by: Jeff Cook, DVM
March 27 2007, Article # 9005
The infection caused by the bacteria Streptococcus equi,, commonly known as strangles, has been described in horses for almost 800 years. The name strangles describes the condition in which an affected horse is suffocated as lymph nodes in the throat region become enlarged and obstruct the airway. Many misunderstandings exist regarding strangles, most likely due to horse people passing on tales regarding the infection.
Strangles is characterized by a sudden onset of fever with formation of abscesses under the jaw and within the throat approximately 7-21 days following exposure. These abscesses can open and produce a thick yellow discharge, which might also be seen as a nasal discharge. The symptoms of the disease can vary from severe lymph node enlargement with difficulty breathing to no outward signs with only a slight nasal discharge.
Misunderstandings regarding the transmission of the bacteria causing strangles, Streptococcus equi, exist. It is often said that once a farm has had an outbreak of strangles, the problem will always be on the farm and can show up at anytime. A fact that needs to be understood is that the source of infection from year to year and farm to farm is the horse, not any part of a barn, pasture, farm, or other animals besides horses.
With two to three weeks after outward clinical signs of strangles have ceased, the majority of horses clear the bacteria and no longer pose a threat for infecting others.
However, following an outbreak a number of horses (can be as high as 10%) cannot clear the bacteria and become persistently infected. The bacteria can survive in the guttural pouches, which are located in the pharyngeal region, for years. A carrier horse that undergoes some form of stress such as foaling, weaning, competing at a show, or a simple change in routine, can begin to shed the bacteria and serve as a source of infection for future outbreaks.
Transmission of Strep. equi occurs by either direct or indirect contact. Direct transmission occurs during horse-to-horse contact through everyday social behavior.
The indirect transmission can be more difficult to control and occurs through the sharing of contaminated stalls, water buckets and troughs, feed tubs, and bits. Water sources, either in shared stalls or in field settings with a common water supply, are the most common culprit when it comes to infecting a herd during an outbreak. When a horse is shedding the bacteria and dips their nose into a water source, the water serves as a reservoir for the bacteria to be passed to every horse that comes in contact with the water.
There is a misunderstanding regarding the persistence of Strep. equi in the environment. Besides in a water source, the bacteria will not survive for prolonged periods in the environment. This means horses do not become infected with the bacteria from the soil, grass, or fences unless a horse currently shedding bacteria is present.
Strangles is often diagnosed by clinical signs, but it takes a positive culture with or without a positive PCR test to confirm the presence of Strep. equi. Both tests utilize a sample from a nasal wash or guttural pouch sample or direct swab from an enlarged lymph node. Each test has its limitations, but when used in conjunction can be very effective in detecting the bacteria in a horse showing clinical signs and a carrier horse that might appear healthy.
Once a horse is confirmed to have strangles, they should be isolated from other horses and provided with supportive care to control fevers and ensure an open airway. The best management during an outbreak is to segregate the horses showing clinical signs, and monitoring the temperatures of the healthy horses for two to three weeks after the last horse with clinical signs was removed. Once the affected group of horses is no longer showing signs, they should be tested to confirm they have not become carriers of the bacteria. This is a critical step in preventing future outbreaks.
Steps can be taken to prevent the exposure of your horse to strangles. It is important to remember that a horse does not have to be showing active clinical signs of strangles to be capable of infecting others. Care should be taken to minimize exposure to other horses, particularly at shows and farms with a changing population. When traveling to shows, water buckets should be brought and not shared with other horses. Do not permit direct or indirect contact with other horses while at the show. This includes nose-to-nose contact as well as sharing such things as stalls, water buckets, feed tubs, grooming tools, tack, and trailers.
In a stable or herd situation, a few simple prevention methods can be used to decrease the likelihood of exposure to strangles. Isolation of all horses for two to three weeks before they come in contact with others can decrease the potential exposure. Testing incoming horses for Strep. equi can be an effective tool in limiting the introduction of strangles into a herd or stable. Strangles is a preventable disease and with the proper steps, the risk of exposure can be minimized.
Ask your veterinarian how they can help you protect your horse and farm from this preventable disease.
Article courtesy of The Kentucky Equine Education Project (KEEP), www.horseswork.com.