A healthy horse that has nose-to-nose contact with a sick horse might not show clinical signs, but still could be shedding virus because it has been infected. | Photo: iStock

Due to its potentially devastating economic impact, researchers have been hard at work studying this contagious respiratory disease

Equine influenza epidemics date as far back as 433 A.D. In more recent times, an 1872 outbreak in Canada and the northeastern United States brought all equine-based commerce, transportation, and services to a standstill—an estimated 80-99% of horses in the region were affected, with 1-2% dying. It only took 90 days for this epidemic to spread from Toronto, Canada, throughout the United States and as far south as Cuba. In an era when everything depended on transport via horse power, this had a staggering effect on daily life.

In 1987 in India, an outbreak involved the infection of 27,000 horses. In Australia in 2007, imported horses from Japan became the index cases of influenza that, due to biosecurity lapses, circulated from the quarantine station to infect 70,000 naive (never exposed or vaccinated) Australian horses, wreaking losses of a billion dollars in productivity and function.

You can see why researchers worldwide are so motivated to study this highly contagious disease and develop effective vaccines to protect the horse population