Sexually Transmitted Infections Lecture Notes

The genital tract is essential for reproduction, which is vital for life.
Estimated 1 million STDs are contracted each day globally.
Over 30 diseases are recognized to spread primarily through sexual activity.
Source: Division of STD Prevention, National Center for HIV, Viral Hepatitis, STD, and TB Prevention, Centers for Disease Control and Prevention (CDC).

STDs/STIs are microorganisms shed from the urogenital tract and transmitted through mucosal contact with susceptible individuals during sexual activity.

Discharge: Some microorganisms (e.g., Gonorrhea, Chlamydia) are efficiently transmitted through discharge when they are carried over epithelial surfaces.
Sores/Ulcers/Warts: Effective transmission occurs from sores or areas of infection.
Semen: Many microorganisms (e.g., viruses) can be spread via semen.
Horizontal Transmission: No known animal vector exists for the microorganisms causing STIs.

Formula: R_0 = eta DC
- R_0: Basic reproduction number – the number of cases one case generates during its infectious period.
- eta: Efficiency of transmission (expressed as a probability).
- D: Duration of infectivity.
- C: Number of individuals exposed (sexual partners).

Frequency of sexual encounters: Increased population density, mobility of individuals, and the rise of social media/dating apps.
Use of contraceptives: Notably, decreased usage among young populations.
Transmissibility Efficiency: Comparative transmissibility of sexual practices: Anal > Vaginal > Oral.
High-Risk Groups: Higher risks are noted among women, men who have sex with men (MSM), particularly MSM of color and transgender women of color, and individuals with substance abuse problems.

STDs more prevalent in rural areas and among those in poverty, without health insurance, or experiencing housing instability.

Bacterial: e.g., Chlamydia trachomatis, Mycoplasma genitalium.
Viral: e.g., Herpes Simplex Virus (HSV), Human Papillomavirus (HPV), Human Immunodeficiency Virus (HIV).
Protozoan: e.g., Trichomonas vaginalis.
Arthropod: e.g., Pubic lice, scabies.

Mucopurulent Cervicitis/Vaginitis and Urethritis: Presence of mucus and pus discharge from the cervix, vagina (women) or urethra (men). Common in gonorrhea and chlamydial infections.
Genital Ulcer Disease: Characterized by open sores on the genital area such as the vulva, penis, perianal region, or anus, commonly seen in syphilis, chancroid, and genital herpes.

Asymptomatic: Transmission is prevalent even when asymptomatic, highlighting the necessity for screening at-risk individuals.
Local Infection: Results in symptoms localized to the genitourinary area, including lesions and pelvic inflammatory disease.
Systemic Infection: Primarily seen in cases such as HIV or secondary syphilis.

Fallopian Tube Damage: Scarring and adhesions can lead to ectopic pregnancy, infertility, and chronic pelvic pain.
Congenital Diseases: Birth defects linked to infections like syphilis, herpes, papillomatosis, and chlamydia.
Increased HIV Risk: Presence of genital ulcers or altered mucosa heightens the likelihood of HIV acquisition.
Pregnancy Outcomes: Serious complications include premature termination, fetal wastage, low birth weight, and premature rupture of membranes.

Pelvic Inflammatory Disease (PID): An infection affecting the uterus and fallopian tubes, primarily caused by Gonococci and Chlamydia.
Anogenital Cancer: Development of cancers such as cervical cancer, associated with certain HPV types.
Recurrent Herpes Infections: Significant health implications related to viral persistence in the host.

Generally not well characterized.
The upper genital tract is typically sterile while the lower tract (urethra and coronal sulcus) may be colonized.
Microbiota influenced by sexual activity and circumcision, with specific species linked to bacterial vaginosis (e.g., Prevotella, Atopobium, Megasphaera, Gemella).

Components: Mucus, secretory Immunoglobulin A (sIgA), Immunoglobulin G (IgG), antimicrobial peptides, innate immune cells, and adaptive immune cells (largely memory cells).

Semen contains elements with antimicrobial properties, including:
- Zinc, lysozyme, transferrin.
- Antimicrobial peptides: $eta$-defensins, human epididymis peptide 2, hCAP-19, PIF, epididymal protease inhibitor, semenogelins, and surfactant protein D.

The testis is considered an immune privileged site due to:
- Interstitial tissues hosting blood vessels, lymphatics, and mast cells.
- Tight junctions in Sertoli cells preventing the entry of antibodies, complement, and immune cells into the seminiferous tubules.
- Sertoli cells secrete substances that promote immune suppression including FasL, IDO1, and TGF-β.

The integrity of the blood-testis barrier is maintained through the tight junctions between Sertoli cells which effectively exclude antibodies and immune cells from seminiferous tubules.