THE first step towards implementing a control programme for EAE is the close monitoring of any abnormal signs during lambing time, according to Matt Haslam, an in-house vet with Benchmark Animal Health.

The disease, also known as chlamydial abortion, is the most common cause of abortion in the UK's sheep flock and is responsible for about half of all cases.

"Accurate record-keeping is very important, particularly on large units, where several people may be involved with the ewes at lambing time," said Mr Haslam.

"Details of any late-term abortions, stillbirths and weak lambs should be noted, along with ewes which fail to cleanse properly.

"I would suggest a maximum threshold figure of 5% for aborted lambs is applied, although 2% would be ideal. If numbers exceed this level, the farm vet should be contacted immediately, to conduct an investigation.

"There are a number of pathogens which cause abortion in ewes and it is crucial to know which one you are dealing with, to ensure treatment is successful. Two aborted lambs out of every 100 may be accepted as natural losses on farms with large flocks, but if EAE is the causal agent, the number of deaths will be much higher the following year," he argued.

Producers can help to increase the accuracy of diagnosis by retaining dead lambs and preserving samples of afterbirth from suspect ewes. Specimens should be stored in a clean container, before being sent to a laboratory for testing. However, individual vets vary and some may offer a diagnosis, after making a visual examination of infected material, he added.

EAE does not follow the same pattern as many of the other disease-causing pathogens: "A naïve ewe which is exposed to infection when she is less than 14 weeks in lamb will not be affected during her current pregnancy," he pointed out.

"The disease will lie dormant until the date of her next lambing approaches, when she is likely to suffer abortion and retained cleansing. In addition, infected ewes do not shed the harmful bacteria until two to three weeks prior to lambing and over the lambing period.

"The disease is transmitted when a naïve animal ingests EAE bacteria which are present in aborted lambs, infected placental material and vaginal discharge. Routine screening tests are not really applicable for EAE, and farmers frequently buy in diseased sheep which will appear normal."

The bacterium responsible for EAE causes inflammation of the placenta which, in turn, restricts the supply of nutrients and oxygen to the foetus. The disease is characterised by an inflamed placental membrane, which is reddish brown in colour and may appear thickened. By contrast, symptoms of abortion due to toxoplasmosis can cause the cotyledons linking the placental membrane to have a white, frosted appearance.

Ewes with EAE will usually exhibit the classic signs of abortion, unlike the mummified foetuses typically associated with toxoplasmosis.

A sharp increase in the number of lamb losses producers will experience, if their sheep become infected with EAE, is not the only way in which the disease affects farm profitability, Mr Haslam pointed out. A ewe which aborts her lamb will not cleanse effectively and has a high risk of uterine infection, which will reduce her future fertility.

There are a number of EAE vaccines on the market and, with one exception, these are live-attenuated versions and, therefore, restricted to when ewes are empty. As the only inactivated version of the vaccine, Benchmark's Mydiavac can be given to pregnant ewes. This means it can be used as a treatment in the event of an abortion storm.

"Swift action will raise the level of immunity of the flock and limit the damage caused by the disease not only at the current lambing, but also during the following year. After treatment, it will take about four weeks for the sheep to receive full protection against EAE.

Despite the complexities of the bacteria associated with EAE, flocks can be protected by routine vaccination of all replacements, and producers with an annual replacement rate of 25% can raise the health status of their flocks within four years.

He also advises anyone who regularly purchase replacements to limit purchases to vendors who vaccinate their sheep against EAE, or use Mydiavac after the tup has been removed.