Viral Skin Infections

• Pathophysiology of common viral skin infections is caused by varicella-zoster virus (VZV), herpes simplex virus (HSV), and human papilloma virus (HPV).

Varicella-Zoster Virus (VZV)

• Belongs to the Herpesvirus family.
• Primary infection results in Varicella (chickenpox).
• The virus enters through the respiratory tract.
• It spreads hematogenously and infects epithelial cells of the skin.
• Causes vesicular lesions over the trunk, scalp, and face.
• Latency: The virus lies dormant in cranial nerve or dorsal root ganglia.
• Reactivation: Occurs due to stress, aging, or immunosuppression, resulting in Herpes Zoster (shingles).
• The virus travels down the sensory nerve to the skin, causing a painful vesicular rash in a dermatomal distribution.

Herpes Simplex Virus (HSV-1 and HSV-2)

• Is an enveloped DNA virus.
• HSV-1 is more commonly oral.
• HSV-2 is more commonly genital.
• Primary Infection: Enters through mucosal surfaces or broken skin.
• Replicates locally and travels retrograde to sensory ganglia, becoming latent.
• Reactivation trigger includes stress, UV light, and illness.
• The virus reactivates and travels back to the skin, causing recurrent vesicular lesions.
• Skin pathology results in a viral cytopathic effect that includes multinucleated giant cells, ballooning degeneration, and necrosis in the epidermis.

Human Papilloma Virus (HPV)

• Is a non-enveloped DNA virus with tropism for epithelial cells.
• Infection: Infects the basal layer of skin/mucosa via micro-abrasions.
• Integrates into host DNA, promoting keratinocyte proliferation.
• Forms warts (verrucae), which are benign epidermal tumors.
• Immune Evasion involves a limited inflammatory response allowing persistent infection.
• Oncogenic strains, such as HPV 16 and 18, can cause dysplasia and malignancy in mucosal sites, such as cervical cancer.

Chickenpox (Primary VZV Infection)

• Prodrome: Fever, malaise, and anorexia.
• Rash:
• Begins on the trunk and spreads to the face and extremities.
• Causes "dew drop on a rose petal" lesions (clear vesicles on an erythematous base).
• Lesions are in different stages: macules, papules, vesicles, and crusts.
• It is contagious 24 hours before the rash until crusting of lesions, which takes approximately 5–7 days.

Shingles (Herpes Zoster)

• Features localized pain (burning, tingling) in a dermatomal pattern.
• Followed by vesicular eruption on an erythematous base.
• Common sites are thoracic and trigeminal dermatomes.
• May lead to postherpetic neuralgia (chronic nerve pain).

Herpes Simplex Virus

• Primary infection involves painful grouped vesicles on an erythematous base.
• Often appears around the mouth (HSV-1) or genitals (HSV-2).
• Recurrent lesions are milder and may include tingling or burning prodrome.
• May ulcerate and crust over.

Human Papilloma Virus (HPV)

• Causes cutaneous warts:
• Verruca vulgaris: Common warts are firm, hyperkeratotic papules on the hands and fingers
• Verruca plantaris: Painful warts on the soles of the feet
• Verruca plana: Flat, smooth papules on the face and hands
• Causes mucosal warts: Condyloma acuminata are soft, pink, cauliflower-like growths in the genital/anal region.