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You are here: Home / Articles / Equestrian Life

Reducing the spread of strangles

Kathy Carter

Strangles is highly contagious but there are measures that can be followed to reduce its spread

According to Tim Mair MRCVS, specialist in equine internal medicine, most outbreaks of strangles are caused by a new horse coming on to a yard.

"This is because it can be difficult when purchasing a horse, or introducing a horse to a yard if you are not the owner, to find out if it has been exposed to strangles," he explains. "So-called 'carrier horses' may appear outwardly healthy but can in fact be harbouring the disease."

What is a carrier?

Carriers are horses which have recovered from strangles, but remain infected by the Streptococcus equi bacterium. Most of these horses will be protected from catching strangles themselves for up to five years.

According to Animal Health Trust (AHT) head of bacteriology Andrew Waller, most carriers have developed clinical strangles at some stage previously, although they may have exhibited only minor clinical signs.

"As horses recover from the disease, around one in 10 may remain infected by Strep. equi and become carriers," he explains. "These horses may appear completely healthy, but intermittently shed the bacteria, which can then infect other horses. They make a significant contribution to the number of new strangles outbreaks each year."

Marketing executive Lyndsay Langdon, from Berwickshire in Scotland, bought her horse Springer in 2005 after a five-stage pre-purchase vetting. Springer was turned out with one other horse at the yard where Lyndsay had been a livery for several years. However, around 10 days after the vetting, Springer became slightly ill, with a nasal discharge and lack of appetite.

"We thought it was a virus," recalls Lyndsay. "However, within days, his fieldmate and many of the other horses became ill with varying signs. It took three positive swabs from one of the other horses before the vets actually diagnosed it. It was concluded that Springer arrived with a mild form of the disease. I still feel terribly guilty. When a contagious disease reaches an enclosed yard, it spreads like wildfire. It took three months for the yard to get the all-clear, and almost half the horses contracted strangles."

Is your horse a carrier?

AT present, there are two main ways of discovering a horse's status. One is guttural pouch endoscopy, whereby the guttural chambers at the back of the jaw are washed out and cultures taken and tested. The second more simple method is to have laboratory tests performed on nasopharyngeal swabs (long swabs that reach the back of the throat). Three tests are usually taken at intervals of 5 to 7 days.

Julianne Aston of the Veteran Horse Society says screening of new equine arrivals to her rehabilitation centre is stringent.

"Our vet takes nose swabs from each new horse. If strangles were brought to the centre, it would be catastrophic for us," she explains.

Taking swabs is a cheaper, less invasive, but not completely reliable method of diagnosis than endoscopy. However, neither test is commonplace when new horses are purchased, according to Tim Mair, as they do not identify 100% of cases.

Andrew Waller believes that, in theory, performing such tests at the vetting stage of a purchase would be a good thing, but acknowledges that endoscopy is expensive and invasive and that swabs are less failsafe.

"The AHT is working on a diagnostic blood test, which we hope will be much more useful; it should identify any horse that has been exposed to strangles in the recent past and we hope it may also identify carriers," he says.

So what should you do?

According to H&H's vet Karen Coumbe MRCVS, the best way to minimise the spread of strangles is to spot the signs early, isolate suspected cases immediately, and contact your vet. Usually, the diagnosis can be made on clinical signs but confirmation currently requires tests. Ideally, confine new horses for at least two weeks. Any horse showing signs needs to be in quarantine for a longer period.

"The disease is commonly spread through close contact, so isolation procedures are key. Direct contamination of the environment, for example, bacteria shed from a draining abscess and/or the horse's nose, is also a risk, so hygiene is important too," she explains.

This vet feature was first published in Horse & Hound (10 May, '07)