What causes warts in children?

What Causes Warts in Children

Warts in children are caused by infection of skin cells (keratinocytes) with human papillomavirus (HPV), transmitted through direct contact with infected individuals or contaminated surfaces, with the virus remaining infectious in the environment for months to years. 1

Viral Etiology

• The majority of common warts in children are caused by HPV types 1,2,4,27, or 57, with HPV-1 and HPV-2 being the most frequent culprits. 1, 2
• Flat warts (verruca plana) are typically caused by HPV types 3 or 10. 1
• Verruca vulgaris (common warts) are principally caused by HPV 2 and HPV 4, most commonly observed on children's hands and fingers. 1
• Recent research shows that HPV subtypes 2,27,57, and 63 are particularly common in pediatric populations. 3
• There are over 150 genotypically different types of HPV, classified based on viral DNA variation. 1

Mechanism of Infection

• HPV infects keratinocytes at the basal layer of the epidermis, leading to clonal proliferation that eventually produces a visible wart weeks or even months after initial infection. 1
• The infection causes epidermal thickening and hyperkeratinization, resulting in the characteristic raised, rough appearance of warts. 1, 2

Transmission Routes

Direct and Environmental Spread

• HPV spreads from person to person through direct skin contact or via contaminated environmental surfaces. 1
• The virus can persist outside the body for months or possibly years (similar to bovine papillomavirus), making environmental transmission significant. 1, 2

Family and School Transmission

• Having family members with warts increases a child's risk 2-fold (hazard ratio 2.08), making household transmission a major route of infection. 4
• Wart prevalence in the classroom independently increases risk by 20% for every 10% increase in affected classmates (hazard ratio 1.20 per 10% increase). 4
• Studies show HPV carriage on normal skin is higher in children with active warts and their family members. 3

Autoinoculation

• Children can spread warts to other parts of their own body through autoinoculation, such as transferring virus from fingers to mouth. 1

Epidemiology in Children

• Warts are extremely common in childhood, affecting 5-30% of children and young adults, with infection most prevalent in the second decade of life (affecting over 40% of children). 1, 3
• Children with white skin type have a 2.3-fold increased risk of developing warts compared to darker skin types. 4
• The incidence rate is approximately 29 per 100 person-years at risk in primary school-aged children. 4

Natural History

• Spontaneous clearance occurs in half of children within 1 year and two-thirds by 2 years, as the immune system develops cell-mediated and humoral immunity against HPV. 1, 2, 5
• However, as many as one-third of children will have persistent HPV infection beyond 2 years. 5
• Warts can persist for years with little or no inflammation before spontaneous regression occurs. 1

Common Pitfalls

• Public places like swimming pools are often blamed for wart transmission, but family and classroom exposure are the primary risk factors that should be addressed in prevention strategies. 4
• Preventive recommendations should focus on limiting HPV transmission within families and school classes rather than avoiding public facilities. 4
• Unusually severe or prolonged warts should prompt consideration of underlying immune deficiency, as warts may be a presenting feature of immunosuppressed states. 1