Helminth

Pinworm

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Pinworm, Enterobius vermicularis, Enterobiasis

  • See Also
  1. Helminth
  2. Parasitic Infection
  • Epidemiology
  1. Most common in children ages 5 to 14 years
  2. Most common Helminth infection in the United States (Incidence as high as 40 million/year)
  3. Prevalence: 209 million children infected worldwide
    1. Worldwide, 30% of children are infected
  • Pathophysiology
  1. Intestinal roundworm (nematode) infection
    1. Humans are only known host
  2. Life Cycle
    1. Enterobious eggs are ingested
      1. Larvae hatch in duodenum
    2. Worms live in ascending colon at cecum
      1. Female worms migrate to anus and perineum at night to deposit eggs
      2. May lay up to 15,000 eggs nightly
    3. Majority of eggs dry-out within 3 days
      1. However Pinworm eggs may have as much as a 20 day external viability
  3. Transmission
    1. Scratching of perianal or perineal Pruritus results in transmission of eggs to fingers
      1. Further transmission to other fomites (bedding, clothing)
    2. Ingestion of Pinworm ova
      1. Fecal-oral transmission of eggs
      2. Passed by direct contact or fomites (hands, clothing, house dust)
  • Risk Factors
  1. Family transmission in crowded environments
    1. Children and their Caregivers
  2. Caregivers of institutionalized patients
  3. Rural setting
  4. Younger age
  5. Male gender
  • Symptoms
  1. Often asymptomatic
  2. Perianal or perineal Pruritus worse at night
  3. May also cause vaginal irritation
  4. Restlessness at night
  • Signs
  1. See Pinworm Test (Cellophane Tape Test)
  2. Small (0.5 to 1 cm) white worms at perianal area
  • Differential Diagnosis
  1. See Pruritus Ani
  2. See Pruritus Vulvae
  • Labs
  1. Pinworms are not found in the stool
  2. Pinworm Test
    1. Best yield at night or early morning
  • Course
  1. Self limited; resolves by 6 weeks (unless reingested)
  • Management
  1. Pyrantel Pamoate (Pin-Rid, OTC)
    1. Dose: 11 mg/kg up to 1 gram PO for 1 dose (age 2 or older)
    2. Repeat dose in 2 weeks
    3. Avoid in pregnancy or age under 2 years old
    4. Available as over-the-counter medication, and only $20 per 2 dose course
    5. Cure rates >90%
  2. Mebendazole (Vermox, Emverm)
    1. Dose: 100 mg chewable for 1 dose (age 2 or older)
    2. Repeat dose in 2 weeks (per CDC and despite package insert)
    3. Avoid in first trimester of pregnancy or age under 2 years old
    4. Was not available as of 2012, and available as of 2016 at $740/course
    5. Cure rates >90%
  3. Albendazole (Valbazen, Albendazole)
    1. Age >=2 years: 400 mg orally for 1 dose
    2. Age <2 years: 200 mg orally for 1 dose
    3. Repeat dose in 2 to 3 weeks
    4. Avoid in first trimester of pregnancy (or age under 1 year old)
    5. As with Mebendazole, very expensive in U.S. (>$600/course)
  • Management
  • Other measures
  1. Treat household contacts (esp. if 2 or more members affected)
    1. Reinfection is common
  2. Encourage Hand Washing and morning shower or bath
  3. Clean all linen, clothing in hot water (eggs survive 2-3 weeks on objects)
  • Complications
  1. Secondary localized Bacterial Infections
    1. Due to Pruritus, scratching and localized inflammation
  2. Appendicitis (rare)
    1. May complicate chronic Pinworm infections
  • Prevention
  1. Hand Hygiene is the most effective overall prevention measure
  • References
  1. Gilbert et al (2016) Sanford Guide to Antimicrobial Therapy, accessed IOS app 5/4/2016
  2. Kazura in Behrman (2000) Nelson Pediatrics, p. 1067-8
  3. (2016) Presc Lett 23(5): 28
  4. (2012) Presc Lett 19(3): 16
  5. Markell (1985) Pediatr Clin North Am 32(4):971-86 [PubMed]
  6. Pyzocha (2023) Am Fam Physician 108(5): 487-93 [PubMed]
  7. Schonoau (2024) Am Fam Physician 109(6): 569-70 [PubMed]