Control of Chlamydial (Enzootic) and Toxoplasma Abortion in Sheep

Moredun-logoSummary written by Elisabeth Innes BSc PhD and Nick Wheelhouse BSc PhD

Taken from Moredun Foundation Newsheet Volume 5 No. 8



  • lambing-3-newborn-lambAbortion in sheep is usually due to an infection. Many of these infections are a special danger to pregnant women and some other groups of people.
  • Of the several different infections that cause abortion in sheep chlamydial (enzootic) abortion and toxoplasma abortion are the most common.
  • Correct management of abortion in the flock can reduce the risk of future trouble.

Chlamydial Abortion of Ewes

  • Chlamydial abortion of sheep, also known as enzootic abortion of ewes (EAE) or ovine enzootic abortion (OEA), is caused by a bacterium called Chlamydophila abortus (old name Chlamydia psittaci).
  • C.abortus can spread to the womb and placenta (afterbirth) of a sheep that is unprotected and kill the developing lambs
  • Aborted lambs and placentas from infected ewes are heavily contaminated with C.abortus and are a danger to other sheep and to humans.
  • There are 2 vaccines available in the UK: Enzovax®, (Intervet Schering Plough Animal Health), and CEVAC Chlamydia® (CEVA Animal Health Ltd)
  • Management practices to keep a “clean” flock can be supported by joining the Premium Health Scheme (EAE) run by SAC Veterinary Services or the Highlands and Islands Sheep Health Scheme which is jointly organized by HISHA and SAC Veterinary Services.
  • Oxytetracycline can be used to treat in-lamb ewes during an outbreak to reduce the number of abortions.


  • Toxoplasma gondiiis the most successful parasite worldwide, capable of infecting all warm blooded animals including humans. The cat and members of the cat family are definitive hosts of the parasite and infected cats can shed Toxoplasma oocysts (eggs) in their faeces.
  • Toxoplasma oocysts have a tough outer shell and can survive in the environment in moist temperate conditions for 12-18 months.
  • Sheep may become infected from ingesting infective oocysts on pasture or in contaminated feed and water. Once ingested the parasite multiplies within the animal and persists within tissue cysts in brain, heart and muscle.
  • In pregnant sheep if the parasite infects the animal for the first time, Toxoplasma can cause disease in the placenta and the developing foetus. Infection of sheep early in pregnancy may result in abortion, whereas infection later in pregnancy may cause still birth, mummified foetus or birth of a live but weak lamb.
  • Following infection sheep develop immunity against the parasite which will protect them against disease in a subsequent pregnancy.
  • There is an effective vaccine to prevent congenital toxoplasmosis in sheep (Toxovax® produced by Intervet Schering Plough Animal Health), which should be administered 3 weeks prior to mating.
  • Toxoplasma may also be transmitted to humans from the ingestion of oocysts or from eating undercooked meat containing parasite tissue cysts. Pregnant women and immuno-compromised individuals are major risk groups and should also avoid contact with ewes at lambing time.



sheep cover2 smMore information on managing your flock can be found on the DVD 'Managing Your Flock for Peak Health' - programme 2 in the series 'Sheep on Your Smallholding'.








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