Although this has not yet been published in a scientific journal we are excited to present to you the results of the Grass Sickness Vaccine trial where the full report has been made available on the Equine Grass Sickness Fund Website.
Can you vaccinate against Grass Sickness?
Equine grass sickness (EGS) is a devastating disease affecting grazing equids in many countries but is most prevalent in the UK, particularly on the east coast of Scotland. The disease is seen most frequently in young horses during the spring and summer months and is frequently fatal. The nerves of the gastrointestinal tract (gut) are damaged, causing difficulty swallowing and moving food through the gut. The cause of EGS is still unknown but multiple factors are likely to be involved. Evidence supporting the potential involvement of toxins from the bacterium Clostridium botulinum led to a nationwide field trial of a vaccine using an inactivated form of C. botulinum type C from 2014 to 2018, the results of which have recently been disseminated. The trial involved over 1,000 horses and ponies from 120 premises across the UK which had previously been affected by a high incidence of EGS. The study aimed to determine the effectiveness of the vaccine in preventing EGS, by comparing the incidence between groups of vaccinated and placebo-treated horses and ponies on each yard. Results showed that the vaccine used was safe, with a low frequency of local injection site reactions reported. Most equids vaccinated with C. botulinum type C had a significant immune response, in terms of raised antibodies, following the first vaccination course, whilst placebo treated equids showed little change in their antibody levels. Unfortunately, the incidence of EGS was considerably lower than anticipated, with just nine confirmed cases occurring amongst the enrolled horses and ponies over the entire trial period which meant that the study could not detect whether the vaccine was effective or not. Both young animal age and low C. botulinum type C antibody levels were significantly associated with an increased risk of EGS.
Dr. Richard Newton at the Animal Health Trust commented on the research: “Although the EGS field trial did not demonstrate a significant protective effect of the C. botulinum type C vaccine against EGS, this truly unique research has still achieved a number of things. We now have a greater understanding of equine grass sickness and the trial provided further evidence of vaccine safety under conditions of field use.”
For the full report on the vaccine trial please click here