Pinworm (parasite)

The pinworm (genus Enterobius) is a type of roundworm (nematode), and three species of pinworm have been identified with certainty. Humans are hosts only to Enterobius vermicularis (formerly Oxyurias vermicularis). Chimpanzees are host to Enterobius anthropopitheci, which is morphologically distinguishable from the human pinworm. Hugot (1983) claims another species affects humans, Enterobius gregorii, which is supposedly a sister species of E. vermicularis, and has a slightly smaller spicule (i.e., sexual organ). Its existence is controversial, however; Totkova et al. (2003) consider the evidence to be insufficient, and Hasegawa et al. (2006) contend that E. gregorii is a younger stage of E. vermicularis. Regardless of its status as a distinct species, E. gregorii is considered clinically identical to E. vermicularis. == Morphology ==

The adult female has a sharply pointed posterior end, is 8 to 13 mm long, and 0.5 mm thick. The adult male is considerably smaller, measuring 2 to 5 mm long and 0.2 mm thick, and has a curved posterior end. Image:Pinworms in the Appendix (1).jpg|Pinworms are sometimes diagnosed incidentally by pathology. Micrograph of pinworms in the appendix, H&E stain Image:Pinworms in the Appendix (3).jpg|High magnification micrograph of a pinworm in cross section in the appendix, H&E stain File:Enterobius vermicularis - intermediate magnification.jpg|Partially longitudinal cross-section of Enterobius vermicularis, H&E stain File:Enterobius vermicularis egg.jpg|Cross-section of early E. vermicularis egg, H&E stain File:Histopathology of enterobius vermicularis eggs, HE stain.jpg|Later E. vermicularis eggs, of the same size as early eggs but having undergone more mitoses. H&E stain Image:Evermicularis worm4 HB.jpg|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 Image:Enterobius vermicularis (01).tif|Pinworm eggs are easily seen under a microscope. Image:Head of Enterobius vermicularis human pinworm 5230 lores.jpg|This micrograph reveals the cephalic alae in the head region of E. vermicularis. Image:Enterobius vermicularis-1.jpg|E. vermicularis ==Life cycle==

The entire life cycle, from egg to adult, takes place in the human gastrointestinal tract of a single host, or about 4–8 weeks. Although infection often occurs via ingestion of embryonated eggs by inadequate hand washing or nail biting, inhalation followed by swallowing of airborne eggs may occur rarely. and are passed out with stool. The gravid female pinworms settle in the ileum, caecum (i.e., beginning of the large intestine), appendix and ascending colon, where they attach themselves to the mucosa and ingest colonic contents. Almost the entire body of a gravid female becomes filled with eggs. The estimations of the number of eggs in a gravid female pinworm range from about 11,000 to 16,000. The egg-laying process begins about five weeks after initial ingestion of pinworm eggs by the human host. The gravid female pinworms migrate through the colon towards the rectum at a rate of 12 to 14 cm per hour. They emerge from the anus, and while moving on the skin near the anus, the female pinworms deposit eggs either through (1) contracting and expelling the eggs, (2) dying and then disintegrating, or (3) bodily rupture due to the host scratching the worm. After depositing the eggs, the female becomes opaque and dies. The female emerges from the anus to obtain the oxygen necessary for the maturation of the eggs. ==Infection==

E. vermicularis causes the medical condition pinworm infection also known as enterobiasis, whose primary symptom is itching in the anal area. Extraintestinal disease is rare and most commonly involves the female reproductive tract, but spleen abscess has also been reported. In conditions of rural poverty, Enterobius vermicularis infections are reported to be correlated with stunting and lower mean I.Q. among prepubescent children. == Diagnosis and treatment ==

A parasitic pinworm infection can be diagnosed by examining the anal area for visible eggs or worms, ideally at night due to the nocturnal nature of E. vermicularis. Another common at-home test is referred to as the “tape test”, during which tape is applied to the skin around the anus, preferably in the morning before showering or using the toilet. If any eggs are present, they will stick to the tape, which can then be taken to be examined by a medical professional. Once diagnosed, pinworm infections can be treated with an anti-parasite medication that will kill the worms. The medications that are most commonly prescribed for pinworms are albendazole and mebendazole. Initially, a single dose will be given, then followed by a repeat dose two weeks later in order to eliminate any newly-hatched worms that may be present. ==Distribution==

The pinworm has a worldwide distribution, and is the cause of the most common helminthiasis (parasitic worm infection) in the United States, western Europe, and Oceania. In the United States, a study by the Center of Disease Control reported an overall incidence rate of 11.4% among children. Because it spreads from host to host through contamination, pinworms are common among people living in close contact, and tends to occur in all people within a household. showing that parasitic pinworms already infested pre-mammalian cynodonts. The earliest known instance of the pinworms associated with humans is evidenced by pinworm eggs found in human coprolites carbon dated to 7837 BC found in western Utah. ==See also==