What causes enterobiasis (pinworm infection)?

Causes of Pinworm Infection (Enterobiasis)

Pinworm infection (enterobiasis) is caused by the intestinal parasite Enterobius vermicularis, which is transmitted primarily through the fecal-oral route. 1, 2

Transmission Mechanisms

Primary Mode of Transmission

• Fecal-oral route: The most common way pinworms spread 1, 2
  • Eggs are transferred from the anus to the mouth through contaminated hands
  • Self-infection occurs when a person scratches the perianal area and then touches their mouth
  • Nail biting significantly increases risk (odds ratio 2.1) 2

Environmental Transmission

• Contaminated surfaces/fomites: Eggs can survive on:
  • Bedding and clothing
  • Toys
  • Household surfaces
  • Toilet seats 3
• Airborne transmission: Eggs are lightweight and can become airborne, then ingested when they settle on food or are directly inhaled 3

Risk Factors

• Age: Children aged 4-11 years are most commonly affected 4
• Living conditions:
  • Overcrowding (schools, daycare centers, family groupings) 5
  • Non-apartment dwellings (odds ratio 1.6) 2
• Behavioral factors:
  • Playing on the floor (odds ratio 2.5) 2
  • Poor hand hygiene before meals (odds ratio 1.7) 2
  • Inadequate personal hygiene 5
  • Uncontrolled anus-finger-mouth contact 4

Life Cycle of Enterobius vermicularis

1. Egg ingestion: Infection begins when microscopic pinworm eggs are swallowed
2. Larval development: Eggs hatch in the small intestine, releasing larvae
3. Adult worm maturation: Larvae mature into adult worms in the large intestine
4. Nocturnal migration: Female worms migrate to the perianal area at night to lay eggs
5. Egg deposition: Females deposit eggs on the perianal skin, causing itching
6. Reinfection cycle: Scratching transfers eggs to fingers, under nails, clothing, and bedding, facilitating reinfection 1

Epidemiology

• Worldwide distribution with higher prevalence in temperate regions 5
• Estimated prevalence in European children: approximately 20% 4
• Affects approximately 40 million people in the United States 6
• Occurs across all socioeconomic levels, though more common in lower socioeconomic groups 5
• Infants (<2 years) and adults are less commonly affected 4

Prevention Strategies

• Hand hygiene: Frequent handwashing with soap, especially before eating and after using the toilet 3
• Personal hygiene:
  • Wearing tight underwear both day and night
  • Daily changing of underwear
  • Keeping fingernails short and clean 2, 3
• Environmental cleaning:
  • Vacuuming or damp mopping bedroom floors
  • Washing bed linens and night clothes in hot water
  • Keeping toilet seats clean 3

Understanding the transmission cycle of pinworms is essential for effective treatment and prevention of reinfection, which is common due to the highly contagious nature of the parasite.