Enterobiasis

Enterobiasis is infestation by a pinworm

Enterobius tip

Pinworms

Pinworm infection is caused by a small, thin, white roundworm called Enterobius vermicularis. Although pinworom infection can affect all people, it most commonly occurs among children, institutionalized persons, and household members of persons with pinworm infection. Pinworm infection is treatable with over-the-counter or prescription medication, but reinfection, which occurs easily, should be prevented.

Risk Factors

The people most likely to be infected with pinworm are children under 18, people who take care of infected children and people who are institutionalized. In these groups, the prevalence can reach 50%.

Enterobius vermicularis Life Cycle

Pinworm is the most common worm infection in the United States. Humans are the only species that can transfer this parasite. Household pets like dogs and cats cannot become infected with human pinworms. Pinworm eggs can survive in the indoor environment for 2 to 3 weeks.

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Evermicularis egg UVa

Epidemiology

Pinworm infections are more common within families with school-aged children, in primary caregivers of infected children, and in institutionalized children.

A person is infected with pinworms by ingesting pinworm eggs either directly or indirectly. These eggs are deposited around the anus by the worm and can be carried to common surfaces such as hands, toys, bedding, clothing, and toilet seats. By putting anyone’s contaminated hands (including one’s own) around the mouth area or putting one’s mouth on common contaminated surfaces, a person can ingest pinworm eggs and become infected with the pinworm parasite. Since pinworm eggs are so small, it is possible to ingest them while breathing. Once someone has ingested pinworm eggs, there is an incubation period of 1 to 2 months or longer for the adult gravid female to mature in the small intestine. Once mature, the adult female worm migrates to the colon and lays eggs around the anus at night, when many of their hosts are asleep. People who are infected with pinworm can transfer the parasite to others for as long as there is a female pinworm depositing eggs on the perianal skin. A person can also re-infect themselves, or be re-infected by eggs from another person.

Causal Agent

The nematode (roundworm) Enterobius vermicularis is widely known as the human pinworm due to the female’s long, pointed tail. In some areas the common names “seatworm” and “threadworm” are used (the latter of which is sometimes also used to refer to Strongyloides stercoralis). Another putative pinworm species, Enterobius gregorii, has been described and reported from humans in Europe, Africa, and Asia. However, further morphologic and molecular evidence suggests E. gregorii likely represents an immature form of E. vermicularis. The rat pinworm, Syphacia obvelata, has also very rarely been reported infecting humans.

E vermicularis eggs

lifecycle

Gravid adult female Enterobius vermicularis deposit eggs on perianal folds. Infection occurs via self-inoculation (transferring eggs to the mouth with hands that have scratched the perianal area) or through exposure to eggs in the environment (e.g. contaminated surfaces, clothes, bed linens, etc.). Following ingestion of infective eggs, the larvae hatch in the small intestineand the adults establish themselves in the colon, usually in the cecum. The time interval from ingestion of infective eggs to oviposition by the adult females is about one month. At full maturity adult females measure 8 to 13 mm, and adult males 2 to 5 mm; the adult life span is about two months. Gravid females migrate nocturnally outside the anus and oviposit while crawling on the skin of the perianal area. The larvae contained inside the eggs develop (the eggs become infective) in 4 to 6 hours under optimal conditions.

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Pinworms (Enterobiasis) in the Lumen of the Vermiform Appendix

Rarely, eggs may become airborne and be inhaled and swallowed. Retroinfection, or the migration of newly hatched larvae from the anal skin back into the rectum, may occur but the frequency with which this happens is unknown.

Hosts

Oxyurid nematodes (pinworms) generally exhibit high host specificity. Humans are considered the only host for E. vermicularis, although occasional infections have been reported in captive chimpanzees.

Geographic Distribution

E. vermicularis occurs worldwide, with infections occurring most frequently in school- or preschool-children and in crowded conditions.

Clinical Presentation

Enterobiasis is frequently asymptomatic. The most typical symptom is perianal pruritus, especially at night, which may lead to excoriations and bacterial superinfection. Occasionally, invasion of the female genital tract with vulvovaginitis and pelvic or peritoneal granulomas can occur. Other symptoms include, teeth grinding, enuresia, insomnia, anorexia, irritability, and abdominal pain, which can mimic appendicitis. E. vermicularis larvae are often found within the appendix on appendectomy, but the role of this nematode in appendicitis remains controversial. Very rare instances of eosinophilic colitis associated with E. vermicularis larvae have been reported.

Disease

The most common clinical manifestation of a pinworm infection is an itchy anal region. When the infection is heavy, there can be a secondary bacterial infection due to the irritation and scratching of the anal area. Often the patient will complain of teeth grinding, and insomnia due to disturbed sleep, or even abdominal pain or appendicitis. Infection of the female genital tract has been well reported.

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Evermicularis egg

Diagnosis

A person infected with pinworm is often asymptomatic, but itching around the anus is a common symptom. Diagnosis of pinworm can be reached from three simple techniques. The first option is to look for the worms in the perianal reqion 2 to 3 hours after the infected person is asleep. The second option is to touch the perianal skin with transparent tape to collect possible pinworm eggs around the anus first thing in the morning. If a person is infected, the eggs on the tape will be visible under a microscope. The tape method should be conducted on 3 consecutive mornings right after the infected person wakes up and before he/she does any washing. Since anal itching is a common symptom of pinworm, the third option for diagnosis is analyzing samples from under fingernails under a microscope. An infected person who has scratched the anal area may have picked up some pinworm eggs under the nails that could be used for diagnosis.

Since pinworm eggs and worms are often sparse in stool, examining stool samples is not recommended. Serologic tests are not available for diagnosing pinworm infections.

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Cross-section of a male Enterobius vermicularis from tissue,

Treatment

The medications used for the treatment of pinworm are either mebendazole, pyrantel pamoate, or albendazole. Any of these drugs are given in one dose initially, and then another single dose of the same drug two weeks later. Pyrantel pamoate is available without prescription. The medication does not reliably kill pinworm eggs. Therefore, the second dose is to prevent re-infection by adult worms that hatch from any eggs not killed by the first treatment. Health practitioners and parents should weigh the health risks and benefits of these drugs for patients under 2 years of age.

Repeated infections should be treated by the same method as the first infection. In households where more than one member is infected or where repeated, symptomatic infections occur, it is recommended that all household members be treated at the same time. In institutions, mass and simultaneous treatment, repeated in 2 weeks, can be effective.

Prevention & Control

Washing your hands with soap and warm water after using the toilet, changing diapers, and before handling food is the most successful way to prevent pinworm infection. In order to stop the spread of pinworm and possible re-infection, people who are infected should bathe every morning to help remove a large amount of the eggs on the skin. Showering is a better method than taking a bath, because showering avoids potentially contaminating the bath water with pinworm eggs. Infected people should not co-bathe with others during their time of infection.

Also, infected people should comply with good hygiene practices such as washing their hands with soap and warm water after using the toilet, changing diapers, and before handling food. They should also cut fingernails regularly, and avoid biting the nails and scratching around the anus. Frequent changing of underclothes and bed linens first thing in the morning is a great way to prevent possible transmission of eggs in the environment and risk of reinfection. These items should not be shaken and carefully placed into a washer and laundered in hot water followed by a hot dryer to kill any eggs that may be there.

In institutions, day care centers, and schools, control of pinworm can be difficult, but mass drug administration during an outbreak can be successful. Teach children the importance of washing hands to prevent infection.

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