Equis ISSN 2398-2977

Chlamydophila spp

Contributor(s): Christopher Brown, Susan Dawson




  • Order: Chlamydiales.
  • Family: Chlamydiaceae.
  • Genus:Chlamydia.
  • Species:psittaci,trachomatis,pneumoniae.


  • Gk:chlamys- a cloak.

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Clinical Effects



  • Respiratory, intestinal, and urogenital tracts of mammals and birds.


  • Elementary bodies enter cells by phagocytosis   →   reticulate bodies   →   binary fission   →   elementary bodies   →   released by cell lysis.
  • Cycle takes 30-40 hoursin vitro.


  • Inhalation or ingestion of infectious material, eg respiratory discharges and feces.
  • Vertical transmission via the egg occurs in some birds.

Pathological effects

  • Presenting condition and severity of disease related to immunologic status of the host animal.
  • Often partial immune response   →   chronic relapsing infection.
  • Ewes that have aborted, and recovered calves, appear to be resistant to reinfection.
  • Protective responses are cell-mediated.
  • Pathogenicity related to age, sex and health of host animal; route of infection; infective dose; strain and virulence of organism.
  • Birds:C. psittacicauses pneumonia, pericarditis, diarrhea, encephalitis, conjunctivitis.
  • Mammals:C. psittacicauses enzootic abortion of ewes, abortion of cows, genital infections, mastitis, intestinal infection and diarrhea, pneumonia, arthritis, encephalitis, conjunctivitis, hepatitis.
  • Cats: respiratory disease; mainly persistent conjunctivitis (C. psittaci).
  • Humans: pneumonia (C. trachomatis, C. pneumoniae), psittacosis/ornithosis (C. psittaci), abortion (C. trachomatis), conjunctivitis (C. trachomatis).
  • Horses: (mainlyC. psittaci) pneumonia, abortion   Abortion: overview  , conjunctivitis   Conjunctivitis: mycotic  , and urethritis .

Other Host Effects

  • The respiratory, genital and gastrointestinal tracts are the natural habitat in both mammals and birds.
  • Inapparent infections may occur with prolonged fecal shedding.
  • Psittacosis (infection due toC. psittaciin psittacine birds) and ornithosis (infection due toC. psittaciin non-psittacine birds) may result in a carrier state after recovery.
  • Stress may cause recurrence.


Control via chemotherapies

Control via environment

  • Zoonotic risk; pregnant women should avoid contact with lambing sheep.


  • Killed and live attenuated vaccines available for cats.
  • Live attenuated vaccines for sheep.


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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Mair T S & Wills J M (1992) Chlamydia psittaci infection in horses - results of a prevalence survey and experimental challenge. Vet Rec 130 (19), 417-419 PubMed.
  • Wills J M, Watson G, Lusher M et al (1990) Characterization of Chlamydia psittaci isolated from a horse. Vet Microbiol 24 (1), 11-19 PubMed.