‘Tis the season

With the children on school holidays and the show season hotting up, sadly the risk of spread of some infectious diseases in our equine companions inevitably increases. One of these is the respiratory infection with the bacterium Streptococcus equi equi, commonly known as “Strangles”. Generally strangles is seen in young or elderly horses or donkeys, with many middle aged equids having some immunity to the disease from previous exposure or vaccination. Infection occurs when susceptible horses have direct contact with infected horses, or indirect contact with contaminated items such as feed/ water containers, stables/ bedding, tack, rugs, grooming kit, transport vehicles and handlers’ hands or clothing.

Strangles affects the upper respiratory system, and rarely, in more complicated infections can affect the lungs or spread to lymph nodes in other parts if the body. 3-8 days after infection with the bacteria, susceptible horses develop a fever (39°C-40.5°C) and become depressed, off food and lethargic. Affected horses sometimes cough, and often have a cream discharge from their nose. In worse cases the lymph nodes in the throat area become swollen and painful, and can develop into large pus-filled abscesses which make swallowing difficult and cause noisy breathing.

These clinical signs last for days to months. In most cases, the abscesses around the throat area eventually burst (often takes 2-3 weeks), the pus drains out and then most horses recover relatively quickly afterwards. After the abscesses have drained and healed, horses remain infectious to others for at least four weeks. Some horses can become “carriers” of the disease, and so despite having no symptoms, carry the bacteria in parts of their respiratory tract and these can be shed intermittently for months to years after infection. These “silent” strangles cases are often the source of infection in an outbreak as the horses do not appear sick and so are allowed to mix with others.

Diagnosis is often based on clinical signs- a high temperature, nasal discharge and a swollen throat should make any owner suspicious. A formal diagnosis can be made by your vet. Swabs can be taken from the respiratory tract or abscesses and be sent off to a lab for culture, and if Streptococcus equi equi is grown then this is a positive diagnosis. Results usually take 2-4 days.

The disease is painful and distressing for both horse and owner. Speak to your vet for advice if you are suspicious your horse may have it. Anti-inflammatories for a few days can alleviate some of the pain, and will reduce the fever, making most horses feel better and improving their appetite. Whether to treat patients with antibiotics is a much-debated matter. Antibiotics don’t penetrate abscesses well and antibiotic treatment can in fact prolong the disease process, with abscesses taking longer to burst out and drain. I assess each case individually, taking into account the horse’s age, immune status, whether their ability to eat/drink or breathe is affected, and only give antibiotics in a small number of cases. In the mild to moderate cases I see, I believe that the immunity a horse develops from natural infection and resolution is important, and the best way to prevent future infection.

A vaccination for strangles is available, and can be given as a “2-in-1” with tetanus. Horses over three months of age require a primary course of three vaccinations. It is recommended that the interval between doses should be 2-4 weeks, followed by an annual booster, or 6-monthly booster if the risk of exposure to strangles is high.

Strangles is no longer a notifiable disease in NSW, so owners and vets are not obliged to report cases. However, as a responsible owner, precautions including strict hygiene procedures should be enforced to help prevent the spread of the disease. Wear gloves and separate clothes and boots when handling infected horses. Keep all equipment, stables, feeding buckets etc. separate and disinfect regularly.

Take home message:

If you suspect your horse has strangles then quickly isolate him/her from other horses, unless they have been in close contact or grazing with others recently as the infection is likely to already have spread to these horses.

Contact you vet for advice on management/ treatment options.

Don’t travel your horse unless absolutely necessary.

Don’t take your horse to competitions or to a new yard until at least 4-6 weeks after all symptoms have resolved.

Strangles has become a taboo subject amongst horse owners, but it should not be. It is not a reflection on your horse owning skills, or an indication of poor health and hygiene on a yard, it is merely a disease that is endemic in horses in Australia, and most will come into contact with at some point in their lives. Honesty amongst vets and owners, a sensible approach to testing and treating cases alongside quarantining new horses and a proper vaccination protocol is paramount in protecting our beloved horses from this horrible disease.

Jessica Austin BSc (Hons) BVetMed MRCVS


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