Enterobius Vermicularis - Pinworm

Human pinworm, Enterobius vermicularis, is the most common parasitic worm infection in the United States and Western Europe. Pinworms are easily transmitted from human to human and are particularly common in children. Luckily the disease, enterobiasis, causes only anal itching.

Enterobius vermicularis does not need an intermediate host to complete its life cycle. Humans get infected by accidentally swallowing or inhaling microscopic pinworm eggs. Once inside the first part of the small intestine, duodenum, pinworm larvae hatch from the eggs. The larvae are only about 0.15 mm long but grow very fast. They migrate towards the ending of the small intestine as they mature into adults. Adults are white, thin worms. Males are 0.2 mm thick and 2–5 mm long whereas females are 0.5 mm thick and 8–13 mm long. Life expectancy for males is seven weeks whereas females live 5–13 weeks. The males usually die after the pinworms have mated in the last part of the small intestine, ileum. The gravid (pregnant) female resides at the beginning of the large intestine, colon, eating what ever food passes through the intestinal tract. Female pinworm reaches fertility within four weeks. She swims at the rate of 12 cm per hour towards the rectum. During sleep when body temperature is low and there is less movement the female pushes out from the anus and lays eggs on the outside skin. The eggs get stuck on skin, underwear or bedding and become infective within a few hours. Eggs survive up to three weeks on clothing, sheets or other objects. After the female has laid 11000–16000 eggs it dies.

Sometimes pinworms lay eggs inside the colon. If the eggs are not taken out in the feces the larvae might have enough time to hatch. This can only happen in the large intestine or rectum and only if enough oxygen is present. The larvae migrate back up the intestinal tract and develop into adults. This is very rare but happens every now and then.

Diagnosis is made by identifying pinworms or their eggs. Worms can sometimes be seen on the skin around the anus 2–3 hours after falling asleep. Eggs can be collected using a transparent cellophane tape by pressing the sticky side of the tape to the anal skin. The eggs stick to the tape which can be placed on a slide and examined under a microscope by a doctor. Bathing or having a bowel movement can remove eggs from the skin. So this test should be done immediately after waking up. It needs to be repeated on the following two mornings to increase the chance of finding pinworm eggs.

Enterobiasis can be treated with either prescription or over-the-counter medications. A health care provider should be consulted before treating a suspected infection. Some common drugs against pinworms are albendazole and mebendazole. The drugs kill larvae and adults but not the eggs. To get rid of all pinworms another dose needs to be taken after two weeks to kill the newly hatched larvae. All family members should be treated at the same time. If children are in close contact with other children, like in kindergarten, then there is a possibility that other families are infected, too. The least embarrassing way to handle the situation is to only tell the kindergarten teacher. She will inform the other parents that their children might have pinworms and should be treated with the drug.

To prevent new infections always keep fingers out of your mouth and nose. Keep fingernails short and do not bite your nails. Wash your hands after using the toilet and before eating or preparing food. Change clothing, towels, and sheets frequently and wash them in hot water, especially during and after pinworm treatment. If you have pets, keep them clean. The human pinworm, Enterobius vermicularis, does not infect other animals but pets can carry eggs in their fur.

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Pinworm Quiz

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