Etiology, Microbiology, and Pathogenesis of Scabies

Life Cycle and Morphology of Sarcoptes scabiei

Scabies is a contagious dermatological condition caused by the infestation of the skin by the ectoparasite Sarcoptes scabiei. It leads to intense pruritus and characteristic skin lesions due to the mite's burrowing activity and immune response.

Etiology

The primary causative agent, Sarcoptes scabiei, is an obligate parasite that completes its entire life cycle within the epidermis. Transmission occurs through direct skin contact, making close personal interaction the leading risk factor.

Microbiology

The mite has a round body with short legs, adapted for burrowing in the stratum corneum. It survives by consuming epidermal cells and secreting immunogenic proteins that contribute to inflammation.

Pathogenesis

• Burrowing and Egg Deposition: Female mites dig tunnels in the epidermis and lay eggs, which hatch within 3-4 days.
• Host Immune Response: The presence of mites, eggs, and excretions incites a delayed hypersensitivity reaction, leading to pruritus and erythematous papules.
• Secondary Infections: Persistent scratching can result in bacterial superinfection, commonly with Staphylococcus aureus.

Clinical Features

• Intense itching, predominantly at night
• Thin, linear burrows typically found in interdigital spaces
• Papules and nodules in immunocompromised individuals

Diagnosis and Management

Diagnosis relies on clinical examination and dermoscopic findings. Management includes topical scabicidal agents (permethrin, ivermectin) and hygiene measures to prevent reinfestation.