You wake up after having a fitful night, coughing, wheezing and constantly grabbing for that next tissue. Your chest feels it's in a vice, you can't eat and you've got the blues. What you really have is the flu, and when your horse has it, he doesn't feel any better.
Influenza is a virus and is very contagious in horses.
The flu in horses is caused by two distinct strains of influenza virus. Symptoms include inflammation of the nasal passages and throat, fever, coughing, wheezing, lack of appetite and depression. Because the flu is a virus, there is little that can be done to cure it, other than to treat the symptoms and increase the comfort level of its victim. However, when your horse also happens to be a competition animal and an excellent athlete, it's difficult to wait for a flu to run its course. Influenza virus infections are common among young horses in training, and outbreaks of the virus occur at least annually in most horse populations.