Page 69 - Speedhorse November, 2018

Influenza is spread via nasal secretions during horse to horse contact or coughing when another horse inhales droplets containing the virus.
The horses that tend to get equine influenza are young horses that are co-mingled, such as at horse shows and race tracks
Usually the sick horse will get rid of the virus without help within about a week unless the infection is complicated by opportunistic bacteria. “Because influenza is a virus, antibiot- ics are not effective against it,” says Wilson. “Most of the time, treatment simply consists
of supportive care. The sick horse can be given anti-inflammatory medications to keep the fever down and to keep the horse comfortable so it will continue to eat and drink.”
The horse will usually recover faster if it doesn’t become dehydrated and undernourished.
“If it seems like the horse is getting a second- ary infection, or is at high risk for secondary infection, we may put the horse on antibiotics. Consequences of the influenza virus can be costly because of the effect on a horse’s per- formance,” she says. This may be a significant factor for some owners, since it will be several weeks before the horse is fully recovered.
Complications such as pneumonia will delay recovery and can be a problem, but
the virus itself usually isn’t fatal. “Horses occasionally develop serious complications from influenza, however, that are immune- mediated. The immune system, while trying to kill the virus, starts to recognize parts of its own body as foreign as well, and attacks them. Very rarely, horses may develop immune- mediated myositis, or sometimes myocarditis. These are some of the serious complications that may occur,” says Wilson.
If a pregnant mare becomes ill with influ- enza, the virus generally won’t affect the fetus. Influenza usually doesn’t endanger pregnancy unless the mare is so ill that the inflammation and stress causes her to abort. If you have a pregnant mare, you want to keep her healthy and not allow exposure to other horses that might transmit disease.
RISKS AND RECOVERY
Older horses have likely encountered the virus at some point and may have some natural immunity. “It seems like the natural immunity lasts about a year or so,” says Wilson. “There may be some longer-term effects on the immune system that enable older horses to not be as affected by this virus.”
The horses that tend to get equine influ- enza are young horses that are co-mingled, such as at horse shows and race tracks. Sending youngsters to the track is like sending young children off to school; they pick up every “bug” that’s going around.
“Most horses are not going to die from influ- enza, but because it destroys the cilia in the air passages, it will be awhile before full recovery,”
says Wilson. “It takes about three weeks for the ciliary mechanism to regenerate after the horse is no longer ill. During that time, the horse should continue to be laid off from work.”
If the horse continues to work and exercise or goes back to work too soon, with air turbu- lence in the trachea while breathing hard, there will be no protection from bacteria that may enter the respiratory system and the horse may become very sick. “Our recommendation is for these horses to be off work to allow for recovery. The layoff should be at least one week for every day they had a fever during the disease, with a minimum of three weeks since that’s how long it takes for the muco-ciliary apparatus to heal,” she says. Thus, it can be a costly disease because of time lost in training and competing.
If a pregnant mare becomes ill with influenza, the virus generally won’t affect the fetus unless the mare is so ill that the inflammation and stress causes her to abort.
SPEEDHORSE, November 2018 67
EQUINE HEALTH