• Clinical science

Chlamydia infections

Abstract

Chlamydiaceae is a family of gram-negative, obligate intracellular bacteria that includes 3 organisms pathogenic to humans: Chlamydia trachomatis, Chlamydophila pneumoniae, and Chlamydophila psittaci. C. trachomatis can be differentiated into serotypes A–C, D–K (the most common STI), and L1–L3. Serotypes A–C mainly affect the eyes and cause trachoma. An infection with serotypes D–K can result in genitourinary infections (e.g., vaginitis, PID, urethritis), conjunctivitis, and infant pneumonia. Serotypes L1–L3, in turn, lead to sexually transmitted lymphogranuloma venereum. While both C. pneumoniae and C. psittaci primarily affect the respiratory system, C. psittaci also causes psittacosis. Chlamydial infections are mostly diagnosed based on clinical presentation and are treated with doxycycline or macrolides. In all cases of sexually transmitted chlamydial infection, expedited partner therapy should also be initiated as soon as possible. All ocular manifestations are discussed in more detail in the conjunctivitis learning card.

General

  • Bacteria characteristics
    • Gram-negative bacterium, but does not gram stain well because:
    • Characteristic life cycle consisting of two phases
      • First phase: elementary bodies
        1. Attachment of extracellular elementary bodies to target cells (mostly on the respiratory or urogenital epithelium)
        2. Endocytosis
        3. Transformation into reticulate bodies in the endosome
      • Second phase: reticulate bodies
        1. Multiplication and aggregation of various reticulate bodies in the endosome, which take over most of the infected cell, at which point they are called inclusion bodies. Inclusion bodies are visible under light microscopy.
        2. Transformation of reticulate bodies to elementary bodies
        3. Lysis of endosomes
        4. Release of newly formed elementary bodies and exit from cell
        5. New start of cycle
    • Cultivation very difficult
  • Features
Bacteria Serotypes Organ Transmission Disease
Chlamydia trachomatis A–C
  • Eyes
  • Smear infection via discharge from the eyes or nose of infected persons
  • Can be transmitted by direct contact, clothes, or insects.
D–K
  • Eyes
  • Genitourinary tract
  • Lungs
  • Sexual intercourse
  • Vaginal birth (in which the mother is infected)
L1–L3
  • Urinary tract
  • Anorectal area
  • Genitourinary tract
  • Sexual intercourse
Chlamydophila pneumoniae
  • Person-to-person transmission of respiratory secretions
  • Infection of the respiratory system → atypical pneumonia, especially in the elderly[3]
Chlamydophila psittaci
  • Airborne transmission (pathogens in the feces and dander of birds)

Chlamydial pneumoniae

Sexually transmitted infections

Chlamydial genitourinary infections

Lymphogranuloma venereum

Lymphogranuloma venereum (LVG) causes painless genital ulcers, which heal spontaneously within a few days. After a few weeks, swelling of the lymph nodes occurs, with possible abscess formation and discharge of pus. Without antibiotic treatment, this can lead to chronic lymphedema. (Also see the learning card on sexually transmitted infections)

  • Pathogen: Chlamydia trachomatis serotypes L1–L3
  • Epidemiology
    • Found mostly in tropical and subtropical countries
    • Increasing incidence among MSMs
  • Clinical features
    • Primary infection after about a week: painless, herpetiform ulcers
    • Secondary infection after about three weeks: painful lymph nodes in the inguinal region (buboes); with formation of abscesses (pus); , systemic symptoms
  • Treatment: doxycycline; alternatively, erythromycin
  • Complications

[20]

Lymphogranuloma venereum (pathogen: Chlamydia trachomatis serotypes L1–L3) should not be mistaken for granuloma inguinale or donovanosis (pathogen: Klebsiella granulomatis)!