Update on Chlamydia Abortion of Ruminants

Dr Rick Last – Specialist Veterinary Pathologist

Vetdiagnostix – Veterinary Pathology Services


The previously revised classification system of the Family Chlamydiaceae (1990) separated the Genus into Chlamydia and Chlamydophila. In 2010 the taxonomists proposed that only a single Genus (Chlamydia) should be considered in the Family and so the Genus Chlamydophila has now fallen away.

Chlamydia abortion in domestic ruminants (cattle, sheep and goats) is now considered to involve two distinct syndromes namely

Enzootic abortion caused by Chlamydia abortus

Sporadic abortion caused by Chlamydia pecorum

Chlamydia abortus is a major cause of bacterial abortion in sheep and goats, and to a lesser extent in cattle worldwide. Previously, it was believed that all the chlamydial diseases in sheep and goats, including abortion, polyarthritis, and conjunctivitis, were caused by Chlamydia psittaci and that the organism could also be found in the intestines of sheep with no clinical signs of disease. Chlamydia abortus, previously Chlamydia psittaci immunotype / serovar 1, has now been shown to be a different and separate organism to Chlamydia psittaci. Enzootic Abortion frequently occurs as a reproductive flock / herd disorder in the absence of other so-called Chlamydia “syndromes”.

Chlamydia pecorum (also confirmed to be a different and separate organism to Chlamydia psittaci), has been associated with conjunctivitis, polyarthritis, gastroenteritis, mastitis and meningoencephalitis. Recent publications have now linked this bacterium to sporadic abortion in domestic ruminants associated with fetal hepatitis and enteritis plus necrotizing fibrinopurulent placentitis with vasculitis.

Important Chlamydia species of ruminants

  • Chlamydia abortus – Enzootic Abortion (Ovine Chlamydial Abortion, Ovine Chlamydiosis).
  • Chlamydia pecorum – Sporadic abortion, polyarthritis, conjunctivitis, pneumonia, metritis, encephalomyelitis and subclinical enteric infections.
  • Chlamydia psittaci – rarely associated with pneumonia, but usually in conjunction with other respiratory pathogens. Not considered a primary lung pathogen of sheep or goats.


Confirmatory Tests

  • Impression smears of placenta and abomasal fluid smears for Gimenez stains.
  • Placenta, lung, liver impression smears for C. abortus + C. pecorum PCR.
  • Placenta (cotyledonary and inter-cotyledonary), liver, spleen, lymphnodes, lung and brain in 10% buffered formalin for histopathology.
  • IHC staining for Chlamydia antigen on formalin fixed tissues.

Chlamydia ELISA antibody serology is mostly applicable as a screening test to establish a baseline indication of infection in a flock / herd with unknown Chlamydia vaccination status or history. From this one can establish whether Chlamydia needs to be further investigated as regards perceived flock problems, plus one could estimate the risk of possible epizootic outbreaks in these flocks. In unvaccinated flocks / herds one can use it as a tool to make relevant decisions about introduction of a routine vaccination program.

There is limited application for antibody serology in vaccinated flocks, other than for acute and convalescent serology during abortion outbreaks to be used in conjunction with pathology and PCR.

The role of Chlamydia in reproductive issues in African Wildlife, in particular African Buffalo and various antelope species, is unknown at this stage.


  1. Buxton D et al. 2002. Ovine chlamydial abortion: Characterization of the inflammatory immune response in placental tissues. Journal of Comparative Pathology 127:133-141.
  2. Entrician G et al. 2001. Chlamydial infection in sheep: immune control versus fetal pathology. Journal of the Royal Society of Medicine. 94:273-277.
  3. Giannitti et al. 2016. Chlamydia pecorum: fetal and placental lesions in sporadic caprine abortion. Journal of Veterinary Diagnostic Investigation 28:184-189.
  4. Njaa B L. 2012. Diagnosis of abortion and neonatal loss in animals. 4th edn. Wiley-Blackwell.
  5. OIE Terrestrial Manual 2012. Enzootic Abortion of Ewes.
  6. Papp et al. 1993. Chlamydia psittaci infection and associated infertility in sheep. Canadian Journal of Veterinary Research. 57:185-189

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