Surprising finding on colonoscopy
While looking for the cause of our patient’s intermittent rectal bleeding, we discovered something else entirely.
Diagnosis: Enterobiasis
The colonoscopy and aspiration results revealed Enterobius vermicularis, or pinworm infection. E vermicularis is the most common intestinal parasite seen by primary care physicians in North America and has a wide geographic distribution.1 In the United States, more than 40 million people are estimated to be infected with pinworm, and up to 30% are children.2 Adult worms are not commonly found on colonoscopy, in part because endoscopists are not anticipating them.3
Upon further questioning after the colonoscopy, our patient reported having “worms” as a child and being treated for them. He denied recent symptoms of perianal itching. He also denied a recent history of contact with children.
Infection is via the fecal-oral route
The life cycle of E vermicularis consists of egg, larvae, and adult worm stages. Infection occurs by the fecal-oral route, with hosts including humans and cockroaches.4
The adult pinworm is very small (females average 10 mm in length; males are 4 mm in length) with a lifespan of 1 to 2 months. Infection begins with ingestion of ova, which hatch in the duodenum. The larvae mature into adult worms as they migrate through the small intestine. The adult worms then reside in the cecum, and occasionally the appendix.
The gravid female worms migrate to the perianal region at night to deposit their eggs, laying about 15,000 eggs at once. This leads to perianal itching. Reinfection occurs by hand-to-mouth transmission of the eggs from perianal scratching.1-3
Differential Dx: Roundworms, whipworms, and threadworms
Other common parasitic helminthes in the United States include Ascaris lumbricoides (roundworm) and Trichuris trichiura (whipworm). Strongyloides stercoralis (thread worm) and Necator americanus and Ancylostoma duodenale (hookworms) are less common here but should be considered in immigrants, such as our patient. Tapeworms are another parasitic helminth, but tend to be flat in appearance, unlike the worms in this case.
Roundworms are the largest of the parasitic helminthes listed here, and are common in the southeastern states’ rural population. Larvae penetrate the intestine, enter the lymphatics, and travel to the lungs. Here they may cause Loffler’s pneumonia, which is usually self-limited (lasting 1-2 weeks) and often goes undiagnosed. Juvenile worms are coughed up and swallowed, returning to the small intestine, where they mature and survive for 12 to 18 months.1
