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Enterobiasis

Pinworm infection
Classification and external resources
File:Evermicularis.jpg
Pinworms (Enterobius vermicularis).
ICD-10 B80.
ICD-9 127.4
DiseasesDB 13041
MeSH D017229

A pinworm infection or enterobiasis is the infestation with enterobius (pinworms)[1] or less precisely as oxyuriasis in reference to the family oxyuridae.[2].

The incubation time from ingestion of eggs to the first appearance of new eggs around the anus is 4 to 6 weeks.[3]. The primary symptoms are itching around the anus mainly at night due to the presence of the small worms. Mebendazole is an effective and safe treatment.

Contents

Signs and symptoms

One third of individuals with pinworm infection are totally asymptomatic.[3] The main symptoms are pruritus ani and perineal pruritus, i.e., itching in and around the anus and around the perineum.[4][5][3] The itching occurs mainly during the night,[4][6] and is caused by the female pinworms migrating to lay eggs around the anus.[7][5] Both the migrating females and the clumps of eggs are irritating, but the mechanisms causing the intense pruritus have not been explained.[6] The intensity of the itching varies, and it can be described as tickling, crawling sensations, or even acute pain.[8] The itching leads to continuously scratching the area around the anus, which further results in tearing of the skin and complications such as secondary bacterial infections, including bacterial dermatitis (i.e., skin inflammation) and folliculitis (i.e., hair follicle inflammation).[5][4][8] General symptoms are insomnia (i.e., persistent difficulties to sleep) and restlessness.[4] A considerable proportion of children suffer from anorexia (i.e., loss of appetite), weightloss, irritability, emotional instability, and enuresis (i.e., inability to control urination).[4]

Pinworms cannot damage the skin,[9] and they do not normally migrate through tissues.[5] However, in women they may move onto the vulva and into the vagina, from there moving to external orifice of the uterus, and onwards to the uterine cavity, fallopian tubes, ovaries, and peritoneal cavity.[9] This can cause vulvovaginitis, i.e. an inflammation of the vulva and vagina.[5][4] This causes vaginal discharge and pruritus vulvae, i.e., itchiness of the vulva.[4] The pinworms can also enter the urethra, and presumably, they carry intestinal bacteria with them.[9] According to Gutierrez (2000), a statistically significant correlation between pinworm infection and urinary tract infections has been shown,[9] however Burkhart & Burkhart (2005) maintain that the incidence of pinworms as a cause of urinary tract infections remains unknown[3] Incidentally, one report indicated that 36% of young girls with urinary tract infection also had pinworms.[3] Dysuria (i.e., painful urination) has been associated with pinworm infection.[3]

The relationship between pinworm infestation and appendicitis has been researched, but there is a lack of clear consensus in the matter: while Gutierres (2005) maintains that there exists a consensus that pinworms do not produce the inflammatory reaction,[10] Cook (1994) states that it is controversial whether pinworms are causatively related to acute appendicitis,[8] and Burkhart & Burkhart (2004) state that pinworm infection causes symptoms of appendicitis to surface.[3]

Cause

The cause of a pinworm infection is the worm enterobus. The entire lifecycle — from egg to adult — takes place in the human gastrointestinal tract of a single human host.[7][11] Cook et. al (2009) and Burkhart & Burkhart (2005) disagree over the length of this process, with Cook et. al stating two to four weeks,[4] while Burkhart & Burkhart states that it takes from four to eight weeks.[12]

The lifecycle begins with eggs being ingested.[7]. The eggs hatch in the duodenum (i.e., first part of the small intestine).[13] The emerging pinworm larvae grow rapidly to a size of 140 to 150 micrometers in size,[4] and migrate through the small intestine towards the colon.[7] During this migration they moult twice and become adults.[7][12] Females survive for 5 to 13 weeks, and males about 7 weeks.[7] The male and female pinworms mate in the ileum (i.e., last part of the small intestine),[7] whereafter the male pinworms usually die,[13] and are passed out with stool.[6] The gravid female pinworms settle in the ileum, caecum (i.e., beginning of the large intestine), appendix and ascending colon,[7] where they attach themselves to the mucosa[12] and ingest colonic contents.[5] Almost the entire body of a gravid female becomes filled with eggs.[13] The estimations of the number of eggs in a gravid female pinworm ranges from about 11,000[7] to 16,000[12]. The egg-laying process begins approximately five weeks after initial ingestion of pinworm eggs by the human host.[7] The gravid female pinworms migrate through the colon towards the rectum at a rate of 12 to 14 centimeters per hour.[7] 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.[13] After depositing the eggs, the female becomes opaque and dies.[6] The reason the female emerges from the anus is to obtain the oxygen necessary for the maturation of the eggs.[6]

Diagnosis

File:Pinworms in the Appendix (2).jpg
High magnification micrograph of a pinworm in cross section in the appendix. H&E stain.

Diagnosis depends on finding the eggs or the adult pinworms.[13] Individual eggs are invisible to the naked eye, but they can be seen using a low-power microscope.[14] On the other hand, the light-yellowish thread-like adult pinworms are clearly visually detectable, usually during the night when they move near the anus, or on toilet paper.[14][8][3]. Transparent adhesive tape (e.g. Scotch Tape) applied on the anal area will pick up deposited eggs, and diagnosis can be made by examining the tape with a microscope.[10][14] This test is most successful if done every morning for several days, because the females do not lay eggs every day, and the number of eggs vary.[14]

Pinworms do not lay eggs in the feces,[14] but sometimes eggs are deposited in the intestine.[13] As such, routine examination of fecal material give a positive diagnosis in only 5 to 15% of infected subjects,[8] and is therefore of little practical diagnostic use.[4] In a heavy infection, female pinworms may be adhere to stool that passes out through the anus, and they may thus be detected on the surface on the stool.[13][8] Adult pinworms are occasionally seen during colonoscopy.[8] On a microscopic level, pinworms have an identifying feature of alae (i.e., protruding ridges) running the length of the worm.[15]

Prevention

Prevention of pinworm infection is dependent on personal hygiene and the cleanliness of the living quarters.[16] Even so, infection may occur in the highest strata of society, where hygiene and nutritional status are typically high.[16] The stigma associated with pinworm infection is hence considered a possible over-emphasis.[16] Counselling is sometimes needed for upset parents that have discovered their children are infected, as they may not realize how prevalent the infection is.[13]

The rate of reinfection can be reduced through hygienic measures.[14] Hygienic measures are however often recommended, especially in recurring cases.[14] [16] This includes keeping fingernails short, and washing and scrubbing hands and fingers carefully, especially after defecation and before meals.[16][17] Under ideal conditions, bed covers, sleeping garments, and hand towels should be changed daily.[16] Simple laundering of clothes and linen disinfects them.[16] Children should wear gloves while asleep, and the bedroom floor should be kept clean.[16] Food should be covered to limit contamination with dust-borne parasite eggs.[16] Household detergents have little effect on the viability of pinworm eggs, and cleaning the bathroom with a damp cloth moistened with an antibacterial agent or bleach will merely spread the viable eggs.[16] Similarly, shaking clothes and bed linen will detach and spread the eggs.[16]

Treatment

Although hygiene plays a role, medication is the chief treatment.[16] Because the pharmaceutical drugs kill the adult pinworms but not the eggs, retreatment is recommended in two weeks.[14] If one household member spreads the eggs to another, it will be a matter of two or three weeks before those eggs become adult worms and thus amenable to treatment.[17] The benzimidazole compounds albendazole (brand names e.g., Albenza, Eskazole, Zentel and Andazol) and mebendazole (brand names e.g., Ovex, Vermox, Antiox and Pripsen) are the most effective.[16] They work by inhibiting the microtubule function in the pinworm adults, causing glycogen depletion,[16] thereby effectively starving the parasite.[17] A single 100 milligram dose of mebendazole with one repetition after a week, is considered the safest, and is usually effective with cure rate of 96%.[16][3] Mebendazole has no serious side effects, although abdominal pain and diarrhea have been reported.[16] Pyrantel pamoate (also called pyrantel embonate, brand names e.g., Reese's Pinworm Medicine, Pin-X, Combantrin, Anthel, Helmintox, and Helmex) kills adult pinworms through neuromuscular blockade,[17] and is considered as effective as the benzimidazole compounds.[4] Other medications are piperazine, which causes flaccid paralysis in the adult pinworms, and pyrvinium pamoate (also called pyrvinium embonate), which works by inhibiting oxygen uptake of the adult pinworms.[17] Pinworms located in the genitourinary system (in this case, female genital area) may require other drug treatments.[3]

Regardless of the medication used, reinfection is frequent.[3] Asymptomatic infections, often in small children, can serve as reservoirs of infection, and therefore the entire household should be treated regardless of whether or not symptoms are present.[4][16] Total elimination of the parasite in a household may require repeated doses of medication for up to a year or more.[4]

Notes


References

  • Hasegawa H, Ikeda Y, Fujisaki A, et al. (December 2005). "Morphology of chimpanzee pinworms, Enterobius (Enterobius) anthropopitheci (Gedoelst, 1916) (Nematoda: Oxyuridae), collected from chimpanzees, Pan troglodytes, on Rubondo Island, Tanzania". The Journal of Parasitology 91 (6): 1314–7. doi:10.1645/GE-569R.1. PMID 16539010. 
  • Nakano T, Okamoto M, Ikeda Y, Hasegawa H (December 2006). "Mitochondrial cytochrome c oxidase subunit 1 gene and nuclear rDNA regions of Enterobius vermicularis parasitic in captive chimpanzees with special reference to its relationship with pinworms in humans". Parasitology Research 100 (1): 51–7. doi:10.1007/s00436-006-0238-4. PMID 16788831. 
  • Hugot JP (1983). "[Enterobius gregorii (Oxyuridae, Nematoda), a new human parasite]" (in French). Annales de Parasitologie Humaine et Comparée 58 (4): 403–4. PMID 6416131. 
  • Hasegawa H, Takao Y, Nakao M, Fukuma T, Tsuruta O, Ide K (February 1998). "Is Enterobius gregorii Hugot, 1983 (Nematoda: Oxyuridae) a distinct species?". The Journal of Parasitology 84 (1): 131–4. doi:10.2307/3284542. PMID 9488350. 
  • Burkhart CN, Burkhart CG (October 2005). "Assessment of frequency, transmission, and genitourinary complications of enterobiasis (pinworms)". International Journal of Dermatology 44 (10): 837–40. doi:10.1111/j.1365-4632.2004.02332.x. PMID 16207185. 
  • Vanderkooi M (2000). Village Medical Manual (5th ed.). 

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