Enzootic abortion in sheep is caused by a bacterium called Chlamydophila abortus (former name Chlamydia psittaci). It is one of the most common causes of abortion in sheep (together with toxoplasmosis). It can also cause abortion in cattle and goats but more importantly it can cause abortion and illness in humans. An initial outbreak can lead up to 30% or more of ewes aborting(or giving birth to weak lambs) the following year, with the incidence remaining at 5-10% further lambing seasons, if left untreated. On a farm a 5% abortion rate can cause reduction of the potential gross margin by as much as 10%.

It can remain infective in the environment for several days in typical spring weather and for months if the temperature is freezing or near freezing. Chlamydia spp. and Chlamydophila spp. are susceptible to most disinfectants and detergents, they are resistant to acids and alkali.


This infection can be spread via:

  • Ingestion,
  • Aerosols,
  • Direct inoculation into the eye
  • On farmer’s clothing
  • Possibly venereal transmission (this is unlikely to contribute greatly)
  • Even via foxes or crows dragging infected placentae or fetus to neighbouring farms.

Some risk factors for sheep that primarily have an effect are:

  • The type of animal production
  • Proximity to other farming establishments
  • Animal replacement policy
  • Frequency of abortions
  • Undernourishment
  • Overpopulation
  • Transport
  • Sub-clinical bacterial and parasitic diseases.

On farm transmission can be summarized to possibly be via:

  • ewe-ewe contact,
  • aborted fetus contact,
  • contact with infected placental material,
  • via the vaginal discharge from aborted ewes,
  • from lambs in the first week of their life having survived an intra-uterine infection (experimentally it has been found that the fetus is not susceptible until the last 1/3 of gestation),
  • Infection of barren ewes or ewes in late pregnancy and via carrier ewes (asymptomatic carriers). In infected barren ewes or ewes in late pregnancy the infection remains sub-clinical until day 90 of the subsequent gestation when causative agentscan be detected in the placentae, and can persist up to 3 years.

Ewes who have aborted shed C. abortus from 1 day before, to 2-3 weeks after the abortion. These ewes who have previously aborted are immune, but as previously stated can continue to shed C. abortus. They are the asymptomatic carriers. It has been found that these carriers shed infection only during the periovulation period.


The development of clinical signals of chlamydiosis depends on the time period of infection.

  • Late term abortion, typically in the final 3 weeks of pregnancy.
  • Still births.
  • Birth of weak, low weight or premature offspring.
  • Reddish brown vaginal discharge for several days up to 3 weeks after the abortion.
  • Infected animals show no clinical illness prior to abortion, although behavioral changes and a vulval discharge may be observed in ewes within the last 48 hours of pregnancy. The ewe usually remains otherwise healthy and rarely has a retained placenta or a metritis.


The aim of the treatment is to kill C. abortus. when they are active during late pregnancy. During an outbreak it is possible to use an inactivated vaccine.

  • To reduce the severity of the infection and increase viability of lambs Alamycin LA (oxytetracycline 200mg/ml) at a dose rate of 20mg/kg body weight can be used. Ideally this should be administered between 95 and 100 days of gestation. A further treatment may be given 2-3 weeks later.

It is very advisable that when abortions occur the following management plan should be taken into account:

– Rapid removal and isolation of the aborting ewes and removal of all the products of abortion.

– Disinfection of the pens

– Very importantly personal hygiene (C. abortus can be transmitted via hands, clothing and even boots).


  • It is very advisable to cull all aborted ewes.
  • If at all possible the shepherd should try and keep his flock closed.
  • If replacements are needed, always buy them from green zones/disease free or accredited replacements.
  • If it is not possible to keep the herd closed, then another option could be to run a separate flock for the replacement ewes at lambing time. Again this is not always feasible.
  • There are also very effective vaccinations available to vaccinate the ewes up to 4 weeks before and after mating. Only replacements ewes would need to be vaccinated once the whole flock has been done.


As already stated C. abortus is a zoonosis meaning that it can be spread from animals to people too. The symptoms in humans are sometimes asymptomatic and other times the person can show flu like symptoms (fever, chills, headaches, dullness, muscular pain). Pregnant women are very susceptible to infection and abortion, especially at 24-36 weeks of pregnancy. Contamination can be via inhalation of aerosols and dust, but also a short stay in a room where infected animals have been! So please take care of yourself especially when expecting.



  • Mushi E.Z. Binta M.G. Chabo R.G. and Modisa L. (1999). Diseases of goats in Botswana. Government Printer, Gaborone. Botswana.ISBN-99912-1-331-7