XL Equine Vet Imogen Burrows discusses one of the most common equine infectious diseases.

Imogen BurrowsBVetMed CertAVP(EM) MRCVS RCVS Advanced Veterinary Practitioner in Equine Medicine

Part of the daily role is providing advice to clients on the end of the phone or by email where I can. This is particularly useful for owners in many circumstances, e.g. out of hours when deciding whether a visit is necessary, or for general advice on infectious diseases. Today it is the latter which is occupying a significant proportion of the time in my day.

One of the commonest infectious diseases that we are asked to talk to clients about is Strangles. Strangles is an upper respiratory tract infection caused by the bacteria, Streptococcus equi. For the most part, the disease is reasonably mild, resulting in a snotty nasal discharge, increased temperature, inappetence, dullness and swollen glands. Mild cases, may be completely overlooked, especially if a cough is heard, and passed of as a ‘bit of a virus’.

However, a good proportion of horses infected with Strangles will go onto develop abscesses of the lymph nodes, most commonly those of the head, located under the jaw or behind the cheek, below the ears. These abscesses are the hallmark of the disease and the swelling of the lymph nodes preceding the abscess rupture giving the disease its rather unglamorous and sordid name – ‘Strangles’.

In rare cases, more prolonged and serious complications can occur as a consequence of the infection. Abscesses may form in lymph nodes elsewhere in the body, resulting in prolonged disease and treatment – a condition referred to as ‘bastard strangles’ for literal reasons. Other recognised complications include purpura haemorrhagica, which owners will recognise as limb swelling often with little red spots visible over the gums inside the mouth. This is because the immune system within the body has activated in response to the infection, and may allow the blood vessels to leak.

The biggest trouble with Strangles outbreaks is the rapid spread of the disease. Most of the time spent talking to clients is really focussing on this area answering the question, ‘how do I stop my horse from getting ill?’.

Fortunately, the bacteria causing the disease is easily killed and prevention is straightforward, albeit time consuming. Understanding basic biosecurity principles is important for every horse owner to minimise the chance of contracting and spreading disease, and maximising their horse’s health. As part of the XLVets Equine campaign: Plan, Prevent, Protect, many vets collaborated to create a useful biosecurity booklet describing what you can do to manage disease outbreaks, which is freely downloadable online at http://editions.xlvets.co.uk/plan-prevent-protect/biosecurity/files/assets/basic-html/page1.html

My main topic of conversation currently surrounds blood testing for Strangles infection. This is a very useful test if you take time to understand what the results mean. Confirming strangles as the cause of disease isn’t always straightforward, as the bacteria doesn’t grow readily once outside the horse, so repeated samples may be necessary. Of course, this means that the costs to the owner can be significant, meaning a single blood test appeals greatly.

However, of course there is always a catch. This test purely reflects whether a horse has antibodies to the bacteria or not. A positive result does not tell you whether the horse has active Strangles infection or not. Horses with active infection may well have a positive result, however, in the early stages of infection it is likely to be negative. So what do the results mean?

A negative result shows that the horse does not have significant antibodies against the Strangles bacteria. It takes around two weeks for antibodies to develop, which explains why horses that are in the first two weeks of infection will have a negative blood results, despite being infected. It is therefore important to only use this test after a two week isolation period to be sure the negative result reflects an absence of disease.

Likewise, antibodies will hang around for several months, if not years after infection has resolved. Antibodies can also form without the horse being infected itself, but merely by it being in contact with other horses with the disease. This explains why some horses on a yard which has an active outbreak who have not had the disease can return a positive result – further complicating the interpretation of the results.

In short, while blood testing may seem to be a cheaper and more simple alternative to scoping or having repeated nasopharyngeal swabs done, the most appropriate test depends on your horse’s circumstance and what you are trying to achieve. Prior to moving to a new yard, taking bloods may be the most appropriate test choice; whereas scoping a horse is the fastest and most reliable way of confirming presence of the actual disease itself.

Speaking to your own vet about testing is really important – and you can see why this topic takes so much time out of our day and represents us such a challenge! It’s a good job I can talk the hind leg off a donkey….