eMedicine Specialties > Pediatrics: General Medicine > Parasitology

Enterobiasis

Author: Wayne Wolfram, MD, MPH, Clinical Associate Professor, Departments of Pediatrics, Children's Hospital and University of Cincinnati
Contributor Information and Disclosures

Updated: Nov 16, 2007

Introduction

Background

Enterobius vermicularis, a small nematode, is a common cause of helminthic infestation in the United States. The female nematode averages 10 mm X 0.7 mm, whereas males are smaller. All socioeconomic levels are affected, and infestation often occurs in family clusters. Infestation does not equate with poor home sanitary measures (an important point when discussing therapy).

Pathophysiology

E vermicularis is an obligate parasite; humans are the only natural host. Fecal-oral contamination via fomites (toys, clothes) is a common method of infestation. After ingestion, eggs usually hatch in the duodenum within 6 hours. Worms mature in as little as 2 weeks and have a life span of approximately 2 months.

Adult worms normally inhabit the terminal ileum, cecum, vermiform appendix, and proximal ascending colon. The worms live free in the intestinal lumen, and little evidence supports invasion of healthy tissue under normal conditions. The female worm migrates to the rectum after copulation and, if not expelled during defecation, migrates to the perineum (often at night), where an average of 11,000 eggs are released. Eggs become infectious within 6-8 hours and, under optimum conditions, remain infectious in the environment for as long as 3 weeks. Because of the short incubation time until the ova are infectious, eggs that are deposited under the fingernails during scratching and then placed in the mouth may be a mode of reinfection.

Frequency

United States

The prevalence is approximately 5-15% in the general population; however, this rate has declined in recent years. Prevalence rates are probably higher in institutionalized individuals. Humans are the only known host.

International

Prevalence data are not available, but E vermicularis infection is known to occur worldwide.

Mortality/Morbidity

• Secondary bacterial skin infection may develop from vigorous scratching to relieve pruritus.
• Reinfestation is common. Infection can develop as long as female pinworms continue to lay eggs on the skin.
• Restless sleeping often results from pruritus ani.

Race

All races are subject to infestation.

Sex

Infestation can occur in males and females.

Age

The prevalence is greatest in children aged 5-9 years, but all ages can be affected.

Clinical

History

• Patients are often asymptomatic. Worms may be incidentally discovered when worms are found in the perineal region.
• If patients are symptomatic, pruritus ani and pruritus vulvae are common presenting symptoms. However, one study failed to find an increase of these symptoms in infested children compared with matched control subjects.
• Restlessness during sleep is noted by the parents of many patients.

Physical

• Patients often have excoriation or erythema of the perineum, vulvae, or both, but infestation can occur without these signs.
• Visual sighting of a worm by a reliable source (eg, a parent) is usually accepted as evidence of infestation and grounds for treatment.
• Worms can be found in stools or on the patient's perineum before bathing in the morning.
• Occasionally, the gravid female worm may aberrantly migrate into the female genitalia and produce vaginitis. Incidental recovery at necropsy or surgery of small granulomatous lesions surrounding the worm, larvae, or eggs in the salpinx and peritoneum demonstrates the worm's ability to ascend the female genital tract.

Causes

• Enterobiasis is caused by the nematode E vermicularis.

• Search for CME/CE on This Topic »

• Nematode Infections (Infectious Diseases)
• Pinworms (Emergency Medicine)
• Pinworm (Infectious Diseases)