As the high risk season for Equine Grass Sickness fast approaches the Animal Health Trust, one of the UK’s leading veterinary charities, is urging horse owners to take part in the second year of its ground-breaking nationwide EGS vaccine trial.

A debilitating and often fatal disease affecting horses, ponies and donkeys, Equine Grass Sickness (EGS) occurs predominantly in Europe, with Britain experiencing the highest incidence worldwide. In 2014, 59 cases of EGS were reported through the EGS Surveillance Scheme, but it is likely that this represents only a fraction of cases occurring annually throughout Britain.

Almost all cases of EGS occur in horses with access to grazing. Growing scientific evidence suggests that the disease may be caused by the bacterium Clostridium botulinum type C, commonly found within soil and capable of producing neurotoxins to which horses are particularly sensitive. EGS occurs when a combination of risk factors trigger the production of these toxins within the horse’s intestinal tract, causing damage to the nervous system and paralysis of the gut.

As similar equine diseases such as tetanus and botulism can be prevented by vaccination, it is theoretically possible that a vaccine could prevent EGS. To this end the Animal Health Trust, in collaboration with the Universities of Edinburgh, Liverpool and Surrey launched the EGS field vaccine trial in 2014 in order to establish whether a vaccine could indeed be effective in reducing the risk of the disease. The trial is generously funded by a number of sources including Neogen Corporation; Animal Welfare Foundation; Horserace Betting Levy Board; Racing Foundation; Moredun Foundation Equine Grass Sickness Fund; Hong Kong Jockey Club; The British Horse Society and the EB Moller Charitable Trust.

Now entering its second year, the EGS vaccine trial involves enrolled horses and ponies receiving either a course of the C. botulinum type C toxoid vaccine or an inactive placebo, as well as an annual booster. The incidence of EGS is monitored throughout the trial to determine the efficacy of the vaccine, and enrolled horses and ponies are closely monitored through regular follow-ups for the duration of the trial.

With 60% of EGS cases occurring during April – June, the highest risk season for EGS is fast approaching. The Animal Health Trust is appealing to owners who keep their horses on premises that have had at least one case of EGS in the past three years to enrol their horse in the vaccine trial and provide an invaluable contribution to this pioneering research prior to these high risk months.

Dr Jo Ireland, the AHT’s Equine Grass Sickness Research Co-ordinator, said, “We have been delighted with the overwhelmingly positive response to the EGS vaccine trial and many owners have welcomed the chance to be a part of such important research. We don’t want any eligible horse owners to miss out on the opportunity to contribute towards a potential breakthrough in the prevention of EGS, so we are encouraging more owners to enrol their horses on the trial this year.”

To find out more about the vaccine trial or how to enrol horses and ponies, please visit the AHT’s dedicated EGS website or email