Parasites are organisms which depend on other organisms for nutrition to live. Most parasites are in the form of worms and flukes known as Helminths. These organisms are acquired by the hosts from the food that they eat, water and soil. Parasitism is most common in children but can also happen in adults. Some parasites derive benefit without causing injury to the host. This is called Commensalism type of parasitism. There is also a type of parasitism wherein the two organisms cannot exist independently. This is called Symbiosis. The Mutualism type is wherein the two organisms are both beneficial to each other.
Enterobius vermicularis, commonly known as the pinworm or the seatworm, is the most common cause of parasitism in children in the United States. Pinworms have the broadest geographic range of any helminth, and are the most prevalent helminth infection in the USA and Western Europe. It is commonly found in school-aged children, though it is seen in adults as well. The worms are small, white, and threadlike, with the larger females ranging between 8-13 mm x 0.3-0.5 mm and the smaller males ranging between 2-5 mm x 0.1-0.2 mm. Females also possess a long, pin-shaped posterior end from which the parasite's name is derived. They dwell primarily in the cecum of the large intestine, from where the gravid females migrate at night to lay up to 15,000 eggs on the perineum. Pinworm eggs are flattened asymmetrically on one side, ovoid, approximately 55 mm x 25 mm in size and embryonate in six hours. It has been speculated recently that Enterobius vermicularis also plays as an intermediate host for another helminth which is Diantamoeba fragilis. Parasitism of this organism is manifested by nocturnal anal pruritus or itchiness. Skin abscess can result due to excessive scratching of the perianal skin. Adult pinworms dwell in the cecum and appendix disrupting proper absorption which is manifested by malnutrition.
Humans acquire infection through the ingestion of eggs which hatch in the small intestine and become larvae. The larvae develop to adults separately as males and females in the colon and mate. Fertilized females migrate to the anus at night to release eggs at the perianal skin. These eggs hatch into infective larvae 6 hours after.
The most common manifestation of pinworm parasitism is the nocturnal anal pruritus or night time anal itching. This is caused by the migration of female pinworms to the anus to lay eggs, specifically, insertion of the tail pin into the mucosa for ovideposition, and scratching leads to finger contamination and subsequently the spread of ovum to others. The scratching may also excoriate the skin and lead to secondary bacterial infections. Secondary symptoms, which are due to disturbed sleep caused by pruritis, include anorexia and irritability. However, pinworm infection is not always harmless, as it has been implicated in causing appendicitis, as high as 2.39% of cases in developing countries, intestinal obstruction, intestinal perforation, enterocolitis mimicking Crohn's disease, and eosinophilic ileocolitis.
The most commonly used technique of collecting eggs of pinworms for sample and diagnostics is the Cellophane technique. This must be done early morning. A Scotch tape is mounted to the perianal skin; the tape will then be examined by microscopy for the presence of D-shaped ova that stick in the tape. These eggs may also be stained blue with lactophenol cotton blue, which aids in detection and identification. The sensitivity of this test when performed for three consecutive mornings is 90%. Anal swabs or 'Swube tubes" may also be used. Extra-intestinal infections may require more invasive diagnostic tests. One case diagnosed via colonscopy followed by confirmation via microscopy and infections of the female genital tract usually require laparotomy and excision of granulomas for a conclusive diagnosis. Pre-operative diagnosis of finding the parasite via cervical smears, vaginal wet mounts, and vaginal pooled specimen is possible but difficult. Alternatively, the adults may be seen in stool or toilet paper, though the ova and larvae are rarely present in either the stool or urine.
The drugs recommended in eliminating Enterobius vermicularis are the Antihelminthics such as Mebendazole and Pyrantel pamoate. Antihelminthics are usually taken orally, in a quantity appropriate to the child's weight, given once a day at bedtime as a single dose.
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