Enterobiasis (Pinworm, Threadworm, Seatworm)

CHAPTER 69

Enterobiasis

(Pinworm, Threadworm, Seatworm)

Presentation

The patient complains of severe perianal and/or vaginal irritation and itching, which is worse at night and may contribute to insomnia or superinfection of the excoriated perianal skin. Children may exhibit only perianal pruritus and nocturnal restlessness. Rarely, more serious disease can result, including weight loss, urinary tract infection, and appendicitis. Often, an entire family is affected.

What To Do:

Examine the anus to rule out other causes of itching, such as rectal prolapse, fecal leakage, hemorrhoids, lice (pediculosis), fungal infections (tinea or candidiasis), or bacterial infections (erythrasma) (see discussion of pruritus ani on p 243).

Look for pinworms directly (especially if the patient comes in at night) and also by pressing the sticky side of cellophane tape wrapped around a tongue blade (sticky side up) to the perianal skin several times. Remove the tape and place it sticky side down on a glass slide. Examine the tape, under the low power of the microscope, for female worms (only 5% of infected persons have eggs in their stool) approximately 1 cm long, 0.5 mm in diameter, with pointed tails (Figure 69-1). Adult male pinworms are shorter (2.5 mm in length) and have a blunt tail. (Use shiny rather than “invisible” tape, because the latter’s rough surface makes microscopy difficult.) To increase this test’s sensitivity to approximately 90%, it should be conducted right after the patient awakens on at least 3 consecutive days.

Figure 69-1 Pinworm examples.

If you see pinworms or still suspect them, administer one oral dose of pyrantel pamoate, 11 mg/kg (maximum l g), to all family members. This can be obtained over the counter as Pin-X, Pin-Rid, and Reese’s Pinworm Medicine (oral suspension 250 mg/5 mL). This should be repeated in 2 weeks. This treatment has lower efficacy and greater side effects (vomiting, diarrhea, anorexia, and nausea) than the medications available by prescription.

Two prescription medications are mebendazole (Vermox), 100-mg chewable tablet once PO (not for children younger than 2 years of age), and albendazole (Albenza), 400 mg in adults or 10 mg/kg in children as a single dose. Both of these prescription medications should be repeated after 2 weeks. All three of these medications are considered unsafe during pregnancy.

Explain to all concerned that this is not a dangerous infection and should be eradicated from the whole family after one or two treatments. Have the family clean their bedrooms and bedding. Explain that thorough hand washing is important, because pinworms are transmitted by direct anus to mouth spread, by direct contact with dirty linens or clothing, or by dirty hands contaminating food during its preparation or consumption.

Discussion

There is evidence of pinworm infection that dates back to Roman-occupied Egypt (30 BC to AD 395). Enterobius vermicularis is also the oldest and most common parasite for which we have direct evidence in the New World, with fecal samples positive for pinworm ova from the American Southwest dating back 10,000 years. The pinworm, threadworm, or seatworm is a nematode, or roundworm, with the largest geographic range of any helminth. It is the most prevalent nematode in the United States. Humans are the only known host, and perhaps 10% of the U.S. population may harbor pinworms, especially children.

Adult worms are quite small; the males range in size from 2 to 5 mm, and the females measure 8 to 13 mm (Figure 69-2). The worms live primarily in the cecum of the large intestine, from which the gravid female migrates at night to lay up to 15,000 eggs on the perineum. The eggs can be spread by the fecal-oral route to the original host and new hosts. In this manner, an entire family can become infected. Ingested eggs hatch in the duodenum, and larvae mature during their migration to the large intestine.

Figure 69-2 A, Numerous pinworms scattered throughout the colon as seen with colonoscopy. B, The adult female worm with a long, pointed tail. C, The adult male pinworm is short with a blunt tail. (Adapted from Faruqi S, Ahmed I, Membreno F: Pinworms. Gastrointest Endosc 57:566, 2003.)

Fortunately, most eggs desiccate and die within 72 hours. In the absence of host autoinfection, infestation usually lasts only 4 to 6 weeks. Egg deposition causes perineal, perianal, and vaginal irritation. The patient’s constant itching in an attempt to relieve irritation can lead to potentially debilitating sleep disturbance.

Direct visualization of the white-appearing adult worms or microscopic detection of worms or eggs using the “cellophane tape test” confirms the diagnosis.

Pruritus ani has many causes, of which pinworm is just one. Consider diet (coffee, tea, chocolate, citrus), malignancy, anal fistulas, other infections (yeast, sexually transmitted diseases [STDs], Corynebacterium), psoriasis, Paget disease, or even incomplete cleansing postdefecation as you evaluate the patient with this complaint.