When strangles strikes, Part II

In the face of an outbreak, most people feel that vaccinating the unaffected horses (those that are not showing any clinical signs or have developed a fever) will help reduce the severity of the disease if they do contact it. It may not prevent them from acquiring it, but it will provide some immunity...In the face of an outbreak, most people feel that vaccinating the unaffected horses (those that are not showing any clinical signs or have developed a fever) will help reduce the severity of the disease if they do contact it. It may not prevent them from acquiring it, but it will provide some immunity...

Story originally posted by: Michael Lowder, DVM, MS

Ok, now that we have an outbreak at the barn, the big questions are: (1) do I vaccinate and if so, whom, (2) what is going to be my veterinarian’s role in the management of the sick horses and (3) what is the long-term impact on my herd.

In the face of an outbreak, most people feel that vaccinating the unaffected horses (those that are not showing any clinical signs or have developed a fever) will help reduce the severity of the disease if they do contact it. It may not prevent them from acquiring it, but it will provide some immunity. There are two basic types of vaccines on the market now: an intramuscular [IM] and intra-nasal
[IN] vaccine. Which one is best for your situation will depend upon your herd, and your veterinarian can best advise you.

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If any of the affected horses develop difficulty breathing, difficulty swallowing, prolonged high fever, severe lethargy or go off feed for a few days, your veterinarian should be called. If the difficulty in breathing is severe enough, she may perform a tracheostomy (surgical construction of a respiratory opening in the
trachea) to help the horse breathe. In severe cases of swallowing problems and fever, your veterinarian will administer medication to control swelling and reduce the fever. Procaine penicillin G is often the antibiotic of choice and should be given for five to seven days after the resolution of clinical signs.

What is the long-term impact for the herd? A few horses may develop purpura hemorrhagica, which is an immune mediated vasculitis that usually occurs two to four weeks after the clinical disease has ended. It has also been known to follow vaccination or subclinical infections. The affected horses will continue to shed the infection for about one month after their clinical signs have resolved. All affected horses should be isolated for a minimum of one month and longer in some cases. The best way to know if your horse is no longer shedding the bacteria is to have three nasopharyngeal swabs taken at four to seven day intervals. All three samples must be negative. Some horses have been known to shed the bacteria for a year after initial infection.

Survival of the bacteria depends upon the temperature and humidity. The bacteria will die if exposed to sunlight, extreme heat and desiccation. In the best environment, the bacteria can survive as long as two months. All facilities used by infected horses (paddocks, stalls, tack, buckets, etc.) should be regarded as infected for this period of time. The contaminated environmental areas can be sprayed with a 1:200 solution of phenol with water. Be sure not to use this on
water and feed buckets. They will need to be washed with a mild detergent and rinsed thoroughly. Sun dry the buckets after washing.

Remember that it is cheaper to isolate new horses than it is to treat. Boarding stables should require documented vaccination prior to arrival (four to six weeks prior is a good choice) to help protect the resident population. Show horses and horses from open herds (those in which different horses come and go) should consider vaccination against strangles. Remember to consult with your local veterinarian prior to vaccinating, as they will know what is best for your herd and will have the most current information.