Microbial Pathogens: Chlamydia trachomatis, Herpes Simplex Viruses, and Human Papillomavirus

Chlamydia trachomatis

Overview and Strains

Chlamydia trachomatis is an obligate intracellular bacterium that infects humans and is a major cause of sexually transmitted and ocular diseases worldwide.

• Human reservoir: Humans are the only known reservoir for C. trachomatis.

• Trachoma strain: Attacks mucous membranes of the eyes, genitourinary tract, and lungs.

• Lymphogranuloma venereum (LGV) strain: Invades lymphatic tissues of the genitalia, causing more severe disease.

Chlamydial Diseases of the Eye

Chlamydia trachomatis is responsible for several ocular diseases, which can lead to significant morbidity.

• Ocular trachoma: Severe infection that deforms the eyelid and cornea, potentially causing blindness. It is the leading infectious cause of blindness worldwide.

• Inclusion conjunctivitis: Occurs in newborns as they pass through the birth canal of infected mothers. Prevention includes prophylactic administration of erythromycin or doxycycline.

Sexually Transmitted Chlamydial Diseases

Chlamydia trachomatis is the most prevalent sexually transmitted organism, often causing asymptomatic infections and long-term reproductive damage.

• Chlamydiosis: Most common sexually transmitted infection (STI). Asymptomatic in 70% of women and 10% of men, leading to underdiagnosis and untreated cases.

• Nongonococcal urethritis (NGU): Inflammation of the urethra in males, mimics symptoms of gonorrhea.

• Pelvic inflammatory disease (PID): In women, can result from untreated chlamydial infection, leading to infertility and chronic pain.

• Lymphogranuloma venereum (LGV): Disfiguring disease affecting external genitalia and pelvic lymphatics.

Identification of Chlamydiosis

Accurate diagnosis is essential for effective treatment and control of chlamydial infections.

• Sampling: Requires dislodging cells from the mucosal surface for laboratory analysis.

• Immunofluorescence and PCR-based tests: Highly sensitive and specific methods for detecting chlamydial DNA or antigens.

• Giemsa or iodine stains: Useful for diagnosing inclusion conjunctivitis by visualizing intracellular inclusions.

• Limitations: Staining methods are not recommended for urogenital specimens due to low sensitivity and high false-negative rates, especially in asymptomatic patients.

Treatment

• Antibiotics: Doxycycline and azithromycin are the drugs of choice for treating chlamydial infections.

Cells of Chlamydia trachomatis

Microscopic examination reveals C. trachomatis cells attached to the microvilli of fallopian tubes, contributing to tissue damage and disease.

• Cell morphology: Small, round, intracellular bacteria visible in stained tissue samples.

• Pathology: Damaged fallopian tubes may contain numerous chlamydial cells, leading to infertility.

Herpes Simplex Viruses (HSV)

Overview

Herpes simplex viruses are enveloped DNA viruses that cause lifelong infections in humans.

• HSV-1: Primarily causes cold sores and fever blisters; usually acquired in early childhood.

• HSV-2: Causes lesions on the genitalia and possibly oral lesions; typically acquired in adolescence and adulthood (ages 14-29).

Epidemiology of Herpes Simplex

• Transmission: Direct contact with secretions containing the virus. Active lesions are the most significant source, but genital herpes can be transmitted even in the absence of visible lesions.

• Recurrent infections: HSV establishes latency in nerve cells, leading to periodic reactivation and recurrent symptoms.

Herpes of the Newborn

Neonatal herpes is a potentially fatal infection acquired before or during birth.

• Transmission: Infant may be contaminated by the mother before or during birth, or by hand transmission.

• Sites of infection: Mouth, skin, eyes, and central nervous system (CNS).

• Prevention: Screening pregnant women and delivery by C-section if an outbreak is present at the time of birth.

Diagnosis, Treatment, and Control of Herpes Simplex

• Diagnosis:

  • Vesicles and exudate are typical diagnostic symptoms.

  • Scrapings from the base of lesions may show giant cells (multinucleated cells).

  • Culture and specific tests, such as direct fluorescent antibody tests, are used for severe or disseminated HSV.

• Treatment:

  • Antiviral medications: acyclovir, famciclovir, valacyclovir.

  • Topical medications may be used for mild cases.

Human Papillomavirus (HPV)

Overview

HPV is a non-enveloped double-stranded DNA virus responsible for warts and several cancers.

• Papilloma: Refers to a wart or verruca caused by HPV infection.

• Strains: Over 100 different strains of HPV exist, with varying pathogenicity.

• Transmission: Direct contact or contaminated fomites; incubation period ranges from 2 weeks to over a year.

• Natural history: Most common warts regress over time but can be removed if necessary.

HPV and Cancer Risk

• Oncogenic strains: 14 HPV types are associated with an increased risk of developing reproductive cancers, especially cervical cancer.

• Screening: Early detection through inspection of genitalia and Pap smear screening for abnormal cervical cells in women.

• Prevention: Approved vaccine (Gardasil 9) protects against the most common oncogenic HPV types.

Summary Table: Key Features of Chlamydia trachomatis, HSV, and HPV

Pathogen	Type	Main Diseases	Transmission	Diagnosis	Treatment/Prevention
Chlamydia trachomatis	Bacterium	Trachoma, NGU, PID, LGV	Sexual, perinatal, direct contact	PCR, immunofluorescence, stains	Doxycycline, azithromycin
Herpes Simplex Virus (HSV-1, HSV-2)	Enveloped DNA virus	Cold sores, genital herpes, neonatal herpes	Direct contact with secretions	Clinical, culture, DFA	Acyclovir, C-section for neonates
Human Papillomavirus (HPV)	Non-enveloped dsDNA virus	Warts, cervical cancer	Direct contact, fomites	Pap smear, inspection	Gardasil vaccine

Additional info: The notes have been expanded to include definitions, clinical relevance, and prevention strategies for each pathogen, as well as a summary table for comparison.