Sexually Transmitted Diseases (STDs): Microbiology Study Notes

Sexually Transmitted Diseases (STDs)

Overview

Sexually transmitted diseases (STDs) are infections primarily spread through sexual contact. They can be caused by bacteria, viruses, or other microorganisms, and may affect various organ systems. Understanding the causative agents, symptoms, transmission, and prevention is essential for microbiology students.

Bacterial STDs

Gonorrhea

Gonorrhea is a common bacterial STD caused by Neisseria gonorrhoeae. It primarily affects the mucous membranes of the reproductive tract, but can also infect the rectum, throat, and eyes.

• Causative Agent: Neisseria gonorrhoeae (Gram-negative cocci, often diplococci)

• Symptoms:

  • Painful urination

  • Pus discharge (urethral, cervical, or rectal)

  • May be asymptomatic, especially in females

• Incubation Period: Usually 2–7 days after exposure

• Complications:

  • Can be passed to infants during vaginal delivery, leading to neonatal conjunctivitis (eye infection)

  • Pelvic inflammatory disease (PID) in women

• Transmission: Increasing in North America and other areas

• Treatment: Antibiotics (resistance is growing)

• Prevention: Safe sexual practices, regular screening

Example: Neonatal conjunctivitis is prevented by administering antibiotic eye drops to newborns.

Syphilis

Syphilis is a chronic bacterial STD caused by Treponema pallidum. It progresses through distinct clinical stages, each with characteristic symptoms.

• Causative Agent: Treponema pallidum (spirochete)

• Transmission: Direct contact with syphilitic sores during sexual activity

• Stages:

  • Primary Stage:

    • Painless sores (chancres) at site of infection

    • Typical sores resolve spontaneously after 3–4 weeks

  • Secondary Stage:

    • Occurs ~3 weeks after chancre resolution

    • Skin rashes on hands and soles of feet

    • Flu-like symptoms, mucous patches

  • Tertiary (Late) Stage:

    • Systemic infection affecting internal organs

    • Symptoms may appear years later

    • Can lead to organ failure and death

• Treatment: Antibiotics (penicillin is most effective)

• Prevention: Safe sexual practices, early diagnosis and treatment

Example: Early treatment of syphilis prevents progression to tertiary stage and severe complications.

Viral STDs

Herpes Simplex Virus (HSV)

Herpes Simplex Virus (HSV) is a viral STD that causes painful sores and blisters, primarily in the genital and oral regions. There are two main types: HSV-1 (commonly oral) and HSV-2 (commonly genital).

• Causative Agent: HSV-1 and HSV-2

• Characteristics:

  • Chronic infection; virus remains latent in nerve tissue

  • Recurring infections

• Symptoms:

  • Painful sores on the genitalia and surrounding skin

  • Symptoms appear shortly after infection and last 2–3 weeks

  • May be asymptomatic

• Transmission: Direct contact with infected skin or mucosa

• Pregnancy: Can be transmitted to infants during birth (especially with active lesions)

• Treatment: Antiviral medications help control outbreaks but do not cure infection

• Prevention: Safe sexual practices, avoiding contact during outbreaks

Example: Cesarean delivery is recommended for pregnant women with active genital herpes to prevent neonatal infection.

Human Papillomavirus (HPV)

Human Papillomavirus (HPV) is the most common STD in the U.S., affecting both men and women. It can cause genital warts and is associated with several cancers.

• Prevalence: ~20 million infected in the U.S.

• Symptoms:

  • Genital warts (may be internal or external)

  • Some infections are asymptomatic

• Transmission: Direct contact with infected skin or mucosa

• Cancer Connection:

  • Certain HPV types linked to cervical and penile cancers

  • High-risk types: HPV 16 and 18

• Vaccine: HPV vaccines protect against major cancer-causing strains

• Treatment: Topical medications and other dermatologic procedures

• Notes:

  • Infection may recur or appear with different HPV strains

  • Reinfection possible

Example: HPV vaccination is recommended for adolescents to prevent cervical cancer.

Comparison Table: Bacterial vs. Viral STDs

Feature	Bacterial STDs	Viral STDs
Causative Agents	Bacteria (e.g., Neisseria gonorrhoeae, Treponema pallidum)	Viruses (e.g., HSV, HPV)
Treatment	Antibiotics (curative)	Antivirals (control, not cure)
Prevention	Safe sex, screening	Safe sex, vaccination (HPV)
Complications	PID, infertility, neonatal infection	Cancer, chronic infection, neonatal infection

Key Terms

• STD: Sexually Transmitted Disease

• Incubation Period: Time between exposure and symptom onset

• Chancres: Painless sores characteristic of primary syphilis

• Latency: Period when virus remains dormant in host tissue

• Pelvic Inflammatory Disease (PID): Infection of female reproductive organs, often a complication of bacterial STDs