equine influenza

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).

Proactively preventing the spread of flu in animals is important, as animals are the most likely source of future human pandemics. Animals—including horses, pigs, and dogs—can be infected with multiple influenza viruses and have the potential to act as “mixing vessels,” generating new flu strains that could infect people, he said. This hasn’t happened yet, but it’s possible, he added, and these strains would be particularly dangerous, since people wouldn’t have pre-existing immunity.

In their recent study Martinez-Sobrido and lead study author Laura Rodriguez, PhD, said past research has shown that live-attenuated vaccines—made from live flu virus that’s “dampened down” so it doesn’t cause disease—can provide better immune responses and longer periods of protection than vaccines that include inactivated or killed virus.

Created using a genetic engineering technique called reserve genetics, the researchers’ intranasal live-attenuated equine vaccine is designed to replicate and generate an immune response in the nose, where the virus typically first enters a horse’s body, but not in the lungs, where viral replication can cause disease.

The researchers said a single spray of the vaccine protected mice and horses against the currently circulating H3N8 equine influenza virus. The horses tolerated the vaccine well, they said, and vaccination didn’t lead to any negative side effects. Further, vaccinated horses showed no signs of disease when challenged with a natural equine influenza virus. Thomas Chambers, PhD, an assistant professor at the University of Kentucky’s Gluck Equine Research Center, in Lexington, oversaw the vaccination and care of the horses.

The study was small, only involving six horses, but planning for a larger study is underway. Using reverse genetic approaches to create the live-attenuated equine vaccine confers an additional major advantage not available until now: The vaccine can be updated quickly and easily to protect against newly emerging equine influenza strains.

The research was supported by the National Institutes of Health-funded New York Influenza Center of Excellence at the University of Rochester Medical Center and the University of Rochester Technology Development Fund. In addition to Martinez-Sobrido and Rodriguez, a research assistant professor in Martinez-Sobrido’s lab, Rochester scientist Aitor Nogales, PhD, participated in the research. Stephanie Reedy from the University of Kentucky, and Pablo Murcia, DVM, PhD, from the University of Glasgow Centre for Virus Research, in Scotland, also contributed to the study.

The study, “Development of a novel equine influenza virus live-attenuated vaccine,” was published in Virology.