asia, Africa, and South America and are carrying an infectious bug from the genus Plasmodium — technically, a eukaryotic protist.

When these little parasitic creatures get into the bloodstream, they can stay dormant in the liver for a while, and then they wreak havoc. They can affect multiple body systems, including the liver, blood cells, and kidney.

Signs and symptoms of malaria can include gastrointestinal upset, fever, icterus, hematochezia, myopathy, and even seizures. Labs can confirm the presence of a hemolytic anemia. You may see hepatosplenomegaly on physical examination or on imaging studies.

With malaria, you need to order a special malarial peripheral blood smear called a thick and thin blood smear. On this smear, you’re looking for the presence of parasites. This test can be repeated, and repeating the test is necessary if the initial smears are negative and you have a high clinical suspicion of malaria.

Medications such as chloroquine, the antibiotic doxycycline (Vibramycin), and atovaquone are frequently used together because of the high incidence of resistance to treatment. The atovaquone/proguanil combination (Malarone) can be used for malaria prophylaxis as well. If a patient is planning travel to areas where malaria is endemic, remind him or her to check the CDC’s travelers’ health website.

Make sure you know the type of malaria you’re dealing with. The Plasmodium genus contains 200 known species, and at least 11 of them love humans. The most common species are Plasmodium falciparum and Plasmodium vivax. Plasmodium falciparum is the most deadly, with the highest rate of fatalities compared to the other forms.


The most common pinworm is the Enterobius vermicularis. You can eliminate pinworms by eliminating them, but that doesn’t eliminate them. Is this a Buddhist kōan? Nope.

Pinworms are parasites that you acquire by eating them. The pinworm replicates in the gastrointestinal system. Then the pinworm lays its eggs in the anal region, where the person eliminates. From there, with the action of wiping or cleaning the anus, the eggs get on the hands and can spread to anything the person touches.

This usually happens with children, who may be careless about wiping — and washing — after a bowel movement. Diagnosis may be confirmed by visual inspection of the pinworms around the anus or a cellophane tape test in an attempt to identify the ovum or parasites.

The medication used to treat pinworms, albendazole (Albenza), eliminates them. It often needs to be administered for several months because there’s a high risk of reinfection, even when you’re treating this condition with medication. Hygiene, washing hands in particular, is very important in preventing reinfection. In addition, clothes should be washed frequently.


Helminths (parasitic worms) fall into four groups: monogeneans, cestodes (tapeworms), nematodes (roundworms), and trematodes (flukes). The trematodes include Necator americanus (hookworm) and parasites in the genus Schistosoma, which cause snail fever and other conditions.

Depending on the type of helminth you’re dealing with, symptoms can include liver failure, biliary problems, and intestinal issues. The tapeworm can cause malabsorption and other intestinal problems.

Only certain medications can be used to treat helminth infections. Examples are albendazole (Albenza) and mebendazole (Vermox).