STIs: Causes and Pathophysiology

• STIs are caused by various microorganisms and can lead to pelvic inflammatory disease (PID).

Causative Microorganisms of STIs

• HIV/AIDS is caused by the Human Immunodeficiency Virus (HIV), a retrovirus.
• Genital warts are primarily caused by Human Papillomavirus (HPV) types 6 and 11.
• Syphilis is caused by Treponema pallidum, an aerobic spirochete bacterium.
• Gonorrhea is caused by Neisseria gonorrhoeae, an aerobic Gram-negative diplococci.
• Chlamydia is caused by Chlamydia trachomatis, an obligate intracellular Gram-negative bacterium.

Pathophysiology of STIs

• HIV targets CD4+ T-helper cells, leading to immune dysfunction and progressive immunosuppression, which can cause opportunistic infections and malignancies.
• Herpes Simplex Virus (HSV) can cause primary, non-primary, and recurrent infections, enters sensory neurons, and becomes latent, leading to reactivations and recurrences.
• HSV-2 is commonly associated with genital infections and recurrent shedding.
• HPV infects basal epithelial cells through microabrasions, and high-risk types (e.g., 16, 18) can integrate into the host genome, disrupting tumor suppressor pathways (p53, Rb) and causing oncogenesis.
• Syphilis involves T. pallidum penetrating mucosal surfaces or skin, leading to systemic spread via lymphatics and forming granulomatous lesions (chancres) that progress through primary, secondary, and tertiary stages.
• Gonorrhea involves N. gonorrhoeae infecting columnar epithelium and can evade host immunity through pili and antigenic variation, potentially causing PID by ascending infection to the upper genital tract.
• Chlamydia has a two-part life cycle, transitioning from an extracellular "elementary body" to an intracellular "reticulate body", which triggers an inflammatory response, leading to scarring of mucosal tissues and potentially infertility or PID.

Clinical Manifestations of STIs

• HIV/AIDS: Male symptoms vary by stage, with an initial flu-like illness; female symptoms are the same, progressing to immunodeficiency.
• HSV: Males experience painful vesicular lesions (unilateral, crusting); females experience the same, but recurrent and milder over time.
• HPV: Males are often asymptomatic but may see warts; females are usually asymptomatic but may have genital warts or CIN.
• Syphilis: Symptoms depend on the stage (chancre, rash, gummas) in males, similar to females with possible systemic signs in later stages.
• Gonorrhea: Males experience dysuria and penile discharge; females are often asymptomatic but can progress to PID.
• Chlamydia: Males are 90% asymptomatic but may have dysuria and penile discharge; females may have a friable cervix, spotting, and infertility.

Relationship Between STIs and Pelvic Inflammatory Disease (PID)

• STIs are primary causes of PID, specifically Chlamydia and Gonorrhea.
• The mechanism involves infection ascending from the cervix to the uterus, fallopian tubes, and ovaries, leading to inflammation, scarring, adhesions, and potentially infertility or ectopic pregnancy.
• Chlamydia is implicated in preventable infertility and ectopic pregnancy due to silent progression.
• Gonorrhea may lead to Fitz-Hugh-Curtis Syndrome (perihepatitis).

STI Summary Table

• HIV/AIDS: Caused by Human Immunodeficiency Virus (HIV), infects the blood and immune system (CD4+ T cells), transmitted through blood, semen, vaginal fluids, and breast milk; key features include immunosuppression, opportunistic infections, weight loss, and fever; complications include AIDS, opportunistic infections, and cancers (e.g., Kaposi sarcoma).
• Genital Warts (HPV): Caused by Human Papillomavirus (HPV) types 6 & 11 (warts), 16 & 18 (cancer), infects genital skin and mucosa (external genitalia, cervix, anus), transmitted through skin-to-skin contact, especially during intercourse; key features include genital warts (painless) and cervical dysplasia/cancer; complications include cervical, anal, and oropharyngeal cancers (high-risk types).
• Syphilis: Caused by Treponema pallidum (spirochete bacterium), infects the genital mucosa, skin, and systemically via blood/lymph, transmitted through direct contact with a chancre or vertical transmission; key features include a painless chancre (primary), rash (secondary), and systemic involvement (tertiary); complications include neurosyphilis, cardiovascular damage, and congenital syphilis.
• Gonorrhea: Caused by Neisseria gonorrhoeae (Gram-negative diplococcus), infects the cervix, urethra, rectum, pharynx, and conjunctiva, transmitted through sexual contact, vertical transmission, and rarely via fomites; key features include purulent discharge, dysuria, pelvic pain, and PID in women; complications include PID, infertility, ectopic pregnancy, and perihepatitis (Fitz-Hugh-Curtis).
• Chlamydia: Caused by Chlamydia trachomatis (obligate intracellular bacterium), infects the cervix, urethra, rectum, eyes (neonatal), and fallopian tubes, transmitted through sexual and vertical transmission; key features include often asymptomatic, discharge, PID, infertility, neonatal conjunctivitis; complications include PID, infertility, ectopic pregnancy, and neonatal pneumonia/conjunctivitis.
• Herpes Simplex Virus: Caused by Herpes Simplex Virus (HSV-1 and HSV-2), infects external genitalia, buttocks, perianal area, thighs, and oral mucosa, transmitted through direct contact with lesions or infected secretions; key features include painful vesicles, recurrent outbreaks, and systemic flu-like symptoms initially; complications include neonatal herpes, encephalitis, and recurrent painful outbreaks.