Equine influenza - Horse flu

Equine influenza (Horse flu) is the disease caused by strains of Influenza A that are endemic in horse species. Equine influenza occurs globally, and is caused by two main strains of virus: equine-1 (H7N7) and equine-2 (H3N8). The disease has a nearly 100% infection rate in an unvaccinated horse population that has not been previously exposed to the virus.

While equine influenza is known to affect humans, historically, the impact of an outbreak amongst even the animal population was devastating. Because horses were heavily relied upon for communication (postal service), military (cavalry) and general transport — the social and economic impact of widespread equine disease was devastating. Today the ramifications are most clear in the modern racing industry.

Characteristics

Equine influenza is characterised by a very high rate of transmission amongst horses, and has a relatively short incubation time of 1-5 days.

Horses with horse flu can run a fever, have a dry hacking cough, have a runny nose, and become depressed and reluctant to eat or drink for several days but usually recover in 2 to 3 weeks.

Causes

Equine influenza is caused by several strains of the Influenza A virus endemic to horses. Viruses that cause equine influenza were first isolated in 1956. The viruses can cross the species-barrier to cause an epizootic disease in humans, and recently, in dogs.

The equine-1 virus affect heart muscle, while the equine-2 virus is much more severe and systemic.

The disease is primarily spread between infected horses. Exposure to infected waste materials (urine and manure) in stables leads to rapid spread of the disease.

Prevention

Prevention of equine influenza outbreaks are maintained through vaccines and hygiene procedures. Countries that are equine influenza-free will normally impose strict and rigorous quarrantine measures.

Vaccines

Vaccines are a major defence against the disease. Vaccination schedules generally require a primary course of vaccines, followed by booster shots. Standard schedules may not maintain absolutely foolproof levels of protection and more frequent administration is advised in high-risk situations.

The UK requires that horses participating in show events are vaccinated against equine flu and a vaccination card must be produced; the FEI requires vaccination every 6 months.

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