Pet Columns, Office of Public Engagement, College of Veterinary Medicine at the University of Illinois at Urbana-Champaign

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Stomping Out Strangles: A Researcher's New Vaccine May Help


Pet Column for the week of March 5, 2009


Office of Public Engagement
2001 S. Lincoln Ave.
Urbana, Illinois 61802
Phone: 217/333-2907
Ashley Mitek
Information Specialist

Swollen lymph nodes beneath your jaw are a common occurrence in human medicine. While they are not usually a major concern to physicians, mention to an equine veterinarian that your horse has large swellings on the side of its neck and their reaction is quite the opposite.

"Strangles is a highly contagious disease in horses affecting the submandibular and retropharyngeal lymph nodes," says Dr. Luke Borst, a pathology resident at the University of Illinois College of Veterinary Medicine. He has spent quite some time studying this ancient equine ailment and is working on a new vaccine to prevent it from wreaking havoc in boarding barns across the country.

The bacteria Streptococcus equi causes the infection and it can easily be transmitted from horse to horse by nasal secretions. Although the first sign of the disease is fever, what owners usually notice are enlarged lymph nodes that eventually burst.

There are two issues that require attention to control strangles. "First, we need to be able to identify individual carriers," explains Dr. Borst, and "secondly, we need an efficacious vaccine that has the potential to eradicate the disease." Several vaccines are already on the market, but their safety and effectiveness is controversial.

One of the primary concerns that Dr. Borst's research has highlighted is that vaccines appear to be responsible for unacceptable complications in horses younger than 6 months of age. To complicate this, young horses are more prone to develop a severe form of strangles, and they are the age group that needs added protection.

In addition, with the current strangles vaccines, vaccinated horses cannot be differentiated from an infected animal via a blood test during an outbreak. Dr. Borst is hoping to create a vaccine that will be "flagged" so it is distinguishable from an infected animal. He has also been able to delete the virulence genes in his vaccine to make it less likely that an animal will get sick from vaccination.

Dr. James Brendemuehl is an assistant professor at the University of Illinois Veterinary Teaching Hospital in Urbana. He has treated several cases of strangles over the years, including an outbreak in 150 mares with foals, and more recently in a herd of yearlings. He explains that, "strangles is really a slang term from the fact that in some cases lymph nodes become so swollen the animal can't breath."

Despite how unsightly an abscessed lymph node looks, it is generally recommended that antibiotics not be administered because they may complicate disease progression. "We use anti-inflammatory drugs to help keep temperatures down, but usually we let the disease run its course," notes Dr. Brendemuehl.

While strangles is not usually fatal in older horses and most animals become immune to the bacteria after one exposure, the major problem is identifying carriers. Once a horse has contracted strangles, they continue to shed the disease for several weeks, and sometimes longer. Until a previously infected horse has had three repeat tests come back negative, the animal may still be infective to others.

Dr. Brendemuehl also mentions that stress, such as from shipping, tends to make outbreaks more likely, and they frequently see more cases in the winter because horses are more often housed in close quarters.

Because vaccination depends on several factors, talk to your local veterinarian if you have questions.