Is a Respiratory Virus Behind Equine IAD?

While direct cause and effect has not yet been proven, researchers identified a strong association between horses developing asthma after contracting a rhinitis virus.

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Inflammatory airway disease (IAD) in horses is similar to asthma in humans. In both cases, inflammation in the lungs leads to poor respiratory function and can limit an affected individual’s ability to perform aerobic activities. Researchers know that, in humans, rhinoviruses are responsible for the common cold and can also trigger asthma development. Veterinarians and researchers have long suspected a connection between an equine respiratory pathogen—rhinitis virus—and IAD development, but this theory remains just that—a theory.

So, researchers recently set out to get a better idea of whether rhinitis virus could, in fact, play a role in IAD development.

“Rhinitis virus and the role it plays in the development of equine disease has taken a backseat to more dramatic viral infections like influenza and rhinopneumonitis, (the latter of which is) caused by equine herpesvirus (EHV)-4 and -1,” explained Melissa Mazan, DVM, Dipl. ACVIM, Large Animal Section Head at Tufts University’s Cummings School Of Veterinary Medicine, in North Grafton, Massachusetts.

These more severe respiratory viruses can keep a horse laid up for weeks with respiratory signs, fever, and muscle aches, Mazan said. Equine rhinitis virus clinical signs, on the other hand, are less severe and more similar to the common cold in humans.

Through their study, Mazan and colleagues determined that horses with IAD were significantly more likely to have previous exposure to equine rhinitis virus (68%) than control horses without IAD (32%). Further, IAD horses were more likely to have exposure to another equine respiratory pathogen (EHV-2) than controls.

Mazan said this study gives researchers further reason to continue exploring viral respiratory disease as a trigger for development or exacerbation of IAD, but other factors that can adversely affect a horse’s respiratory health must be taken into account, as well. Management plays a significant role in reducing a horse’s chances of developing asthma, she said.

For instance, if your horse with respiratory issues eats hay, choose a high-quality hay and wet it prior to feeding to reduce the amount of dust it contains, she said. She also recommended:

  • Vaccinating horses against respiratory disease, when possible. The caveat, of course, is that there are not currently vaccines for all the respiratory viruses that affect horses. But be proactive and take advantage of the ones that are available;
  • Limiting interaction with other horses when you and your horse travel or when a new horse arrives at your property;
  • Avoiding sharing food and water buckets;
  • Disinfecting bits before using them on different horses. “Kids who wear retainers wouldn’t share it with a friend; we don’t always take the same precautions with our horses,” she added; and
  • Keeping horses out of the barn while feeding and cleaning, the two times when dust in the air is likely to be very high.

While direct cause and effect has not yet been proven, there is a strong association between horses developing asthma after contracting a rhinitis virus. “There is merit for further investigation into the relationship between respiratory virus exposure and the development of IAD,” Mazan concluded.

The study, “Association between inflammatory airway disease of horses and exposure to respiratory viruses: a case study,” was published in the Multidisciplinary Respiratory Medicine Journal

About the Author

Katie Navarra

Katie Navarra has worked as a freelance writer since 2001. A lifelong horse lover, she owns and enjoys competing a dun Quarter Horse mare.

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