Pinworm

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The pinworm (Genus Enterobius), also known as threadworm or seat worm, is a common human intestinal parasite, especially in children.^[5] The medical condition associated with pinworm infestation is known as enterobiasis^[6] , or sometimes oxyuriasis.^[7]

[edit] Classification

The pinworm is a a type of roundworm, and two species of pinworm have been identified with certainty.^[8] Humans are host only to Enterobius vermicularis (formerly Oxyuris vermicularis).^[9] Chimpanzees are host to Enterobius anthropopitheci, which is morphologically distinguishable from the human pinworm.^[3] There is also a claim for another species affecting humans, Enterobius gregorii, which is supposedly a sister species of E. vermicularis, and has a slightly smaller spicule.^[10] Its existence is controversial however, as some consider there to be insufficient evidence^[4], and others contend that E. gregorii is a younger stage of E. vermicularis.^[2][3] Regardless of its status as a distinct species, E. gregorii is considered clinically identical to E. vermicularis.^[9]

[edit] Morphology

Enterobius vermicularis egg under a light microscope.

The adult pinworm male is 1–4 mm in length, while the adult female is 8–13 mm and possesses the long, pin-shaped posterior for which the worm is named.

[edit] Habitat

The pinworm lives in the large intestine and cecum. It is found worldwide, and causes the most common infection enterobiasis in humans. Unlike many other intestinal parasites, the pinworm does not usually enter the bloodstream or any other organs besides the intestines. Only in rare cases are pinworms found in the vagina, and even more rarely in the uterus, fallopian tubes, liver, and peritoneum, but the worms cannot survive long in these places.

The human pinworm Enterobius vermicularis is a ubiquitous parasite of man, it being estimated that over 200 million people are infected annually. It is more common in the temperate regions of Western Europe and North America (its existence is relatively rare in the tropics), and is found particularly in children. Samples of Caucasian children in the U.S.A. and Canada have shown incidences of infection of between 30% to 80%, with similar levels in Europe.^[11] Children are more likely than adults to acquire the infestation because they are more likely to play with soil and mud and insert their fingers in their mouths without washing them first.

[edit] Reproduction

Pinworm eggs are easily seen under a microscope.

Pinworms mate by traumatic insemination. After mating, the male dies. The female migrates to the anus and emerges, usually during the night, to deposit about 10,000 to 20,000 eggs in the perianal area (around the anus). She then secretes a substance which causes a very strong itching sensation, inciting the host to scratch the area and thus transfer some of the eggs to the fingers. Eggs can also be transferred to cloth, toys, and the bathtub. Once ingested orally, the larvae hatch in the small intestine, specifically the duodenum, and migrate back to the large intestine where they mature. Maturity is reached in 30–45 days. The eggs can survive for 2 to 3 weeks on their own outside of the human body. In some cases, the larvae will hatch in the peri-anal area and travel back inside the anus, up the rectum, and back into the intestines where they mature.^[12]

[edit] Effects

Except for itching, pinworm infestation does not usually cause any direct damage to the body. However, the unsanitary scratching of the itch can spread germs from the fingers to other parts of the body. This scratching occurs even as the person is asleep and can easily contribute to unhealthy skin conditions or infections. Sleep disturbance may arise from the itching or crawling sensations. Some case reports suggest that severe infestation may be associated with an increased risk for appendicitis. There is also some evidence of an association between enterobiasis and diminished zinc levels.^{[citation needed]}

[edit] Diagnosis

Pinworms are sometimes diagnosed incidentally by pathology. Micrograph of male pinworm in cross-section. Alae (blue arrow), intestine (red arrow) and testis (black arrow). H&E stain.

Diagnosis is often made clinically by observing the female worm (or many worms) in the peri-anal region, but can also be made using the "scotch-tape" test, in which the sticky side of a strip of cellophane tape is pressed against the peri-anal skin, then examined under a microscope for pinworm eggs.

Self-diagnosis is also possible without observing worms around the anus. Crawling sensations inside the anus indicate female pinworm migration, and they may be visually detected at this time by using lubricant to insert a finger into the anus, hooking it slightly, and pulling the finger out while at the same time gently scraping the rectal wall.^{[citation needed]} This may cause some of the thread-like pinworms to adhere to the lubricated finger, and they may thus be extracted from the anus. The method reqiures a sufficient number of repetitions, and scraping of all sides of the rectal wall. The method can also be used to provide temporary relief from intense crawling sensations caused large numbers of pinworms in the lower rectal area, simply by manually removing some of them.^{[citation needed]}

The pinworms may be seen in the host's faeces; however the eggs are invisible to the naked eye.

The diagnostic characteristics are: size 50-60 µm by 20-32 µm; typical elongated shape, with one convex side and one flattened side and colorless shell ^[13].

On histologic cross-section, alae or wings (running the length of the worm) are identifying features of the pinworm (see micrograph).^[14]

[edit] Treatment

Anti-pinworm drugs such as albendazole (Albenza), mebendazole (Vermox, OVEX), Piperazine and pyrantel pamoate (Pin-X, Reese's Pinworm Medication) are commonly used to treat pinworms as well as ascaris lumbricoides (the roundworm). It is not a necessity to visit a doctor to get these drugs, as pyrantel pamoate (Pin-X) is available as an over-the-counter medication (albendazole and mebendazole are prescription in the US); ask a pharmacist for medicines to treat pinworms (or threadworms as they are known in the UK). These medicines kill the pinworms 95% of the time, but do not kill the eggs. The person being treated should receive a second course after two weeks. Another precaution is to wash the hands before eating with special emphasis given to the area under the nails (to prevent any pinworm eggs under the fingernails from being ingested) and to wash any area or clothes which have touched or been in the vicinity of the infected areas. Treating the entire family concurrently is often necessary for cure, as the worms are easily passed back and forth between members of the household^[15] Leafy green vegetables (lettuce, spinach, cabbage etc) eaten raw are sometimes implicated in pinworm infestation. Since they are difficult to wash thoroughly, it is recommended that they be picked apart, leaf by leaf, and submerged in a water and vinegar solution for several minutes before rinsing and serving.

[edit] Additional images

Two pinworms, captured on emergence from the anus. Markings are 1 mm apart.

Pinworms are sometimes diagnosed incidentally by pathology. Micrograph of pinworms in the appendix. H&E stain.

High magnification micrograph of a pinworm in cross-section in the appendix. H&E stain.

High magnification micrograph of a pinworm in cross-section in the appendix. H&E stain.

[edit] See also

• List of parasites (human)

[edit] References

[edit] External links

• New England Journal of Medicine Video of infected colon
• NHS Direct Health encyclopaedia - Threadworms
• Experiences about Threadworm (Patient UK forum)
• Pinworm facts, life cycle, references at MetaPathogen