CSU Researchers Developing New Test for Strangles

Equine researchers at Colorado State University's James L. Voss Veterinary Teaching Hospital are developing a faster and simpler test to determine a horse's level of exposure to strangles. Currently, tests exist only for horses with active signs of disease.

The test method is an enzyme-linked immunosorbant assay (ELISA) test, which would provide veterinarians with a tool to quickly and easily determine a horse's risk level by assessing the animal's blood antibody titer. If an animal has been exposed, either through illness or vaccination, the body's natural response is to form circulating antibodies to fight the bacteria. Therefore, a low titer translates to a very high-risk level for contracting the disease if exposed.

"For example, a horse about to be shipped to a farm where a case of strangles has already occurred would have a very good chance of contracting the disease," said Dr. Ann Davidson, one of the equine veterinarians working on the development of the test.

"If an owner is aware that his horse is in the high-risk category, he now has the option of electing not to ship the horse at all or to begin a series of vaccinations to protect it.

Strangles is a highly infectious disease in horses that affects the upper respiratory tract and the lymph nodes surrounding the throat, causing swelling and abscessation.

In severe cases, the swelling makes it difficult for the horse to breathe, thus the name strangles. Streptococcus equi, the bacterial agent that causes the infection, is found worldwide and has been recognized for centuries. It can affect horses of all ages, but younger horses are more susceptible.

"One of the challenges in diagnosing strangles lies with horses that are not exhibiting signs of active illness, but are carriers shedding the bacteria." It is often through contact with these shedders that other horses can become infected.

The current gold standard for testing symptomatic horses is a laboratory culture of the nasal discharge or abscess material. Another method is a polymerase chain reaction test (PCR).

"The advantage to the ELISA test on the horse's serum is that we can now determine those horses who may not have been exposed and are at risk. Once perfected, we hope the test results will be rapid and readily available, making it a very useful tool for equine veterinarians," said Dr. Josie Traub-Dargatz, another of the test's researchers.

The funding for this research came through a special grant from the USDA, the Cooperative State Research Education and Extension Services for the Colorado State University Program for Economically Important Infectious Animal Diseases, and the College Equine Research Advisory Council On The Use of Racing Funds for Colorado State University's College of Veterinary Medicine and Biomedical Sciences.

Peter Owen and Dr. Mary Meehan in the Department of Microbiology at the Moyne Institute of Preventive Medicine, Trinity College, Dublin, Ireland provided additional assistance.