CASE NOTES
Chlamydial abortion, Chlamydophila abortus, enzootic abortion of ewes (EAE)
Phil Scott DVM&S BVM&S CertCHP DSHP DipECBHM FRCVS
Reviewed: August 2016
Published: 2009
Posted Flock & Herd March 2025
Accessed from the National Animal disease Information Service www.nadis.org.uk 16 December 2024
INTRODUCTION
Infectious causes of abortion are most common after day 100 of pregnancy. While sporadic losses are variably attributed to handling procedures or movement, an abortion rate in excess of two per cent is suggestive of an infectious cause and veterinary investigation is essential at an early stage. Enzootic abortion of ewes, Toxoplasma gondii and Campylobacter species cause over 80 per cent of abortion outbreaks in the UK. The cost of abortion is variably quoted as £85 per aborted ewe.
ZOONOTIC RISK
Pregnant women are at serious risk from C abortus infection (zoonotic infection). Despite the availability of a highly efficacious vaccine, EAE is still the main cause of ovine abortion in the UK. Disease is acquired from exposure of susceptible sheep to high levels of infected uterine discharges and aborted material. Infection does not result in abortion during that pregnancy unless the ewe is more than six weeks from her due lambing date rather infection remains latent in the sheep until the subsequent pregnancy then causes abortion.
CLINICAL FINDINGS
Infection typically results in the abortion/birth of fresh dead and/or weak lambs during the last three weeks of gestation. The ewe is not sick and may only be identified by a red/brown vulval discharge staining the wool around the tail/perineum, and a drawn-up abdomen. Live lambs rarely survive more than a few hours despite supportive care.
Whole flock long-acting oxytetracycline injection (20 mg/kg) is an emergency measure that may reduce the number of abortions from C abortus infection, but such treatment cannot reverse placental damage with the result that lambs are carried closer to term but remain weak at birth with consequent high mortality. Antibiotic use in agriculture is coming under intense scrutiny and whole group injection can only be justified as an emergency measure then vaccination must be adopted.
MANAGEMENT
In common with all infectious causes of abortion, aborted ewes must be isolated and aborted material and infected bedding removed and destroyed. Ewes that give birth to dead/weak full-term lambs should also be isolated. Lambs fostered on to aborted ewes should not be retained for future breeding.
Freedom from C abortus infection is best achieved by maintaining a closed clean flock with strict biosecurity measures although there have been rare situations where infected material has been transmitted between neighbouring farms by birds/foxes.
Various accreditation schemes are operating which offer breeding female replacements from flocks monitored free of C abortus infection.
Vaccination offers an excellent means of control for farms buying breeding replacements from non-accredited sources, and in those flocks with an endemic C abortus problem. Vaccination of sheep already infected with C abortus will not prevent all abortions but can reduce the incidence.
The 'gold standard' would be to purchase accredited stock and vaccinate them against C abortus. Vaccination against C abortus costs £2-3 per dose but this cost must be divided over the ewe's productive life (three pregnancies at least). The cost of abortion is variably quoted £85 per aborted ewe.