Author: Roshni Nepal
Phylum – Nemathelminthes
Class – Nematoda
Genus – Enterobius
Species – Vermicularis
Pinworm infection is caused by a small, thin, white roundworm called Enterobius vermicularis. The nematode Enterobius vermicularis is widely known as the human pinworm due to the female’s long, pointed tail. Infection occurs by ingestion of eggs by 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.). 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 to start producing eggs.
Habitat and geographical distribution
The parasite resides in large intestine (caecum) and appendix in human host. They are found worldwide. Pinworms are particularly common in children. Because it spreads from host to host through contamination, enterobiasis is common among people living in close contact, and tends to occur in all people within a household.
Life cycle of E. vermicularis
Gravid adult female Enterobius vermicularis deposit eggs on perianal folds. Infection occurs via self-inoculation (autoinfection) (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 intestine and 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.
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.
Clinical manifestation of enterobiasis
Enterobiasis is frequently asymptomatic. The most typical symptom is perianal pruritus, especially at night, which may lead to 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.
Diagnosis of pinworm can be reached from three simple techniques. The first option is to look for the worms in the perianal region 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.
Treatment, prevention and control
- mebendazole, pyrantel pamoate, or albendazole.
- 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.
- 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; 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.