As a horse owner or potential horse owner, it is important for you to understand the equine disease called strangles. Caused by the organism Streptococcus equi, it is a very contagious disease that can easily take over a farm if proper precautions are not taken. With proper management techniques, however, an outbreak of strangles can be reasonably controlled, minimizing the effects of the disease on any other horses.
Strep. equi is spread directly by contact with infected horses or carriers. It can also be spread indirectly through fomites that have been contaminated by respiratory tract secretions or saliva. Equipment such as water buckets, halters, fences, and walls may serve to transmit the bacterium to an uninfected horse. Usually, the organism is ingested or inhaled. Clinical signs include high fever, depression, anorexia, profuse mucopurulent nasal discharge, and swelling and abscessation of the submandibular and retropharyngeal lymph nodes and lymph nodes of the head and face.
A horse suspected of having strangles usually has a high fever and swollen lymph nodes around the head and face. The first step in proper management is to isolate this suspected case of strangles immediately. By isolating the horse you are protecting any other horses on the property. The only way to get a definitive diagnosis of strangles is via culture, so you must have the veterinarian examine the horse and get a sample to send to the lab.
In normal circumstances, a horse with strangles needs time to let the disease run its course. You should make the horse as comfortable as possible by providing proper housing and good quality feed. If the lymph nodes are swollen they may develop an abscess which usually break and drain. Try to encourage external rupture and drainage by applying hot packs to the swollen areas. In some cases, using phenylbutazone (bute) to reduce fever, pain, and swelling can also be helpful. 15% of horses with strangles will develop complications including internal abscessation of the lymph nodes of the chest, an allergic reaction to the cell wall of the bacteria resulting in purpura hemorrhagica, respiratory distress, and death.
Keep the horse isolated for at least 6 weeks, even if all signs and symptoms are gone as horses can shed the organism for this long. In some cases, horses will shed the organism for up to 4 months. Also, the person providing care for this horse must make every effort to minimize contact with other horses. Just as a water bucket or halter can serve as a transmitter of the disease, so can a person who has been contaminated by any respiratory secretions or saliva.
Many people wonder how strangles can show up some place where there have not been any horses sick with the disease. Usually, outbreaks are initiated by introduction of asymptomatic horses still shedding the organism after infection, horses that are still incubating the disease, or carrier horses. These horses are not showing any clinical signs of the disease, thus, they could be mingling with other horses and transmitting the disease even though they are recovered from the disease or have not yet developed clinical signs. The incubation period for strangles is 3-14 days so keeping new horses isolated for this amount of time to ensure they are healthy reduces the chance of spreading the disease.
My experience with strangles leads me to believe that some horses are carriers of Strep. equi. Though rare, these horses harbor Strep. equi within their lymph nodes or mucous membranes all the time. When they are stressed by hauling, crowding, hot weather, etc., Strep. equi becomes present in their nasal secretions. As the carrier horses drink at the stock tank and greet their susceptible neighbor nose to nose the disease is transmitted. In the susceptible horse the disease will become clinically evident in 3-14 days.
A vaccination against strangles is available and has been proven to be relatively effective. It may not fully protect against the disease, but it lessens the incidence and severity of the disease. A new form of the vaccine, called Pinnacle I.N. (intranasal), has eliminated many of the negative side affects associated with the older intramuscular injection. For horses that have not been vaccinated against the disease previously, we recommend 2 vaccinations given 3 weeks apart and then a twice yearly booster. We especially recommend this vaccination for horses that travel away from their farm frequently and will be in contact with other strange horses (show horses, trail horses, etc.). As always, contact your veterinarian if you have any questions or concerns regarding strangles.