Histopathology of Infectious Dermatoses

Overview / Definition Infectious dermatoses are skin conditions caused by infectious agents such as bacteria, viruses, fungi, and parasites. These conditions can range from superficial skin infections to deep-seated infections that may involve systemic illness. The histopathological examination of skin biopsies plays a pivotal role in identifying the underlying infectious agent and guiding appropriate management. Epidemiology The prevalence of infectious dermatoses varies globally and is influenced by factors such as geography, climate, and population density. Some key points include: Common bacterial infections include impetigo, cellulitis, and folliculitis. Fungal infections such as tinea corporis and candidiasis are prevalent in warm, humid climates. Viral infections like herpes simplex and varicella-zoster virus are widespread, particularly in children and immunocompromised individuals. Pathophysiology / Mechanism The pathophysiology of infectious dermatoses is characterized by the interaction between the host's immune response and the specific pathogenic organism. Key mechanisms include: Innate immune response: Initial defense against pathogens mediated by skin barrier, phagocytes, and antimicrobial peptides. Adaptive immune response: Involves T-cells and B-cells, leading to the production of antibodies against specific pathogens. Pathogen-specific mechanisms, such as the ability of certain bacteria to evade phagocytosis or fungal organisms to stimulate strong inflammatory responses. Clinical Presentation Clinical manifestations of infectious dermatoses can vary widely based on the causative agent. Common presentations include: Bacterial infections: Erythematous plaques, pustules, and crusting lesions seen in impetigo. Fungal infections: Annular erythematous lesions with scaling at the periphery in tinea. Viral infections: Vesicular lesions typical of herpes simplex and varicella. Parasitic infections: Papular urticaria or scabies presenting as pruritic papules