Chapter 21: Sexually Transmitted Infections/Diseases

Sexually Transmitted Infections/Diseases microbiology chapter examines sexually transmitted infections and diseases, establishing the fundamental distinction between infection as the presence of a pathogen and disease as the manifestation of symptoms and tissue damage. The chapter traces the historical significance of STIs across civilizations and their continuing global impact, particularly through the AIDS pandemic. Bacterial STIs are presented as generally treatable with antibiotics, though delayed treatment can cause irreversible tissue scarring and infertility. Gonorrhea, caused by Neisseria gonorrhoeae, ranks among the most commonly reported STIs and demonstrates increasing antimicrobial resistance. Chlamydia trachomatis represents the most prevalent bacterial STI in the United States, frequently presenting asymptomatically while remaining a primary cause of pelvic inflammatory disease. Syphilis, caused by Treponema pallidum, progresses through three distinct clinical stages: primary manifestation with a chancre lesion, secondary stage involving systemic spread and rash, and tertiary complications featuring destructive granulomatous lesions affecting neurological and cardiovascular systems. The chapter also covers less frequent bacterial infections including chancroid and donovanosis. Viral STIs are examined as currently incurable conditions, though antiviral medications can suppress symptoms. HIV receives extensive coverage, explaining its mechanism of destroying helper T lymphocytes and compromising immune function, leading to susceptibility to opportunistic pathogens and malignancies such as Kaposi sarcoma. The text discusses HIV transmission routes, serological diagnosis using ELISA and Western blot techniques, and antiretroviral treatment strategies. Additional viral infections addressed include Hepatitis B, C, and D transmitted through sexual contact, genital herpes caused by HSV-1 and HSV-2, and Human Papillomavirus associated with genital warts and carcinogenesis, for which prophylactic vaccination is available. Fungal infections such as vulvovaginal candidiasis and balanitis, along with trichomoniasis as the sole protozoan STI, complete the pathogenic overview. The chapter concludes with epidemiological principles distinguishing prevalence from incidence, contextualizing the substantial public health burden of STIs.