Enterobius vermicularis, also called pinworm, is one of the most common nematode infections in the world. Originally, E. vermicularis was named Oxyuris vermicularis. Humans are the only natural host for this infection. Transmission occurs in people who are living in crowded environments and usually occurs within families. The worms are tiny, thread-like, and whitish. The worm is named after the characteristic pin-like tail present on the posterior part of female worms.
Infection most commonly occurs in children, but any individual is susceptible to E. vermicularis infection. People from tropical climates and school-aged children are the most vulnerable. Infection is caused by ingestion of the pinworm eggs. Route of infection is most commonly through the fecal-oral route.
The male to female infection frequency is 2 to 1. However, a female predominance of infection is seen in those between the ages of 5 and 14 years. It most commonly affects children younger than 18 years of age. It is also commonly seen in adults who take care of children, institutionalized children. Center for Disease Control and Prevention data indicates that there about 40 million people estimated to have been infected in the United States. Transmission can occur via contact with contaminated clothes, bedding, personal care products, and furniture. Fecal-oral is the most common mode of transmission. Rarely, transmission can occur via inhalation mode when eggs are inhaled and then subsequently swallowed.
Enterobius vermicularis is an organism that primarily lives in ileum and cecum. Once E. vermicularis eggs are ingested, they take about 1 to 2 months to develop into adult worms which happens in the small intestine. These do not usually cause any symptoms when confined to the ileocecal area. The female adult worms and ova migrate to the anal area mostly at night time and deposit thousands of eggs in the perianal area. This migration causes a lot of itching and pruritus. Eggs hatch near the anal area causing itching, scratching and this causes perianal pruritus. This leads to contamination of the fingers and results in ingestion of the eggs (autoinfection) and restarting of the life cycle of the worm. Occasionally, the larvae migrate back into the rectum and to the small intestine and begin the life cycle (retro infection).
Infection is usually benign, and about a third of the patients are asymptomatic. The most common symptoms associated with pinworm infestation is perianal itching. Perianal erythema may be seen due to the itching and scratching. Sometimes a superficial bacterial infection can occur at the scratching sites resulting in erythema and warmth. Persistent itching can cause disturbances in sleep and may lead to insomnia. Female genitourinary infections have also been reported in the literature. Water diarrhea has been reported in some patients. Sometimes abdominal pain and other serious complications like appendicitis can occur due to worms blocking the lumen in the appendix or lead to inflammation around the appendix. Sometimes tiny thread-like worms may be visible to the naked eye in the perianal area.
Enterobius can be diagnosed through a cellophane tape test or pinworm paddle test where an adhesive tape-like material is applied to the perianal area and then examined under a microscope. The examination might reveal characteristic ova which are 50 by 30 microns in size and have a flattened surface on one side or may reveal the worms. Female worms are around 8 to 13 mm long while male worms are 2 to 5 mm long. The examination is usually done early morning for higher diagnostic yield. If the examination is negative for five consecutive mornings, then the diagnosis is ruled out. Stool examination is not helpful in the diagnosis of E. vermicularis as they are only occasionally excreted in the stool usually. Sometimes analysis of the stool specimen is recommended to rule out other causes.
Treatment consists of the following antihelminthic medications:
Albendazole: Given on an empty stomach, a 400-mg, one-time dose followed by a repeat dose in 2 weeks
Mebendazole: A 100-mg, one-time dose followed by a repeat dose in two weeks
Pyrantel Pamoate: Available over the counter in the United States; Dose of 11 mg/kg up to a maximum 1 gm given 2 weeks apart
Other medications which have been used to treat enterobiasis are ivermectin and piperazine, although the latter has lower efficacy and higher toxicity.
Enterobiasis can cause recurrent reinfection, so treating the entire household, whether symptomatic or not is recommended to prevent recurrence.
Treatment of Enterobius infection in pregnancy should be reserved for patients who have significant symptoms. In pregnant patients, pyrantel pamoate is preferred over other medications.
Pyrantel pamoate can cause adverse effects like nausea, vomiting, anorexia, abdominal cramps, diarrhea. It should be avoided in children younger than 2 years of age. Mebendazole and albendazole should be avoided in the first trimester of pregnancy and children younger than 1 year of age. Pregnant patients should consult their doctors before initiating any therapy.
Prognosis following a pinworm infection is excellent. Patients are recommended to follow up with their physicians after completion of the treatment to make sure they do not have any reinfection. Is symptoms recur then testing and treatment as above should be re-initiated.
Occasionally a superficial bacterial infection can occur at the scratching sites due to intense perianal pruritus. Other complications reported are female genitourinary infections like vulvovaginitis, urinary tract infection in young girls. Appendicitis has also been reported as a consequence of longstanding pinworm infestation.
Patients should be educated on the need to maintain hygiene and wash their hands regularly to prevent the spread of infection and reinfection. Family members should recognize the signs and symptoms of pinworm infection early and should make sure that they get appropriate medications to treat it.
Preventive strategies recommended are:
Enterobius vermicularis infection is usually treated by the primary care physician or family physician. If having any difficulty in treating then the patient may be referred to specialists like an infectious disease or parasitologists. Pharmacists have a role in explaining to the patients the side effects of these medications used to treat pinworms as one of the drugs. Pyrantel pamoate is available over the counter in the United States. School nurses should also be aware of the manifestations of pinworm infection to prevent their spread in the schools and daycares.