Chapter 21: Microbial Diseases of the Skin and Eyes

Microbial Diseases of the Skin and Eyes also introduces mucous membranes of the eyes and the role of tear enzymes like lysozyme in protecting against infection. The discussion then turns to bacterial infections of the skin, with particular attention to Staphylococcus aureus and Streptococcus pyogenes. S. aureus is implicated in folliculitis, impetigo, scalded skin syndrome, and toxic shock syndrome, while S. pyogenes causes erysipelas, necrotizing fasciitis, and streptococcal toxic shock syndrome. Virulence factors like coagulase, hyaluronidase, and exotoxins are emphasized. The chapter also covers Pseudomonas aeruginosa, a major cause of otitis externa (“swimmer’s ear”) and opportunistic infections in burn patients, along with its antibiotic resistance and characteristic blue-green pus due to pyocyanin production. Viral skin diseases discussed include warts (caused by papillomaviruses), smallpox and monkeypox, chickenpox and shingles (both from varicella-zoster virus), measles (rubeola), rubella (German measles), fifth disease, and roseola. Each disease’s transmission, pathogenesis, clinical signs, and prevention methods (especially vaccines) are explained. Fungal infections of the skin include cutaneous mycoses like ringworm and athlete’s foot caused by dermatophytes (Trichophyton, Epidermophyton, Microsporum), and subcutaneous infections like sporotrichosis. Candidiasis, primarily due to Candida albicans, is covered as a yeast infection of mucous membranes and skin folds, often opportunistic in immunocompromised patients. For the eyes, the chapter reviews conjunctivitis (pinkeye), most often caused by Haemophilus influenzae, Pseudomonas, or adenoviruses. It also explores inclusion conjunctivitis and trachoma caused by Chlamydia trachomatis, the latter being a leading cause of blindness worldwide. Other serious infections include herpetic keratitis (from HSV-1) and Acanthamoeba keratitis linked to contact lens use. By outlining the pathogens, symptoms, transmission routes, and treatments associated with skin and eye infections, this chapter reinforces the importance of hygiene, vaccination, and early clinical recognition in preventing disease and maintaining the integrity of the body’s outermost defenses.