Equine Influenza – Can You Ride Your Horse Through a Flu?

A Guide to Equine Influenza – Can You Ride Your Horse Through A Flu?
By: Diane K. Gross – DVM – The Ohio State University

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Equine Influenza – Catching The Flu

A horse catches the flu by inhaling virus particles that become airborne when an infected horse coughs or sneezes. Therefore, to contract influenza, a horse has to be relatively close to an infected horse.

The need for proximity explains why horses that are not exposed to other horses have little risk of coming down with influenza. Outbreaks tend to occur when horses are brought together in large groups and are in close contact, such as at shows, racetracks and inside boarding stables. The more horses you bring together, the higher the odds that one of them will have influenza and can spread it to the others.

Equine Influenza – Can You Ride Your Horse Through a Flu?

You wake up after having a fitful night, coughing, wheezing and constantly grabbing for that next tissue. Your chest feels its in a vice, you can’t eat and you’ve got the blues. What you’ve really got is the flu, and when your horse has it, he doesn’t feel much better.

With many major horse shows and competitions taking place during the next two months, the likelihood your horse will contract the flu, if you’re one of those traveling, is a fairly good one. Influenza is a virus and is highly contagious in horses. In horses, the virus is caused by two distinct strains of influenza virus A. Symptoms include inflammation of the nasal passages and throat, fever, coughing, wheezing, lack of appetite and depression. Because it is a virus, there is little that can be done to cure it, other than to treat the symptoms and increase the comfort level of its victim. However, when your horse also happens to be a competition animal and an excellent athlete, it’s also difficult to wait for a flu to run its course.

Influenza virus infections are common among young horses in training and outbreaks of the virus occur at least annually in most horse populations. In a study conducted at The Ohio State University, under guidelines of the OSU animal care and use committee, to determine the effects of exercise on horses infected with influenza, as compared with infected horses given stall rest, it was concluded that while the exercised horses did not have the virus any longer than those given stall rest, the symptoms were definitely exacerbated by exercise. Exercised horses were worked on a treadmill five days a week at six miles per hour.

In the study, all the horses exhibited signs of the virus with 36 hours of infection, including fever, coughing, nasal discharge, lack of appetite and depression. Those symptoms persisted for 13 days following infection and were more severe in the exercising horses. Fever also developed in all horses and was persistent for 11 days following infection. Pneumonia eventually developed in all horses with the viral infections being more dramatic in the exercised horses. While all horses experienced weight loss within four days of infection, exercised horses lost 40 more pounds than those having stall rest and continued to have lower weights for a month. Exercised horses also appeared to fatigue and have a delayed recovery from exercise.

Obviously, the exercised horses tended to exhibit more severe clinical signs of respiratory disease from the first day of infection until about the ninth day following infection. Clinical signs were resolved in both the exercised horses and those receiving stall rest by the 14th day following infection.

While horses infected with influenza were able to exercise without developing incapacitating disease, and it appears that the exercise did not prolong the affects of the virus, it is important to note that the study did not mimic the adverse conditions which might be encountered in training environments. Horse owners should keep in mind that in keeping their top athletes fit, it is best not to exercise their horses, and if at all, mild to moderate exercise at the maximum, i.e. walking or trotting on a line. Clearly, the effects of the disease will not dissipate any sooner than it normally takes for the virus to run its course.

If your horse contracts influenza, you should be cautious about exercising your horse at all, and stay aware of the signs of distress your horse might exhibit while exercising. Contact your veterinarian regarding methods you can use to prevent influenza in your traveling animal and what you can do to ease him through a couple of weeks of discomfort and misery.

Diane K. Gross, DVM, is currently a PhD candidate at The Ohio State University under the supervision of Paul Morley, DVM, and is presenting her findings of this study during the 1997 AAEP Convention in Phoenix, Arizona. Research will continue in this area.

Influenza Facts

Influenza spreads by air, so horses kept together in enclosed spaces are more susceptible than those kept outdoors.
Foals with no immunity to influenza viruses, and older or sick horses with poor immune responses, are most vulnerable.
Lung damage from influenza can take up to 30 days to completely heal.
Minimizing stress will help your horse’s immune system fight influenza.
If your horse will be traveling or coming into contact with outside horses, consider vaccinating, and discuss the options with your vet.

Equine Influenza Symptoms

Influenza symptoms are similar to any upper respiratory infection-but worse. Symptoms usually appear within three days of initial infection and begin with a high fever (as high as 106), loss of appetite, and a deep, dry cough.

The virus attacks the ciliated cells lining the respiratory tract. Ciliated cells have many small projections, like hairs, on their surface. Their job is to sweep mucus, dust and surface organisms up out of the lung. When these cells are lost, the lungs have no way to clear themselves. They become vulnerable to the virus penetrating the tissues, as well as to secondary bacterial infection.

If a secondary infection does not occur, flu symptoms will usually peak about six days after infection, then begin to resolve. In uncomplicated cases, recovery may appear in about 10 days, but the damage to the lungs can take up to 30 days to completely reverse.

Some strains of equine influenza can invade other tissues, producing joint pain, muscle pain, and swelling of the legs and scrotum. The virus may even invade the heart muscle or cause colic.

Working the horse too soon after a bout of influenza can lead to chronic problems with sinus or throat inflammation, lung irritation (including the development of allergies and hypersensitivities), or heart damage. For this reason, it is always wise to rest a horse for a full 30 days following the onset of symptoms to give the body adequate time to heal.