Recently doubt has been cast over the validity of the ‘Strangles Blood Test’ for identifying carriers coming onto yards. Increasingly yards are asking for testing of Guttural Pouch Lavage samples which owners regard as more invasive and are still not infallible. Either way these tests do not negate the risk of an outbreak entirely, particularly if the yard is not completely closed.
An adjunctive or alternative approach would be to vaccinate against the disease. Like Covid, when individuals are vaccinated, it gives us the confidence that the risk of getting a nasty form of the disease is reduced significantly.
A relatively new intramuscular vaccine provides immunity against the Strep equi bacteria that we associate with the disease known as Strangles.
Vaccines are useful at providing immunity against a particular disease so that when we are exposed to it, the body already has a degree of protection. The vaccine cannot give a 100% guarantee that your horse will not become infected, however, within a yard outbreak the protection means that for the majority of horses exposed to the disease we would expect to see minimal clinical symptoms. Some horses may still develop symptoms and spread the disease, although this would be at a significantly reduced severity.
The licensed protocol for the vaccine is to give a primary course of two vaccine doses at 4 weeks apart. The onset of immunity is considered to be 2 weeks after the second vaccination dose. In high-risk situations it is suggested to repeat this regime every 2 months.
However, there is now good clinical trial and field data particularly from its use on yards in Europe, on which we can base our decisions for moderate to low-risk situations. Vets will be using different protocols for this, and, like the Covid vaccines, we have to implement a workable and pragmatic protocol utilising the available science and license information. We are advising a primary course, described below, to hit the right balance between clinical efficacy, side effects and practical issues. As we gain more data this protocol may change and as this is not written into the license of the product, it’s use is considered ‘off-license’. Off license use is common for many of the products we use in equine veterinary practice.
Our proposed regime is to follow a similar programme as the Flu vaccinations with a primary course of two vaccine doses at 4 weeks apart. Then a first booster at 4 – 6 months followed by annual booster vaccinations in low-risk situations and every 6 months in moderate risk situations. Booster vaccinations which run over by more than a month should re-start the primary course.
In both moderate and low risk scenarios we would strongly advise re-vaccinating horses that have not had a vaccine within 2 months of become high risk i.e. where there is known/suspected strangles on a yard or within a close vicinity.
This is not a live vaccine so there is no risk of your horse getting Strangles from the vaccine. It will not interfere with interpretation of the strangles blood ELISA test. i.e. it will not raise the levels the labs look at to demonstrate exposure. It will also not interfere with the validity of the results of a PCR from a guttural pouch lavage.
Mild vaccination reactions are more common than horse owners would expect compared to our influenza vaccinations and can include a transient raised temperature, ocular discharge and lethargy. Local reactions at the injection site including heat, pain and swelling are very common and can be worse at subsequent injections. In our experience these have largely resolved without requiring any treatment. At Equitait we used the vaccine on our own horses and then monitored them closely for reactions the results of which are published on our website. The vets at Equitait continue to vaccinate their own horses.
Vaccination should not replace good biosecurity measures as these are still important in preventing Strangles and other infectious diseases. In a gold standard situation starting vaccination at or before the time of a guttural pouch lavage would mean it was starting from a known strangles status.
No information is available on the safety and efficacy of this vaccine when used with any other veterinary medicinal product. In our experience we have widely used it at the same time as other vaccines without issue, although we try to give them at different sites.
True herd immunity is only achieved when a large proportion of the same yard are vaccinated, and this is obviously preferable. However, even if your horse is the only one vaccinated on the yard it is still beneficial, and you can be confident that you are adding to your protection from those around you.
For yard managers, we feel that integrating vaccination into your biosecurity measures would result in a reduce risk in all yards. Many vets now believe that vaccination gives better protection to an established herd than pre-movement serology (bloods).
Insurance companies report that on average a case of strangles in a single horse will cost in excess of £1000. Where businesses are involved the loss of earnings can be considerably more and those who have seen nasty clinical cases will vouch for just how distressing it can be for both the animal and the owner.
If you would like more information or would like to discuss how you could implement vaccination to benefit your horse or yard in your specific situation then please call or e-mail the practice.
For further reading the article “Strangles vaccination: A current European perspective” gives a good overview of where we are now.
