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The importance of testing and vaccinating for enzootic abortion of ewes

EAE can be financially and reproductively devastating for farmers, so it is advisable that vets raise awareness of preventative measures before the disease gets into the flock

03 June 2021, at 9:00am

Enzootic abortion of ewes (EAE) is the most commonly diagnosed cause of abortion in UK sheep (APHA and SRUC, 2018), costing the UK sheep industry up to £20 million annually (Milne et al., 2009). The Q1 2020 APHA/SRUC Small Ruminant Quarterly Report for disease surveillance and emerging threats revealed that 42 percent of all diagnosed abortion cases during this period were attributed to EAE (177 out of 420 cases).

Over a 10-year period between 2009 and 2019, the APHA Surveillance Intelligence Unit found that 2,819 farms had repeat occurrences of EAE (Carson et al., 2019). Indeed, EAE was responsible for over 35 percent of all abortion diagnoses between 2012 and 2018 and 47 percent of all 2019 laboratory submissions. A review of case histories for a selection of farms with EAE incidents in four or more years, with the most recent diagnosis in the 2018/2019 lambing season, revealed that in one flock alone losses were as high as 26 percent (43 lambs dead in a flock of 160). The cost of a lamb lost during the neonatal period was as high as £25, and this does not include the potential earnings lost from lambs not going on to be raised and sold. In one flock assessed, neonatal losses accounted for at least £1,700. The absence of a vaccination programme was a consistent finding in the review.

Infection

Caused by Chlamydia abortus, bacteria are spread in aborted material and post-abortion vaginal discharges from ewes. They can survive for a few days in warm conditions and longer in cold conditions (Essig and Longbottom, 2015). Ewes are infected via the oronasal route, meaning that the bacteria can spread easily, as ewes tend to sniff around the area where another ewe has lambed after the event. Lambs fostered on to an aborted ewe can become infected by coming into contact with vaginal discharge on the udder and wool.

One of the main challenges with this disease is that the bacteria have the ability to lay latent in ewes until the next pregnancy. One infected sheep aborting and then shedding the bacteria has the potential to infect multiple ewes that will abort at their next lambing, potentially causing an abortion storm.

Diagnosis and testing

Obtaining an accurate diagnosis in cases of ovine abortion is key to putting future preventive plans in place. Investigation is recommended if 2 percent or more of a total flock have aborted or if two or more ewes have aborted over two to three days, irrespective of the size of the flock. However, any abortion should be investigated if the cause is not known, or if typical signs of EAE are noticed:

  • A rust-coloured vulval discharge which also covers the aborted foetus
  • A bright red aborted placenta
  • A ewe that is otherwise well

The ideal samples are freshly aborted foetuses and placentas which should be submitted for laboratory diagnosis. If a diagnosis is not possible during lambing, then some companies offer subsidised farm serology testing for Chlamydia abortus. Aborted ewes can be tested for Chlamydia abortus, ideally from three weeks to three months after lambing.

Control

Disinfection, isolation and investigative measures should be followed, as every abortion may be infectious. Advice for farmers with aborting ewes includes:

  • Use gloves and wash hands thoroughly after contact with an aborted ewe or contaminated material
  • Contact your vet if: 2 percent or more of your total flock have aborted; two or more ewes have aborted over two to three days, irrespective of the size of the flock; or if an abortion has occurred that fits the profile of EAE
  • Ideally, send the whole lamb foetus and placenta for testing. If this is not possible then arrange for your vet to take samples to send to the lab
  • If there are multiple lambs from the same ewe, send the freshest foetus and placenta
  • Make sure the sample is as fresh as possible as this will give the best results
  • When investigating an abortion outbreak, try to sample more than one ewe
  • Do not foster a lamb on to a ewe that has aborted
  • Clearly identify any ewes that have aborted if blood samples are needed and ensure that the mark will last until sampling/repeat after shearing. Ewes can be blood sampled up to three months after lambing
  • Isolate ewes for three weeks after an abortion as Chlamydia abortus can live in the environment for this period of time (Longbottom and Coulter, 2003)
  • Rapidly collect and destroy any bedding material that the ewe could have contaminated and thoroughly disinfect the area
  • Follow “hands, face, space” due to the zoonotic risk

Prevention

Vaccination

The Responsible Use of Medicines in Agriculture Alliance (RUMA) Targets Task Force Report 2017 commented that an unpublished survey undertaken in 2015 indicated that prophylactic use of antibiotics to manage EAE was routine for 10 percent of sheep farmers (RUMA, 2017). One of the aims of the task force is to increase the use of vaccines for EAE by 5 percent per year over the next five years, which will ensure the responsible use of antibiotics; however, during 2018 only 1 million of the 3.5 million replacement ewes in the national flock were vaccinated.

It is estimated that just one abortion caused by EAE could cost a farmer about £85 when taking into account: getting ewes in lamb, supporting the pregnancy, cleaning up after abortion, vet investigation, carcass disposal and veterinary costs to treat the ewe or purchase a replacement, without considering the loss of lamb sale (Scott, 2009). For a flock of 100 ewes this could lead to a loss of over £5,000 over a four-year period, while vaccinating a flock of 100 would cost approximately £300 in the first year and an estimated cost of £75 per year for replacements.

Ewes can be vaccinated for EAE from five months of age until four weeks prior to tupping, as long as the ewe is not in lamb.

Biosecurity

Bought-in ewes may already be vaccinated against EAE, but to protect a flock, replacement ewes should be housed and managed separately until after lambing. Biosecurity to prevent mixing with other flocks is essential and it is also worth considering whether any neighbouring farmers keep their flocks in adjoining fields.

Boot cleaning and disinfection facilities should be available to all, but particularly to any farm workers who work with other flocks who should also wear clean, separate overalls for each flock.