Virtually every species has its own species-specific flu virus. Not only does the horse flu cause the same symptoms as the people flu, but it spreads in a similar fashion. A cough can carry the virus 35 feet. Horses that congregate at racetracks, shows, sales, or even veterinary hospitals are most likely to be exposed to the equine flu virus. In the body, equine influenza infects the ciliated cells that line the respiratory tract.
Cilia are the little arms coming out of a cell.
When viruses destroy the ciliated cells, it's easy for bacteria to take up residence there. Without cilia, bacteria and mucus build up in the airways. Trainers don't like it, but it will take three weeks to repair the cilia. If a horse goes back to work before that, he can have additional problems. Antibiotics won't help the horse get rid of a viral infection, but they may help if a secondary bacterial infection develops.