Japan reports first outbreak of equine influenza since 2008

Preventive measures were currently underway, including isolating infected horses, suspending the movement of other horses, administering vaccines, and disinfecting facilities to contain the spread.

Equine influenza is a highly contagious viral respiratory disease that affects horses, donkeys, and other equine species.

The latest report of the disease marked the first outbreak of equine influenza in Japan since 2008, Xinhua news agency reported. A previous outbreak in 2007 led to the cancellation of central horse racing events.

Equine influenza is highly infectious and spreads rapidly among naive horses. Outbreaks in susceptible horse populations are associated with considerable economic impacts. China, Japan, and Australia experienced devastating epidemics of equine influenza affecting tens of thousands of horses in 2007.

Horses 1–5 years old are the most susceptible to infection, particularly when housed in large groups. Horses that are immunosuppressed for various reasons (traveling, training) may have an increased risk for infection and more severe disease.

Transmission is most commonly direct via inhalation of infective respiratory secretions from coughing horses. Indirect transmission via fomites (clothing, hands, shared water) should also be considered an important mechanism of disease transmission.

Shedding is longest in naive horses and lasts 7–10 days after the time of infection. Epidemics arise when one or more acutely infected horses are introduced into a susceptible group.

Vaccinated horses can act as subclinical shedders. The epidemiologic outcome depends on the antigenic characteristics of the circulating virus and the immune status of a given population of horses at time of exposure.

Frequent natural exposure or regular vaccination may contribute to the extent of antigenic drift seen with specific strains of A/equine-2 virus in some parts of the world.