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Chlamydial (Enzootic) Abortion

Chlamydial abortion (also known as enzootic abortion of ewes (EAE), ovine enzootic abortion (OEA), or kebbing) is a major cause of lamb mortality across the world and the most common infectious cause of abortion in sheep and goats in the UK. It is caused by the bacteria Chlamydia abortus which invades the placenta during pregnancy which can lead to abortion or the birth of weak lambs.

Infection with C. abortus has both a direct and indirect effect on the developing lamb. Growth of the organism directly damages the placenta and the destructive effect of the inflammation its presence induces affects the transport of nutrients to the developing lamb and the production of the hormones which control pregnancy. In addition the organism may also cross the placenta and cause a degree of inflammation in the lamb’s internal organs.

Abortions due to C. abortus typically occur in the last few weeks of pregnancy. Work at Moredun has shown that regardless of when sheep become infected, the organism does not actively cause disease until after 80-90 days of pregnancy.

A high level of environmental contamination by infected ewes in lambing pens or fields is an important link in the spread of disease.  Infected lambs, placentas and excretions provide a source of infection to other susceptible ewes through ingestion and inhalation.

C. abortus is also a zoonotic pathogen and therefore can be passed from animals to humans posing a particular risk to pregnant women.  It is important that pregnant women and immune-compromised individuals should avoid contact with ewes during lambing time and should not handle contaminated clothing from those working with lambs.

Key Points

  • Enzootic abortion in sheep is caused by the bacterial pathogen Chlamydia abortus
  • The disease is variously known as Enzootic Abortion of Ewes (EAE), Ovine Enzootic Abortion (OEA), chlamydial abortion and ovine chlamydiosis
  • C. abortus has an affinity for the placenta (afterbirth) which is damaged by the invading pathogen and can lead to abortion or the birth of weak lambs
  • Aborted lambs, placentas and vaginal discharges from infected ewes are heavily contaminated with C. abortus and are a danger to other susceptible sheep and to pregnant women
  • Prompt isolation of aborted ewes, destruction of their placentas and dead lambs and disinfection of the abortion site are essential for limiting spread of infection
  • Ewes that have experienced enzootic abortion develop immunity to the disease which protects them from disease in subsequent pregnancies
  • Enzootic abortion may be prevented by vaccination and/or buying replacement stock from sources known to be free from EAE
  • Currently there are 3 vaccines (two live and one inactivated) available in the UK
  • Management practices to keep a flock “clean” can be supported by joining the Premium Sheep and Goat Health Scheme (EAE accreditation)
  • Oxytetracycline can be used to treat in-lamb ewes during an outbreak to reduce the number of abortions


Research at Moredun

Moredun has a major programme of research aimed towards understanding the pathogenesis of C. abortus in sheep and developing improved methods and strategies for the management, diagnosis and control of infection.

The aim of our research is a better understanding of the immunological mechanisms underlying disease pathogenesis as well as the identification and characterization of chlamydial components that interact with the host, with a view to the development of improved vaccines and diagnostic tools.

The development and commercialisation of a Chlamydia abortus diagnostic blood-test has been a major achievement. The test allows for accurate diagnosis of the disease by offering high specificity and sensitivity of detection.  The test detects the presence of antibodies to C. abortus in blood samples from infected sheep using an indirect ELISA technique.

Specific objectives include:

Research Funding

BMGF project, Supporting Evidence-Based Interventions (SEBI): Causes and extent of mortality of domestic ruminants in Tanzania.

Scientists at the Moredun Research Institute are working closely with colleagues at the University of Glasgow and colleagues from several organisations within Tanzania in order to determine the significance of Neospora caninum, Toxoplasma gondii and Chlamydia as infectious causes of abortion in sheep, cattle and goats in Tanzania.

A news release with further information about this project can be found here.


BBSRC project (BB/E018939/1), Conducting deep genome sequencing of C. abortus strains to investigate strain variation.

In collaboration with the Sanger Institute


BBSRC project (BB/E018939/1), Identification and characterization of chlamydial pathogenicity factors, such as those of the type V secretion system.

Funded through the Combating Endemic Diseases of Farmed Animal Species initiative.


BBSRC IPA project (BB/J015083/1), Studying the prevalence and pathogenesis of novel Chlamydia-related organisms in UK cattle.

Farming and Veterinary Outreach

Please see Moredun Newssheet 7.3 - Control of Enzootic Abortion in Sheep: