Equine influenza (Horse flu) is the disease caused by strains of Influenza A that are enzootic 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 with no prior exposure to the virus. While equine influenza is historically not known to affect humans, the impact of an outbreak would have been devastating. Since people heavily relied upon horses for communication (postal service), military (cavalry) and general transport, the social and economic impact of widespread equine disease would have been devastating. However, in modern times the ramifications of equine influenza are most clear in the modern racing industry.
Equine influenza is characterized by a very high rate of transmission among 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 they usually recover in 2 to 3 weeks.
1872 American outbreak
An epizootic outbreak of equine influenza during 1872 in North America became known as "The Great Epizootic of 1872." The outbreak is known as the "most destructive recorded episode of equine influenza in history." The impact of the outbreak is marked as one of the major contributors to the Panic of 1873 in the United States. The first cases of disease in pasture horses were in the townships of Scarborough, York, and Markham in Ontario, Canada. By October 1, 1872, the first case occurred in Toronto. It took only three days before all the street car horses and major livery-stables were affected. By the middle of the month, Montreal, Detroit, and most of the Dominion of Canada and New England reported cases.
By the start of November Ohio, Massachusetts, and South Carolina were reporting cases. So was Chicago, Illinois. The contagion reached Florida and Louisiana by the end of November and Cuba on December 7. The height of the plague was December 14, when the Mexican government had to supply disease-free horses to the stricken United States. One major factor was that cities were not clean back in those days, which meant that germs spread all that much more quickly (especially through contaminated food and water). The rate of infected horses approached 100%, and mortality rates ranged between 1% and 10%. Many horses were unable to stand in their stalls. Those that could stand coughed violently and were too weak to pull any loads or support riders.
The street railway industry ground to a halt in late 1872. Every aspect of American transportation was affected. Locomotives came to a halt as coal could not be delivered to power them, while fires in many major cities raged unchecked. One fire in Boston destroyed over 700 buildings (November 9-10 of that year). Indeed, many a fireman just stood there helpless and horror-stricken, for lack of any equipment to work with. Even the United States Army Cavalry was reduced to fighting on foot against the Apaches, who likewise found their mounts too sick to do battle. The outbreak forced men to pull wagons by hand; while trains and ships full of cargo sat unloaded, tram cars stood idle and deliveries of basic community essentials were no longer being made. The Great Epizootic of 1872 was also a contributor to the Panic of 1873, which lasted six years; hence, it would be about seven years total before things were restored to normal operation.
2007 Australian outbreak
The continent of Australia had remained free of equine influenza until an outbreak in August 2007. While the virus was successfully contained and Australia has returned to its equine influenza-free status, the outbreak had significant effects to the country's racing industry.