Clinical signs of infection in horses include fever, appetite loss, lethargy, coughing, and nasal discharge (watery at first but typically becoming mucopurulent). | Photo: The Horse Staff

Scientists have developed a new live-attenuated vaccine to protect horses against equine influenza.

Luis Martinez-Sobrido, PhD, associate professor of microbiology and immunology at the University of Rochester Medical Center, in New York, said a new vaccine is needed not only to keep horses healthy, but also to protect people in the future.

Influenza virus is the most common cause of viral respiratory tract disease in horses and has a substantial economic impact on the horse industry annually. Outbreaks occur most frequently when susceptible animals are housed in close contact with one another, as is typical at racetracks, sales barns, and horse shows. Clinical signs of infection in horses include fever, appetite loss, lethargy, nasal discharge (watery at first but typically becoming mucopurulent, meaning it contains pus and mucus), and coughing. In uncomplicated cases clinical signs resolve in approximately seven to 14 days, although coughing might persist longer. Complications can be severe and might include secondary bacterial pneumonia, myositis (muscle inflammation), myocarditis (heart muscle inflammation), and limb edema (fluid swelling)