October 2, 2019 – Fever, nasal discharge, labored breathing, swollen lymph nodes and difficulty swallowing are hard enough to deal with in dogs and cats. Just imagine the challenges when these clinical signs pop up in a horse, as it does in horses with an upper respiratory infection called strangles.
Strangles, also known as equine distemper, is a highly infectious and contagious disease caused by the bacteria Streptococcus equi equi. The most common clinical signs involve swelling of lymph nodes in the head and neck, especially those under the tongue as well as in back of the throat behind the voice box. The name strangles comes from the fact that swelling of these nodes can physically obstruct the airway, resulting in difficult breathing and, in severe cases, asphyxiation.
The good news is mortality for this disease is relatively low if caught and treated early. For some horses, the infection will resolve itself with little or no intervention. However, in more severe cases, horses can develop serious complications, especially when the bacteria spread to other parts of the body and form abscesses. While prompt care and treatment save lives, prevention via vaccination could stop S. equi equi in its tracks, minimizing and even eliminating the possibility of infection in the first place.
Morris Animal Foundation-funded researcher Noah Cohen, VMD, PhD, and his team at Texas A&M University are working on just that. The team is evaluating a new vaccine strategy for strangles in horses. They hope their novel approach will provide broad protection for horses against S. equi equi while overcoming shortfalls of the currently available vaccine.
“The widely used modified live intranasal vaccine can cause strangles in some horses and trigger other clinical problems,” said Dr. Cohen, Professor and Associate Department Head, Large Animal Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences. “We are working on a strategy that we hope will protect horses from these serious concerns.”
In addition to safety limitations, licensed vaccines against strangles in horses lack strong evidence that they are effective in preventing disease. In addition to safety and efficacy concerns, another pitfall of the currently available vaccine is that it interferes with a commonly used blood test that distinguishes between horses that have been vaccinated and horses with naturally occurring strangles.
“This issue greatly complicates control practices,” said Dr. Cohen. “We hope to be able to develop a vaccine that stimulates both local immunity in the upper airway and systemic immunity to protect against strangles. That will allow us to be able to differentiate vaccination from natural infection. If successful, this new approach will provide much needed information to help control disease outbreaks.”
Strangles is an ancient disease of horses that has been documented for more than a thousand years. It occurs in horses around the world and is considered an important equine bacterial disease, though incidence is difficult to define.
“We don’t have great answers about the incidence or prevalence of strangles,” said Dr. Cohen. “It is not a reportable disease either for the World Organization of Animal Health (formerly known as OIE) or for the United States. Because many cases aren’t reported, it makes it hard to grasp the scope of the problem. What we do know is strangles is a worldwide health challenge in horses and a more effective and safer vaccine is key to prevention and disease control.”
For now, the best defense against strangles is common sense and good hygiene measures. Disease transmission occurs through infected objects including stalls, tack and contaminated clothing; and by direct contact with infectious discharges from affected horses. If one horse in the barn gets strangles, chances are all the horses in the barn have been exposed to S. equi equi and will likely get strangles. The best course of action in a suspected strangles outbreak is to call your veterinarian immediately.