What causes pinworms in adults?

Pinworm Infection in Adults: Causes and Transmission

Pinworm infection (enterobiasis) in adults is primarily caused by the intestinal parasite Enterobius vermicularis, which is transmitted through the fecal-oral route when eggs are transferred from the anus to the mouth via contaminated hands. 1

Primary Modes of Transmission

Direct Transmission

• Fecal-oral route: The most common transmission method occurs when a person scratches the perianal area (often due to itching caused by female worms laying eggs) and then touches their mouth, transferring eggs 1
• Self-infection (autoinfection): Occurs when a person scratches the perianal area and reinfects themselves 1

Environmental Transmission

• Contaminated surfaces: Eggs can survive on bedding, clothing, toys, household surfaces, and toilet seats 1
• Airborne transmission: Though less common, eggs can become airborne and be ingested when they settle on food or are directly inhaled 1, 2

Risk Factors for Pinworm Infection

Several behaviors and environmental factors increase the risk of pinworm infection in adults:

• Playing or sitting on contaminated floors (2.5× higher risk) 1
• Nail biting (2.1× higher risk) 1
• Poor hand hygiene, especially before meals (1.7× higher risk) 1
• Living in non-apartment dwellings (1.6× higher risk) 1
• Poor socioeconomic conditions and inadequate sanitation 3
• Overcrowded living conditions 3, 4
• Close contact with infected individuals, particularly in household settings 3

Life Cycle and Infection Process

1. Ingestion: The infection begins when pinworm eggs are ingested
2. Larval development: Larvae develop in the small intestine
3. Maturation: Adult worms mature in the large intestine
4. Egg deposition: Female worms migrate to the perianal area at night to lay eggs
5. Reinfection: Scratching due to itching transfers eggs to fingers, under nails, clothing, and bedding 1

Prevention Strategies

To prevent pinworm infection, adults should:

• Wash hands thoroughly with soap, especially before eating and after using the toilet 1, 5
• Keep fingernails short and clean 1
• Wear tight underwear and change it daily 1
• Regularly clean bedroom floors by vacuuming or damp mopping 5
• Wash bed linens and night clothes in hot water 5
• Keep toilet seats clean 5

Treatment Approaches

For adults with confirmed pinworm infection:

• First-line treatment: Mebendazole 100 mg or albendazole 400 mg as a single dose, repeated in 2 weeks 1, 3
• For pregnant women: Pyrantel pamoate (11 mg/kg, maximum 1 g) is preferred due to its safety profile 1, 3
• All household members should be treated simultaneously to prevent reinfection 3

Important Clinical Considerations

• Approximately 30-40% of infected individuals are asymptomatic 3
• The most common symptom is nocturnal perianal itching 3
• Diagnosis is best established by the cellophane tape test, with sensitivity of ~50% for a single test and ~90% for three consecutive morning tests 1, 3
• Recurrence is common despite effective treatment, usually due to reinfection 3

By understanding these transmission mechanisms and implementing proper hygiene practices, adults can effectively prevent and manage pinworm infections.