Updated: Apr 27, 2016
  • Author: Wayne Wolfram, MD, MPH; Chief Editor: Russell W Steele, MD  more...
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Enterobius vermicularis is a small nematode This common helminthic infestation has an estimated prevalence of 40 million infected individuals in the United States. [1] The female nematode averages 10 mm X 0.7 mm, whereas males are smaller. All socioeconomic levels are affected. Infestation often occurs in family clusters. Infestation does not equate with poor home sanitary measures (an important point when discussing therapy).



E vermicularis is an obligate parasite; humans are the only natural host. Fecal-oral contamination via hand-mouth contact or via fomites (toys, clothes) are common methods 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. 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.

See the image below.

Because of the short incubation time until the ova 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 reinfestation.



United States

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.

Infestation rate increases with increased population density, and with personal habits such as thumb sucking


E vermicularis infestation occurs worldwide. Prevalence data vary by country.

A study that aimed to determine the extent of enterobiasis, strongyloidiasis, and other helminth infections in infants, preschool-aged, and school-aged children from rural coastal Tanzania reported that enterobius vermicularis infections were found in 4.2% of infants, 16.7%, of preschool-aged children, and 26.3% of school-aged children. [2]

Infestation rates increase with increased population density and with certain personal habits like thumb-sucking. [3, 4]


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 may be due to pruritus ani. Infestation has been reported to cause enuresis.


Although other helminthic infection rates are shown to be higher in patients with HIV, studies to date have not shown a statistically significant difference for Evermicularis. [5]


All races are subject to infestation.


Infestation can occur in males and females.


The people most likely to be infected with pinworms are children younger than 18 years, people who take care of infected children, and people who are institutionalized. In these groups, the prevalence can reach 50%. [6] However, individuals can be affected regardless of age or health status.