Saturday, March 5, 2011
We have encountered some isolated cases of Strangles at a couple of different barns already this year. Strangles is a highly contagious bacterial respiratory infection that affects horses. Affected horses can get quite sick, usually with fevers above 103F, depression, nasal discharge, cough, and greatly enlarged lymph nodes under the jaw or at the base of the neck which usually go on to rupture and drain. The disease is so named because the lymph node swelling can become so severe that it impinges on the air passages. Though affected horses become quite ill, the disease is rarely fatal.
The most significant issue surrounding cases of Strangles is the highly contagious nature of this bug. The disease is transmitted from horse to horse primarily through nose to nose contact or through shared water sources. It is also possible for the bacteria to be spread by handlers, shared tack or grooming equipment, barn cleaning supplies, etc. For these reasons it is best to isolate affected horses. This can become a real challenge as most barns do not have an isolation facility or housing separate from the rest of the horses. In such circumstances, we recommend moving affected horses to one end of the barn, close to an outside door (so the horse does not have to walk through the rest of the barn to go outside). There should not be any opportunity for direct nose to nose contact with other horses. It is imperative that water buckets not be shared. Affected horses should be fed and handled last. Stock tanks should be emptied, thoroughly sanitized and allowed to dry. Pastures that have housed infected horses should be left unused for 30 days before they are put back in use.
One of the frustrating aspects of Strangles infections in populations is that the first horse to become infected is rarely the source of the infection. The disease is usually brought in by new horses to the barn that are, unbeknownst to anyone, shedding the causative organism. Often the horses shedding the bacteria are no longer ill and otherwise seem healthy. The only way to identify asymptomatic shedders is to submit samples from each horse for either culture or PCR (polymerase chain reaction). PCR testing is a very good way to identify horses shedding the bug. The PCR test identifies the DNA from the causative bacteria, however, the test does not tell us if the bacteria are alive or dead, just that their DNA is present. For that reason, culturing is often done concurrently with PCR testing.
It is very difficult to know for certain that there is no longer any risk for infection at a barn that has had a recent case. The generally accepted recommendation is to not bring any new horses into or out of the barn for one month beyond the last clinical case. The first clinical signs are usually seen 2-6 days after exposure, but there are reports of it taking up to 2 weeks before symptoms take hold. An additional consideration is that recovered horses may continue to shed bacteria for many weeks, even though they are no longer ill. Because of all of these variables, in the absence of testing every horse, the general recommendation of a one month quarantine from the last clinical case is often made.
Strangles is certainly one of those diseases that is much better to prevent than to have to deal with. There are a couple of different vaccines available for Strangles. They each have their advantages and disadvantages. Talk to your veterinarian about specific vaccine recommendations for your individual situation. Strangles is not one of the core vaccines that we always recommend every horse have every year. However if your horse is considered 'at risk', it certainly makes sense to vaccinate. We generally recommend vaccinating if your horse is stabled with horses of unknown background or if you are taking your horse into barns or herds where there are other horses that also get out and have exposure to other horses in other places. Generally, if you do not travel with your horse and they do not have significant exposure to other horses of unknown background, then vaccination may not be necessary. Good hygiene and common sense go a long way in preventing and limiting the spread of this disease. New horses coming into a barn should be isolated from the rest of the herd for 14 days. Do not share water buckets or let them drink from stock tanks at shows or barns you may visit. When travelling with your horse, do your best to limit nose to nose contact with other horses. Unfortunately, even when good precautions are taken occasional flare ups of this disease still occur.
The best source of information about specific recommendations for the prevention and management of Strangles cases is still your regular veterinarian. The impact of and the stigmas attached to this disease make it very worthwhile to implement good prevention strategies.