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Dukes Equine Vets Ltd
How we approached a Strangles case
We were initially called to visit a horse that was not eating in a small livery yard. Following a clinical examination the horse was blood tested for Strangles (Strep. equi respiratory infection). The result came back antibody positive and the yard was advised not to allow horses on or off the premises. The horse was put in isolation and biosecurity measures introduced. A horse that is antibody positive does not necessarily have Strangles but this horse was subsequently showing classic clinical signs.
All the in contact horses were blood tested. None of these horses have shown clinical signs but some were antibody positive suggesting recent exposure to S.equi. In order to identify if the infection was present in other groups all other horses on the premises with possible contact with the infected group were then blood sampled.
Some of these horses had attended a pony club rally just before infection was diagnosed. As none of these horses were showing or have since shown signs of S.equi infection then we believed that the risk of spread of infection from indirect contact was small but not nil. Horses are always at risk of picking up an infection when mixing with horses from other premises. We did not suggest cancelling other events in the area.
Owners of any other horses at the rally that may have had contact with any of these horses were advised to monitor their horses closely for any signs of disease and if they were suspicious contact their vet. Classical signs are an elevated rectal temperature >38.5oC or >101.5oF, swollen glands which may burst and discharge under the chin or at the back of the jaw or under the ears, coughing and a nasal discharge. The horses can become quite sick and may stop eating due to painful swelling in the throat. The incubation period for strangles is usually 7 – 10 days but occasionally 14 days or longer. In this case none of the other owners reported that any of their horses that attended the rally had become infected.
The origin of the outbreak was unknown, no horses had been introduced onto the premises in the last few months and the horse showing signs of infection had not been off the premises in the last few months. Further tests were undertaken to try and identify if the disease had spread to other horses on the premises and a protocol was put in place to identify the extent of the problem and the yard was put into isolation.
Carrier horses occur that can be infectious without showing clinical signs. This case may have been as a result of contact with a carrier horse. There is no 100% accurate method of detecting carrier horses but we would advise that a Strangles test is part of any biosecurity procedure for new horses coming on to a yard. If you wish to set up or modify the biosecurity protocol for your yard contact your vet for advice.
In this case the source of the outbreak was not identified, all horses showing signs of infection were treated and the horses were subsequently divided into two groups. All antibody positive horses were endoscoped and had gutteral pouch wash samples taken and sent to the Animal Health Trust for diagnosis by PCR. One of these came back positive and the horse was quarantined off from the rest and subsequently retested negative. The previously negative in contact horses were re-sampled and all came back negative showing the disease had not spread. It’s important to know that no test for Strangles is 100% sensitive and it is possible for an infected horse to test negative. However if there is no evidence of spread this strongly supports the yard being clear of infection. After a further two weeks symptom free the yard was declared Strangles free and no relapses have occurred.
The protocol we suggest is different for each case depending on the factors involved but this system has worked well for us in all the outbreaks we have used it in.
Further information on Strangles is available at http://www.aht.org.uk/strangles.org/index.html and there is an excellent downloadable pdf summary http://www.aht.org.uk/strangles.org/pdf/steps.pdf