Strangles is a highly contagious, infectious disease of the upper respiratory tract and can be serious or occasionally even fatal as a result of late diagnosis. Know what to look for and you will almost certainly avoid the unnecessary suffering of your horse and others. Rarely, complications can occur such as bastard (metastatic) strangles, where abscesses can form elsewhere in the body, and purpura haemorrhagica, where the body’s immune system starts attacking the body tissues.
The disease is spread either directly from horse to horse or indirectly via fomites (inanimate objects). Direct infection occurs by bacteria being shed in the discharge from the nose or abscess of an infected horse coming into contact with a non-infected horse. Also importantly disease can come from the nose of horses showing no signs of disease (shedders or carriers). Indirect infection occurs when the bacteria being shed from the horse’s nose or discharge from an abscess is carried to other horses by any object, such as people’s hands/clothing, tack, grooming and yard equipment (fomites). The incubation period is up to 14 days, so there can be up to 21 days between cases showing signs of infection as the abscesses can take up to a week to appear. All horses are susceptible. Recovering hoses can shed the bacteria for 6 weeks. About 10% of horses recovering from the disease will carry the bacteria within their head (in the guttural pouches) and will be healthy horses, but intermittently be a source of bacteria for months to years that can infect other horses. Identifying these carrier horses is key to stopping the outbreak re-occurring on your yard and preventing spread from yard to yard.
How do I know if my horse has strangles?
Fever (above 38.5℃) accompanied with depression and loss of appetite.
Profuse yellow nasal discharge from both nostrils (thick mucus).
Swellings on the side of the head and throat which may burst and discharge pus. These abscesses are usually hot and painful and occur some days after the initial fever.
Sore throat – difficulty eating, extending the head.
Atypical strangles (becoming more common, especially in healthy adult horses)
Mild short term fever – may loose appetite for a brief period of time.
Mild clear nasal discharge.
No abscess formation.
These horses are a risk to other horses and should be treated as infectious.
NB: These clinical signs can be seen with a wide variety of diseases and not just strangles.
Isolating affected horses and seeking immediate veterinary attention is essential to stop the spread of the disease.
Diagnosis of an individual horse is based on identifying the bacteria cultured (or PCR) in a lab from throat swabs or aspirates/swabs from abscesses. However, not all strangles cases will have a positive result.
A new blood test (serology) is available that detects antibodies to the bacteria, the antibodies take up to two weeks to form and stay elevated for up to six months after infection. A guttural pouch wash using an endoscope is the best ay to ascertain if a horse has the disease.
Strict hygiene and disinfection protocols are essential. Creating an isolation area which has a foot dip and specific overalls is important.
If the diagnosis is positive either based on clinical signs, culture, PCR or blood test then your vet will discuss treatment options with you.
Most cases just need intensive nursing care including rest and a dry environment.
Feeding soft palatable feeds is important.
Abscesses can be hot-packed to encourage them to burst.
Use of antibiotics in strangles cases remains controversial and should be judged on an individual patient basis by the attending vet.
Recovering horses can shed bacteria.
Culture and PCR of three throat swabs (nasopharyngeal) 5-7 days apart – any horses returning positive results need guttural pouch lavage via endoscopy.
Culture and PCR of one guttural pouch lavage via endoscopy.
Serology blood test – any horses with positive results need guttural pouch lavage via endoscopy.
Preventing strangles entering a yard involves isolating all horses for three weeks. Consider performing serology blood test on all new horses moving on to a yard. Unfortunately there is no licensed vaccine available in Europe for Strangles at the moment. A vaccine was launched in 2005, Equilis StrepE, but was withdrawn due to manufacturing problems; however it may return to the market in the future.
Recently the Parkside Equine dealt with an outbreak of strangles on a yard in this area after a horse was introduced onto the yard. This horse was a carrier and spread the disease to lots of other horses, some showed clinical signs and others did not. One horse developed purpura haemorrhagic and was referred to the Dick vet for intensive nursing and treatment and fortunately survived. A testing process was put in place to identify affected horses, until all horses were clear except for the carrier horse. We investigated this horse with our endoscope and found it to have chondroids (lumps of pus) in its guttural pouch which were removed surgically at the Dick Vet.
The yard is now happily free of the disease after all their hard work and perseverance.