Chapter 46: Sexually Transmitted Infections – Causes & Effects

Infections primarily affecting the external genitalia include Condylomata Acuminata (genital warts) caused by HPV, where high-risk strains (e.g., types 16 and 18) are associated with cervical dysplasia and cancer. Genital Herpes (typically HSV-2, sometimes HSV-1) is characterized by painful, recurrent vesicular lesions resulting from the virus’s neurotropic property and ability to establish latency within the sacral dorsal root ganglia before reactivation. The chapter also addresses less common external infections like Chancroid, Granuloma Inguinale, and Lymphogranuloma Venereum (LGV). Regarding vaginal conditions, only Trichomoniasis (caused by the anaerobic protozoan T. vaginalis) is a confirmed STI requiring partner treatment, presenting often with a copious, frothy, malodorous green or yellow discharge, and acting as a risk factor for HIV transmission. Conversely, Candidiasis (yeast infection) and Bacterial Vaginosis (BV) are usually symptomatic due to ecological changes in the vaginal flora rather than direct sexual transmission. BV, the most common vaginal infection, involves a shift from protective lactobacilli, resulting in a thin, foul, fishy-smelling grayish-white discharge without significant inflammation. The most serious systemic STIs include Chlamydial infections (C. trachomatis), the most prevalent STI reported in the United States, which often lacks specific symptoms but can lead to severe pelvic inflammatory disease (PID) or Reiter syndrome. Gonorrhea (N. gonorrhoeae) frequently develops antibiotic resistance, requiring dual therapy (e.g., ceftriaxone and azithromycin) to combat spreading infection that can cause systemic involvement of the heart and joints. Syphilis (T. pallidum) progresses through distinct stages, starting with the primary painless, indurated chancre, moving to a secondary stage characterized by systemic symptoms and a rash (often on the palms/soles), and potentially culminating in decades later in destructive tertiary lesions called gummas or cardiovascular/CNS damage. Finally, the chapter highlights the Zika virus, transmitted sexually and by mosquitoes, emphasizing the critical risk it poses to unborn fetuses by causing severe birth defects, such as microcephaly, with prevention being crucial since no cure or vaccine currently exists.