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Pinworms
Jonathan MacClements, MD, FAAFP
image BASICS
DESCRIPTION
  • Intestinal infection with Enterobius vermicularis
    • Characterized by perineal and perianal itching
    • Usually worse at night
  • System(s) affected: gastrointestinal; skin/exocrine
  • Synonym(s): enterobiasis
EPIDEMIOLOGY
Predominant age: 5 to 14 years
Prevalence
  • Most common helminthic infection in the United States
    • 20 to 42 million people harbor the parasite
  • ˜30% of children are infected worldwide.
Pediatric Considerations
More common in children, who are more likely to become reinfected.
ETIOLOGY AND PATHOPHYSIOLOGY
  • Small white worms (2 to 13 mm) inhabit the cecum, appendix, and adjacent portions of the ascending colon following ingestion.
  • Female worms migrate to the perineal areas at night to deposit eggs; this causes local irritation and itching.
  • Scratching leads to autoingestion of the eggs and continuation of pinworm's life cycle within the host. Eggs incubate 1 to 2 months in the host small intestine. When mature, female pinworms migrate to the colon where they lay eggs around the anus at night and the lifecycle continues.
  • Infestation by the intestinal nematode E. vermicularis
RISK FACTORS
  • Institutionalization
  • Crowded living conditions
  • Poor hygiene
  • Warm climate
  • Handling of infected children's clothing or bedding
GENERAL PREVENTION
  • Hand hygiene, especially after bowel movements
  • Clip and maintain short fingernails.
  • Wash anus and genitals at least once a day, preferably during shower.
  • Avoid scratching anus and putting fingers near nose (pinworm eggs can also be inhaled) or mouth.
COMMONLY ASSOCIATED CONDITIONS
Pruritus ani
image DIAGNOSIS
PHYSICAL EXAM
Perineal and perianal exam. Particularly in early morning to look for evidence of migrating worms.
DIFFERENTIAL DIAGNOSIS
  • Idiopathic pruritus ani (1)[A]
  • Atopic dermatitis, contact dermatitis
  • Psoriasis; lichen planus
  • Human papillomavirus (HPV)
  • Herpes simplex virus (HSV)
  • Fungal infections; erythrasma
  • Scabies
  • Vaginitis; hemorrhoids
DIAGNOSTIC TESTS & INTERPRETATION
  • Adhesive tape test (2)[A]
    • Place cellophane tape on the perianal skin in the early morning before bathing and affixed to a microscope slide to look for pinworm eggs.
    • If performed on three consecutive mornings, this test has 90% sensitivity
    • Alternatively, anal swabs or a pinworm paddle coated with adhesive material can be useful.
    • Scrapings from under fingernails of affected individuals can reveal pinworm eggs.
  • Digital rectal exam with saline slide preparation of stool on gloved finger
  • Stool samples are not helpful.
  • Routine stool examination for ova and parasites is positive in only 10-15% of infected patients.
Test Interpretation
Identification of ova on low-power microscopy or direct visualization of the female worm (10-mm long); ova are asymmetric, flat on one side, and measure 56 × 27 &mgr;m.
image TREATMENT
MEDICATION
First Line
  • Treatment options include:
    • Mebendazole (Vermox): chewable 100-mg tablet as a single dose in adults and children >2 years of age; may repeat in 2 to 3 weeks; use with caution in children <2 years of age (3,4)[A].
    • Albendazole (Albenza): 400 mg PO as a single dose in adults and children >2 years of age; may repeat in 2 to 3 weeks; 200 mg PO as a single dose repeated in 7 days in children ≤2 years of age (3,4)[A].
    • P.803

    • Pyrantel pamoate (Pin-X, Reese's Pinworm Medicine): oral liquid or tablet 11 mg/kg as a single dose in adults and children >2 years of age; maximum dose 1 g. Use with caution in children <2 years of age (3,4)[A].
  • Repeat treatment after 2 weeks is often recommended due to the high frequency of reinfection. Refractory cases may (rarely) require retreatment every 2 weeks for 4 to 6 cycles.
  • All symptomatic family members should be treated.
Pregnancy Considerations
Avoid drug therapy in pregnancy. Treat after delivery. Breastfeeding is OK during mebendazole therapy (3,4)[A].
image ONGOING CARE
FOLLOW-UP RECOMMENDATIONS
Unnecessary unless symptoms recur after initial therapy
PATIENT EDUCATION
  • Take medicine with food.
  • Practice good hygiene: hand washing and perianal hygiene; particularly after bowel movements
  • Encourage frequent and careful hand washing.
  • Clip fingernails.
  • Wash clothing and bedding after diagnosis to prevent reinfection. Do not shake linen and clothing before laundering because this may spread the eggs.
  • Do not share washcloths.
  • Do not allow children to cobathe during treatment and for 2 weeks after; showering is preferred.
PROGNOSIS
  • Asymptomatic carriers are common.
  • Drug therapy is 90% curative.
  • Reinfection is common, especially among children.
REFERENCES
1. Stermer E, Sukhotnic I, Shaoul R. Pruritus ani: an approach to an itching condition. J Pediatr Gastroenterol Nutr. 2009;48(5):513-516.
2. Kucik CJ, Martin GL, Sortor BV. Common intestinal parasites. Am Fam Physician. 2004;69(5):1161-1168.
3. Enterobius vermicularis. In: Drugs for Parasitic Infections. Treatment guidelines from The Medical Letter. New Rochelle, NY: The Medical Letter, Inc.; 2010;8(Suppl). www.cdc.gov/parasites/pinworm/health_professionals/index.html
4. Dennie J, Grover SR. Distressing perineal and vaginal pain in prepubescent girls: an aetiology. J Paediatr Child Health. 2013;49(2):138-140.
5. Kashyap B, Samantray JC, Kumar S, et al. Recurrent paediatric pinworm infection of the vagina as a potential reservoir for Enterobius vermicularis. J Helminthol. 2014;88(3):381-383.
Additional Reading
&NA;
Hamblin J, Connor PD. Pinworms in pregnancy. J Am Board Fam Pract. 1995;8(4):321-324.
See Also
&NA;
Pruritus Ani
Codes
&NA;
ICD10
B80 Enterobiasis
Clinical Pearls
&NA;
  • Nocturnal or early morning perianal itch with restless sleep or insomnia (particularly in children), is hallmark of symptomatic pinworm infection.
  • Treatment includes of mebendazole, albendazole, or pyrantel pamoate.
  • Treat close contacts.
  • Retreatment after 2 weeks is typically recommended.