Pathophysiology and Treatment of Enterobiasis
Pathophysiology
Enterobiasis is caused by Enterobius vermicularis (pinworm/threadworm), which has a 2-6 week prepatent period and transmits via the faeco-oral route, primarily through ingestion of eggs from self-infection, oral-anal contact, or contaminated surfaces/fomites. 1
Transmission Cycle and Mechanism
- Self-infection is the most common mode of transmission, occurring when eggs deposited in the perianal area are transferred to the mouth via contaminated hands or fomites 1
- The infection is worldwide in distribution and particularly affects children, with higher prevalence in schools, institutions, and family groupings due to overcrowding and inadequate hygiene 1, 2
- After ingestion, eggs hatch in the small intestine, mature to adults, and female worms migrate to the perianal region at night to deposit eggs, causing the characteristic symptoms 2
Clinical Manifestations
- Most cases are asymptomatic, but when symptomatic, the hallmark is intense pruritus ani (perianal itching) 1
- Additional symptoms may include weight loss, irritability, diarrhea, abdominal pain, and occasionally colitis with eosinophilia 1
- Ectopic migration can occur, with worms entering the female genital tract causing vulvovaginitis, vaginal discharge, or rarely granulomas of the uterus, ovary, fallopian tubes, and pelvic peritoneum 1, 2
- Scratching may lead to skin irritation, eczematous dermatitis, hemorrhage, or secondary bacterial infections 2
Diagnosis
Diagnosis is made by the "sellotape test" (cellulose tape test), performed by placing the sticky side of tape on the perianal skin and examining it microscopically for ova. 1
- Concentrated stool microscopy or fecal PCR are alternative diagnostic methods 1
- Eggs are only eliminated intermittently, so repeat specimens should be examined to increase diagnostic yield 1
- Direct microscopic examination may reveal adult worms but sometimes no eggs, particularly in ectopic infections 3
Treatment
First-Line Pharmacotherapy
The recommended treatment is albendazole 400 mg orally as a single dose OR mebendazole 100 mg orally as a single dose. 1
- Albendazole 400 mg PO single dose is the preferred option per the most recent UK guidelines 1
- Mebendazole 100 mg PO single dose is an equally effective alternative 1
- The FDA approves mebendazole for treatment of E. vermicularis with a 95% cure rate 4
Extended Treatment for Complicated Cases
For recurrent or ectopic enterobiasis (such as vaginal involvement), extended treatment is necessary: albendazole 400 mg PO twice daily for 21 days with monitoring of liver function and full blood count. 1
- This extended regimen is based on expert opinion for cases where standard single-dose therapy fails 1
- Mebendazole 100 mg for 3 days followed by two more courses at 3-week intervals has been used successfully in recurrent vaginal enterobiasis 3
Treatment of Household Contacts
All close family members should be treated simultaneously when a confirmed case exists, as the infection spreads easily within households 2, 5
- Retreatment should be given after a two-week interval to ensure eradication of parasites that may have been in the egg stage during initial treatment 5
- Mass medication of affected groups (schools, institutions) reduces symptoms rapidly and cost-effectively 2
Important Clinical Considerations
Common Pitfalls
- Do not rely solely on stool examination, as eggs are deposited perianally rather than in feces; the sellotape test is far more sensitive 1
- Do not assume treatment failure means drug resistance; reinfection or incomplete treatment of household contacts is more likely 3, 5
- Consider ectopic infection in females with vulvovaginal symptoms even in the absence of gastrointestinal complaints, as the vagina can serve as a reservoir 3
Special Populations
- In cases of peritoneal enterobiasis mimicking endometriosis, mebendazole treatment resolves symptoms and peritoneal deposits 6
- Treatment is safe and effective in children, who are the most commonly affected population 1, 2