• Caused by the intestinal nematode Enterobius vermicularis
• Most common worm infection in the U.S. and Western Europe
• Causes anal pruritus, primarily in young children

Epidemiology

• Prevalence
  • 20–40 million people are estimated to be infected in the U.S.
  • ~300 million people are infected worldwide.
• Age
  • Schoolchildren account for a disproportionate number of cases.
  • Pinworm infection is rare in children < 2 years of age.
• Geographic distribution
  • Endemic worldwide
  • As common in temperate countries as in the tropics

Risk Factors

• Transmission occurs in all socioeconomic groups.
• Risk factors include:
  
  • Poor fecal sanitation
  • Poor personal hygiene (i.e., inadequate hand washing)
  • Prolonged residence in an endemic area

Etiology

• Enterobius vermicularis
  • Intestinal nematode (roundworm)
  • Adult worms are ~1 cm long and dwell in the bowel lumen (cecum, appendix).
  • The gravid female worm migrates nocturnally out into the perianal region and releases up to 10,000 immature eggs.
  • Eggs become infective within hours.
  • Larvae hatch and mature entirely within the intestine.
  • Life cycle: ~1 month
  • Adult worms survive for ~2 months.
• Transmission
  • Transmitted by hand-to-mouth passage of infective eggs
  • Self-infection results from perianal scratching and transport of infective eggs on the hands or under the nails to the mouth.
  • Person-to-person transmission
    • Common among family members and institutionalized populations
    • Eggs can survive up to 2 weeks on clothing, bedding, or other objects.
  • Incubation period (time from infection to egg production by mature female worm): 35–45 days
  • Significant protective immunity appears not to develop.

Symptoms & Signs

• Most infections are asymptomatic.
• In symptomatic individuals, most clinical manifestations are due to perianal irritation, allergic reactions, or ectopic migration of worms.
• Perianal pruritus (pruritus ani) is the cardinal symptom.
• Itching often is worse at night because of nocturnal migration of the female worms.
• Heavy infections may cause:
  • Anorexia
  • Weight loss
  • Abdominal pain
  • Restlessness and insomnia
  • Ectopic migration to other sites, leading to complications (salpingitis, oophoritis, peritonitis)

Differential Diagnosis

• Perianal pruritus from other causes
  • Mycotic infections: tinea or candidiasis
  • Contact dermatitis
  • Hemorrhoids
  • Proctitis
  • Anal fissure
  • Genital herpes

Diagnostic Approach

• The diagnosis is based on the finding of characteristic eggs in the perianal region.
  • Cellulose acetate (cellophane) tape test
    • Tape is pressed against the perianal skin.
    • Test is best done upon awakening and prior to bathing and defecation.
    • Three specimens must be obtained to achieve a sensitivity of 90%.
• Eggs usually are not found in feces.
  • Thus stool examination for ova and parasites has a low yield.
• Occasionally, adult pinworms can be visualized in the perianal area or by anoscopy or colonoscopy.

Laboratory Tests

• Microscopic examination
  • Cellulose tape is transferred to a microscope slide.
  • Low-power examination reveals the characteristic pinworm eggs, which are:
    • Oval
    • 55 × 25 μm
    • Flattened along one side

Imaging

• Not indicated
  

Diagnostic Procedures

• Cellulose tape test
  • Eggs in the perianal region are detected by application of cellulose acetate tape in the morning before washing or defecation.
  • Tape is placed on a glass slide and examined under a microscope.
• Occasionally, adult pinworms may be visualized in the perianal area or via anoscopy or colonoscopy.

Treatment Approach

• Medical treatment of all affected individuals and their household contacts with antiparasitic agents is the modality of choice.
• Treatment of household members also is advocated to eliminate asymptomatic reservoirs of potential reinfection.

Specific Treatments

Antihelmintic therapy

• Agents
  • Mebendazole (100 mg PO once) or
  • Albendazole (400 mg PO once for patients > 2 years of age) or
  • Pyrantel pamoate (11 mg/kg of base PO once; maximum, 1 g)
• Schedule
  • Two-dose treatment, with the second dose given after 10–14 days

Reinfection

• Antiparasitic therapy
  • Infected individuals should be re-treated with a two-dose regimen, as described above.
  • Playmates, schoolmates, close contacts outside the home, and household members should be considered for two-dose treatment at the same time.
• Other measures
  • All bedding and clothing should be washed.
  • Additional measures should include frequent hand washing and clipping of fingernails to decrease ongoing transmission and reinfection.

Monitoring

• No specific monitoring is required unless symptoms recur after treatment.
  • Recurrence warrants repeated evaluation and re-treatment.

Complications

• Itching may lead to excoriation and bacterial superinfection.
• Rarely, adult worm migration may cause:
  • Inflammatory conditions such as vulvovaginitis, diverticulitis, salpingitis, or oophoritis
  • Granulomatous reactions of the colon, genital tract, or peritoneum
• Although adult pinworms have been found in normal and inflamed appendices, it is not entirely clear whether they play a pathogenic role in the development of appendicitis.
• Allergic reactions

Prognosis

• Infection usually is benign.
• Cure rates of > 95% are achieved with drug therapy.
• Reinfection is common.

Prevention

• Infection or reinfection may be prevented by:
  • Frequent bathing
  • Using clean underclothing, night clothes, and bed sheets
  • Routine hand washing, particularly after defecation
  • Keeping fingernails short and clean
  • Instructing children not to scratch the buttock area or bite their nails

ICD-9-CM

• 127.4 Enterobiasis (includes pinworm infection)

See Also

• Strongyloidiasis

Internet Sites

• Professionals
  • Enterobiasis
    Centers for Disease Control and Prevention
  • Homepage
    National Institute of Allergy and Infectious Diseases
    
• Patients
  • Pinworm Infection
    U.S. Centers for Disease Control and Prevention
  • Parasitic Roundworm Diseases
    U.S. National Institute of Allergy and Infectious Diseases

General Bibliography

• Arca MJ et al: Clinical manifestations of appendiceal pinworms in children: an institutional experience and a review of the literature. Pediatr Surg Int 20:372, 2004  [PMID:15141320]
• Chan MS: The global burden of intestinal nematode infections--fifty years on. Parasitol Today 13:438, 1997  [PMID:15275146]
• Cowden J, Hotez P: Mebendazole and albendazole treatment of geohelminth infections in children and pregnant women. Pediatr Infect Dis J 19:659, 2000  [PMID:10917227]
• Gyorkos TW et al: Intestinal parasite infection in the Kampuchean refugee population 6 years after resettlement in Canada. J Infect Dis 166:413, 1992  [PMID:1634813]
• Horton J: Albendazole: a broad spectrum anthelminthic for treatment of individuals and populations. Curr Opin Infect Dis 15:599, 2002  [PMID:12821837]
• Petro M et al: Unusual endoscopic and microscopic view of Enterobius vermicularis: A case report with a review of the literature. South Med J 98:927, 2005
  
• St Georgiev V: Chemotherapy of enterobiasis (oxyuriasis). Expert Opin Pharmacother 2:267, 2001  [PMID:11336585]
• This topic is based on Harrison’s Principles of Internal Medicine, 16th edition, chapter 201, Intestinal Nematodes by PF Weller and TB Nutman.
  

PEARLS

• Pinworm infection is the most common helminthic infection worldwide.
  • There is no significant difference in prevalence between temperate and tropical regions.
• Although pruritus ani is the most common clinical manifestation, complications such as eosinophilic enterocolitis, salpingitis, and peritoneal inflammation have been described.
• Despite high cure rates with antiparasitic agents, reinfection is common, and all household contacts must receive simultaneous treatment.