Equine flu (influenza) is similar in appearance to flu in humans. Clinical signs are caused by infection of the respiratory tract and include a dry, hacking cough, runny nose, watery eyes, coughing and fever. It is caused by a highly contagious virus and, while it does not normally cause long term illness, it will lead to your horse requiring time off from work and it can lead to serious complications in very young or old horses.
Typically equine influenza occurs in sporadic outbreaks of horses after the introduction of a carrier animal. Carrier animals shed virus but do not otherwise show clinical signs.
Although the virus is very infectious it only infrequently results in mortality. In severe cases the virus affects other areas of the body including the lungs, heart and gastrointestinal tract. Secondary infection by bacteria can result in more severe respiratory signs and sinusitis. In rare cases the virus has caused neurological disease.
There is no specific treatment for equine influenza and although antibiotics may be useful to control a secondary bacterial involvement they will not treat the virus itself. The only method of active control of the virus is by ensuring routine vaccination.