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Chlamydia infections

Last updated: October 5, 2020

Summarytoggle arrow icon

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, 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” article.

General characteristics

Life cycle

  • First phase: elementary bodies (small and dense bodies that characterize the infectious stage of Chlamydiaceae; stable in the extracellular environment and almost inactive metabolically) [1]
    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 (represent the obligate intracellular, replicative, and metabolically active form of Chlamydiaceae)
    1. Replication by fission and aggregation of various reticulate bodies in the endosome (at which point they are called inclusion bodies)
    2. Transformation of reticulate bodies into elementary bodies
    3. Lysis of endosomes
    4. Release of newly formed elementary bodies and exit from cell
    5. New start of cycle

Elementary bodies survive in the Environment, Enter the cell via Endocytosis, and Evolve into reticulate bodies.

Reticulate bodies Replicate in the cell and Reorganize to elementary bodies.

Features

Characteristics of Chlamydiaceae
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
  • Sexual intercourse
Chlamydophila pneumoniae
  • Person-to-person transmission of respiratory secretions via aerosols
Chlamydophila psittaci
  • Airborne transmission (pathogens in the feces and dander of birds)

Infant pneumonia due to Chlamydia trachomatis (serotypes D–K)

Chlamydophila pneumoniae

Chlamydophila psittaci (psittacosis , "parrot fever" , or ornithosis ) [11]

Chlamydophila psittaci accumulates in parrots and other birds and causes atypical pneumonia.

Psittacosis is a notifiable disease and should be reported in most of the states.

Chlamydial genitourinary infections

Lymphogranuloma venereum [22]

C. trachomatis serotypes L1-L3 cause Lymphogranuloma venerum.

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

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