Sexually Transmitted Infections

STI Overview - The Unwanted Guests

• Classification & Key Pathogens:
  • Bacterial: Gonorrhea (N. gonorrhoeae), Syphilis (T. pallidum), Chlamydia (C. trachomatis)
  • Viral: HIV, HSV, HPV, Hepatitis B/C
  • Protozoal: Trichomoniasis (T. vaginalis)
  • Fungal: Candidiasis (often via sexual contact)
  • Ectoparasitic: Scabies, Pubic lice
• Transmission Routes:
  • Primarily sexual contact (vaginal, anal, oral).
  • Vertical (mother-to-child).
  • Bloodborne (needles, transfusions).
• Lab Diagnosis Pillars:
  • Microscopy (e.g., Gram stain, wet mount).
  • Culture (bacterial, fungal).
  • NAATs (e.g., PCR for Chlamydia, Gonorrhea - high sensitivity/specificity).
  • Serology (antibodies/antigens for Syphilis, HIV).

⭐ NAATs are the preferred diagnostic method for Chlamydia trachomatis and Neisseria gonorrhoeae due to high sensitivity.

Bacterial Bad Boys - Germ Warfare

• Syphilis (Treponema pallidum - spirochete):

  • Pathogenesis: Penetrates mucosa/skin.
  • Stages:
    • 1°: Painless chancre (infectious).
    • 2°: Systemic; rash (palms/soles), condyloma lata.
    • 3°: Gummas, CVS syphilis, neurosyphilis.
  • Congenital: Hutchinson's triad (notched incisors, keratitis, deafness).
  • Diagnosis: Dark-field (1°), VDRL/RPR (screen), FTA-ABS/TPPA (confirm).

• Gonorrhea (Neisseria gonorrhoeae - Gram-neg diplococci):

  • Morphology: Intracellular Gram-neg diplococci.
  • Pathogenesis: Pili attach to mucosa.
  • Clinical: Purulent urethritis/cervicitis; PID, Fitz-Hugh-Curtis. Ophthalmia neonatorum.
  • Diagnosis: Gram stain, Thayer-Martin, NAAT.
  • 📌 "Gonococci" = "coffee beans" shape.

• Chlamydia (Chlamydia trachomatis - obligate intracellular):

  • Life Cycle: Elementary Body (EB, infectious, 📌 "Enters"), Reticulate Body (RB, replicative, 📌 "Reproduces").
  • Serovars D-K: Urethritis, PID, neonatal conjunctivitis/pneumonia.
  • Serovars L1-L3: LGV (inguinal buboes).
  • Diagnosis: NAAT (gold standard).
  • Associated: Reiter's syndrome. ⭐ > Chlamydia trachomatis is the most common bacterial STI; often asymptomatic, leading to "silent" PID.

Viral Villains - Microscopic Menaces

• HPV (Human Papillomavirus)
  • Micro: Koilocytes (pathognomonic: perinuclear halo, “raisinoid” nucleus).

    ⭐ Koilocytes are pathognomonic for HPV infection, characterized by nuclear atypia and perinuclear vacuolization.

  • Oncogenic: Serotypes 16, 18 → SCC (cervix, anogenital, oropharynx) via E6 (↓p53), E7 (↓Rb).
  • Benign: Serotypes 6, 11 → Condyloma acuminata (anogenital warts).
• HSV (Herpes Simplex Virus)
  • Clinical: Painful grouped vesicles → ulcers (genital HSV-2 > HSV-1; oral HSV-1 > HSV-2).
  • Micro: Tzanck smear (multinucleated giant cells, Cowdry type A eosinophilic intranuclear inclusions).
  • Key: Lifelong latency in sensory ganglia (e.g. sacral); reactivation.
• HIV (Human Immunodeficiency Virus)
  • Genital: May cause ulcers; critically ↑ susceptibility & severity of other STIs (co-infections).
  • Mechanism: Progressive CD4+ T-cell depletion → immunosuppression (AIDS).
• HBV (Hepatitis B Virus)
  • Transmission: Sexual, parenteral (blood/needles), perinatal (vertical).
  • Risks: Chronic infection (~90% perinatal, <5-10% adult) → cirrhosis, Hepatocellular Carcinoma (HCC).

Other Pathogens & STI Syndromes - The Mixed Bag & Aftermath

• Trichomonas vaginalis:
  • Flagellated protozoan; pear-shaped, motile trophozoites on wet mount.
  • Causes vaginitis; "strawberry cervix" (colpitis macularis, punctate hemorrhages).
• Candidiasis (Vulvovaginal):
  • Candida albicans most common; see pseudohyphae & budding yeasts (KOH mount).
  • Predisposing factors: Diabetes, antibiotics, pregnancy, immunosuppression.
• Pelvic Inflammatory Disease (PID):
  • Polymicrobial ascending infection (key pathogens: N. gonorrhoeae, C. trachomatis).
  • Major sequelae: Infertility, ectopic pregnancy, chronic pelvic pain, tubo-ovarian abscess.
  • 

  • ⭐ Fitz-Hugh-Curtis syndrome (perihepatitis with "violin-string" adhesions between liver capsule and peritoneum) is a complication of PID.

• Syndromic Management (NACO guidelines):
  • Treats based on consistent groups of symptoms (syndromes), not etiology alone.
  • Uses pre-packaged, color-coded kits (e.g., Green kit for syndromic vaginal discharge).

High‑Yield Points - ⚡ Biggest Takeaways

• Syphilis (T. pallidum): Painless chancre (primary), condyloma lata (secondary), gummas (tertiary). Serology: VDRL/RPR, confirm with FTA-ABS.
• Gonorrhea (N. gonorrhoeae): Purulent discharge, PID. Microscopy shows Gram-negative diplococci in neutrophils.
• Chlamydia (C. trachomatis D-K): Often asymptomatic, major cause of PID. LGV (L1-L3 serovars) causes painful inguinal buboes.
• HPV: Koilocytes on Pap smear. Types 6, 11 cause condyloma acuminata; Types 16, 18 strongly linked to cervical cancer (via E6, E7 oncoproteins).
• HSV-2: Causes painful genital vesicles. Tzanck smear reveals multinucleated giant cells with intranuclear inclusions.
• Trichomoniasis (T. vaginalis): Profuse, frothy, greenish, foul-smelling discharge; characteristic strawberry cervix. Motile trophozoites on wet mount.
• HIV: Leads to AIDS, characterized by ↓CD4+ T-cell count, opportunistic infections, and specific malignancies like Kaposi's sarcoma.