Equine Influenza (horse flu) is a highly infectious disease in which the affected animal (horse, donkey, mule or zebra) will have several symptoms including a high fever and a dry cough.
- a high temperature of 39-41deg C (103-106deg F), lasting for one to five days.
- a dry, harsh-sounding cough that may linger for several weeks.
- a clear nasal discharge that may turn green or yellow as secondary infections developed.
- swollen lymph nodes under the jaw
- a clear eye discharge
- depression, lethargy, and loss of appetite.
- there may be swelling in the lower limbs and a horse may be stiff and reluctant to move.
- More detail on symptoms
Blood tests and nasal swabs are necessary for definitive diagnosis, but consistent clinical signs and close proximity to a confirmed property is often enough.
If you suspect your horse has equine flu, stop working him immediately. Continuing to work an affected horse will worsen their respiratory status.
The very young and the very old are most vulnerable. Aged horses and foals aged from one to five months can be affected by pneumonia, which can be fatal.
Keep sick horses out of bad weather and in the shade.
Treatment of equine flu boils down to rest and husbandry. There is no direct means of fighting the virus with drugs, and while anti-influenza compounds are available for use in humans, these have not been used extensively on horses.
Horses should be rested for one week for every week of fever, with a minimum of three week’s rest. A veterinarian may prescribe an anti-inflammatory drug if the horse’s fever is over 40ºC (104F). Antibiotics may be prescribed when the fever lasts for more than three or four days, or when purulent nasal discharge or pneumonia are present.¹
Fresh air and rest are vital. Avoid dust in the environment, bedding and feed (particularly hay) to minimise the risk of bacterial infections of the lungs and airways.
Affected horses should be confined, and walked for short periods to maintain circulation. This should continue for at least the period of the fever and coughing, followed by gradually increasing exercise.
The virus damages the respiratory tract, that is the lung tissue and windpipe. Secondary bacterial infection can result. It takes 30 days for repair of this tissue. For equine athletes, a subsequent 30 days is also advised before starting work again.
A vaccine which induces mucosal (local) antibody protection, has demonstrated protection against natural challenge. The duration of protection is limited so boosters should be administered often; every three to six months.¹
The vaccine virus is shed for up to 10 days after vaccination. Horses that will be going to a competition where testing for equine influenza virus is performed for entry should be kept separate from vaccinated horses for at least two weeks to eliminate the chance of exposure to the vaccine virus.²
Under FEI rules, from 1 January 2005 onward, influenza vaccination for all horses competing in FEI competitions requires a vaccination within six months + 21 days of the competition. Horses competing regularly consequently require twice yearly boosters.³
As at August 2007, two vaccines are registered in New Zealand for emergency use. There are currently no plans to vaccinate horses in New Zealand as a precautionary measure.
Immune stimulants, containing a bacterial extract (Propionibacterium acnes) may shorten the course of viral respiratory diseases and when administered 2 and 5 days before shipping may lessen the incidence of respiratory disease in transported horses.
Adverse reactions may occur after vaccination. These can include:
• A transient swelling (max. diameter 5cm) which regresses within 4 days may appear at the injection site.
• Pain and local hyperthermia can occur in rare cases.
• A slight increase in temperature (max 1.5C) may occur for one (1) day, exceptionally two (2) days.
• In exceptional circumstances, apathy and reduced appetite may be observed the day after vaccination.
• In exceptional circumstances a hypersensitivity reaction may occur, which may require appropriate symptomatic treatment.
Horses should not be worked hard for at least two days after each dose of vaccine.
¹ The Merck Veterinary Manual
³ FEI equine influenza vaccination requierments