RECOVERY FROM INFLUENZA
When a horse develops equine influenza, one of the earliest and most dramatic signs is a fever. “It may be as high as 106 degrees or higher,” says Katie Wilson, DVM, of the Virginia–Maryland College of Veterinary Medicine. “Because of the fever the horse doesn’t feel good and is lethargic and off feed.” Other signs include a clear nasal discharge, enlarged lymph nodes under the jaw and a dry, harsh cough.
There’s little to be done for a horse with influenza beyond resting him and providing supportive care as the initial illness runs its course, which
ly takes three days or less. Because it’s a virus, antibiotics are not effective,” says Wilson. “The sick horse can be given anti-inflammatory medications to reduce fever and keep him comfortable so he will continue to eat and drink.”
However, the flu can lead to other problems: “The virus destroys the lining of the trachea and its cilia—the tiny hairlike appendages that continually move mucus and debris up out of the airway,” says Wilson. These cilia are one of the primary defensive mechanisms that keep dust and inhaled debris out of a horse’s lungs.
“Destruction of the cilia and epithelium leaves a horse vulnerable to secondary bacterial infection on top of the influenza infection,” says Wilson. “This complication is fairly common, and then the horse may develop a thicker white/yellow nasal discharge and may be sicker and for a longer period of time. The respiratory infection may progress into the lungs [pneumonia], which can sometimes be life-threatening if it is not recognized and treated early. If it seems like the horse is getting a secondary infection, or is at high risk for secondary infection, we may put him on antibiotics.”
To minimize the risk of secondary infections, the horse must be rested well beyond the point when the initial illness passes: “It takes about three weeks for the mucociliary mechanism to regenerate,” says Wilson. “In the meantime, the horse should be laid off from work. The layoff should be at least one week for every day that the horse had a fever during the disease—with a minimum of three weeks.”
The layoff period may be even longer—six months or more—for horses with secondary pneumonia or other complications. More serious effects are rare but they can occur.
“Horses occasionally develop serious complications from influenza that are immunemediated,” says Wilson. “The immune system, while trying to kill the virus, starts to recognize parts of its own body as foreign and attacks them. Very rarely, horses may develop immune-mediated myositis [a muscle disease] or sometimes myocarditis [inflammation of the heart muscle].”