What is the most common causative organism for verruca vulgaris?

Explanation

## Correct Answer: A. Human papillomavirus – 2 Verruca vulgaris (common wart) is caused by **Human papillomavirus type 2 (HPV-2)**, the most frequent causative agent in Indian populations. HPV-2 is a non-oncogenic, low-risk HPV type that produces the characteristic hyperkeratotic, dome-shaped papules typically seen on hands, fingers, and knees. The virus infects the basal layer of epidermis and causes benign proliferation of keratinocytes, leading to the classic histological finding of acanthosis, hyperkeratosis, and parakeratosis. HPV-2 is transmitted through minor skin trauma and fomites, making it highly prevalent in school-age children and manual workers in India. The diagnosis is clinical, though HPV typing via PCR can confirm the causative type. Unlike HPV-16 and HPV-18 (high-risk oncogenic types), HPV-2 does not carry malignant potential and typically regresses spontaneously within 2–3 years, though treatment with salicylic acid, cryotherapy, or imiquimod may accelerate resolution. The distinction between HPV types is crucial for prognostication and counselling regarding malignant transformation risk. ## Why the other options are wrong **B. Human papillomavirus – 10** — HPV-10 is associated with **flat warts (verruca plana)**, not common warts. Flat warts present as small, flat-topped papules on the face, neck, and dorsal hands—morphologically and clinically distinct from the dome-shaped, hyperkeratotic lesions of verruca vulgaris. This is an NBE trap exploiting confusion between HPV types and their clinical phenotypes. **C. Human papillomavirus – 1** — HPV-1 is the causative agent of **plantar warts (verruca plantaris)**, which occur on weight-bearing surfaces of the sole and are often painful due to pressure. HPV-1 is not associated with common warts on hands and fingers. Students may confuse HPV-1 with HPV-2 if they recall only that both are non-oncogenic types without distinguishing their anatomical predilections. **D. Human papillomavirus – 3** — HPV-3 is associated with **flat warts and filiform warts**, not verruca vulgaris. HPV-3 produces morphologically different lesions and is less commonly encountered in Indian dermatology practice compared to HPV-2. Inclusion of HPV-3 tests whether students can differentiate HPV types by their clinical manifestations rather than memorizing a list. ## High-Yield Facts - **HPV-2** is the most common cause of verruca vulgaris (common wart) in Indian populations. - **HPV-1** causes plantar warts; **HPV-10** causes flat warts—each HPV type has distinct anatomical and morphological predilections. - **Non-oncogenic HPV types** (HPV-1, 2, 3, 10) do not carry malignant potential; high-risk types are HPV-16, 18, 31, 33. - Verruca vulgaris typically **regresses spontaneously in 2–3 years** without treatment; cryotherapy and salicylic acid are first-line therapies in India. - **Histology** of verruca vulgaris shows acanthosis, hyperkeratosis, parakeratosis, and koilocytes (HPV-infected cells with perinuclear halos). ## Mnemonics **HPV Type & Wart Location** **HPV-1** = Plantar (sole); **HPV-2** = Common (hands); **HPV-10** = Flat (face). Use: Recall which HPV causes which wart morphology by linking the number to the body part or appearance. **Low-Risk vs High-Risk HPV** **Low-risk (benign):** HPV-1, 2, 3, 10, 11 → warts, RRP. **High-risk (oncogenic):** HPV-16, 18, 31, 33 → cervical cancer, SCC. Use: When asked about malignant potential, recall that HPV-2 is low-risk. ## NBE Trap NBE pairs HPV-10 (flat warts) and HPV-1 (plantar warts) as plausible distractors to test whether students can differentiate HPV types by their clinical phenotypes rather than simply knowing "HPV causes warts." The trap exploits superficial knowledge of HPV without understanding type-specific anatomical predilections. ## Clinical Pearl In Indian school-age children and manual workers, verruca vulgaris caused by HPV-2 is so common that many parents seek treatment for cosmetic reasons or fear of spread, though reassurance about spontaneous regression and low malignant risk is often more appropriate than aggressive intervention. Cryotherapy with liquid nitrogen remains the most accessible and cost-effective first-line treatment in Indian primary care settings. _Reference: Robbins Ch. 25 (Infectious Diseases); Harrison Ch. 192 (Papillomavirus Infections); KD Tripathi Ch. 48 (Antivirals)_