Equine influenza is an influenza virus that affects horses. While equine influenza is not usually deadly to healthy horses, it can take more than three months for a horse to recover from a serious infection. This disease of horses is considered very contagious, and it can be difficult to distinguish from other diseases of the equine upper respiratory tract. Since it is a viral disease, equine influenza cannot typically be cured, but vaccines are available to protect horses from infection.
Horse flu is generally caused by one of two common subtypes of influenza A, subtype A1 (H7N7) or subtype A2 (H3N8). A1 influenza strains were once implicated in the development of horse flu, but scientists now believe that A1 influenza strains are extinct. The virus typically spreads via the droplets of mucus that fly from a sick horse's mouth when it coughs.
While not usually deadly to healthy horses, equine influenza still presents an economic hardship for stable owners and horse breeders. Horses infected with equine flu must usually be allowed to rest until their symptoms resolve. Most horses recover from the flu within three or four weeks, but it can take some horses up to 100 days to recover from this infection. During this time, horses can't normally be shown, trained, or raced. Horses with equine flu may also rack up veterinary bills, presenting a further financial hardship to their trainers and keepers.
Equine influenza is considered a highly contagious viral disease. Horses are generally considered at the highest risk when they are between one and five years of age, especially if they are exposed to other horses at horse shows, races, or other public events. Other horses at these events may not be vaccinated and may be capable of spreading the flu to unvaccinated animals. Even horses who have been previously vaccinated against equine flu may contract the disease, due to the constantly mutating nature of the influenza virus that causes it.
Symptoms of horse flu are generally limited to the upper respiratory tract. Horses with flu usually cough and may run a fever. Clear mucus may drip from the nose of a horse with the flu. Other infections and conditions, such as pneumonia, can cause similar symptoms in horses. Owners and trainers of horses are generally advised to seek diagnosis from an equine veterinarian, since these other conditions are often far more dangerous than equine flu.
Horses diagnosed with equine influenza are, in the absence of complications, usually prescribed rest. One week of rest is usually recommended for each day that the sick horse suffers a fever. Training, showing, and athletic activity are usually discouraged during the rest period.