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Equine influenza creates problems for horses but can be easily prevented

by Wyoming Livestock Roundup

As cold and flu season becomes center stage for humans during the next few months, it is a good time for owners to remember their horses can also use some protection against the equine form of influenza. 

“In horses, we don’t typically see influenza during the summer because it is too warm. The bugs that cause influenza will develop more rapidly during cooler weather,” according to Erin Denney-Jones, DVM of Florida Equine Services in Clermont, Fla. 

Disease concern

The virus, which is highly contagious, has a higher morbidity than mortality. 

“It is easier to spread than to pass away from,” Denney-Jones said. “In cases where horses die from it, it is usually because they develop a secondary infection like pneumonia or septicemia.” 

The key clinical sign is a horse with a snotty nose that seems lethargic. The horse may also have a nasal discharge, show a lack for exercise, seem listless and show no interest in eating. The horse may also have a temperature. 

Equine influenza is diagnosed by taking a swab of the nasal passage. 

Denney-Jones said it is important to diagnose that it is equine influenza because it is hard to distinguish the virus from Rhino nose and herpes, which have similar clinical signs but can be much more serious.

“If the horse develops a fever from influenza, it is recommended that the horse isn’t ridden for a week for each day it has a fever,” she explained. “That is a lot of time off when someone is trying to condition a horse,” she noted.

Minimizing risks

For new horses coming into a location, Denney-Jones recommends putting them in a welcoming barn where they are isolated for one month. 

“It takes 14 to 21 days for most bugs to incubate inside the horse before they are able to transfer from one horse to another,” she said. “The problem with that is when owners go to a show, each horse can’t be housed in a separate barn or stall, so vaccinations become the best line of defense to prevent the spread of Equine influenza.”

The veterinarian said the disease can be spread through nose to nose contact and sharing of water buckets or even grooming equipment. 

“I would recommend using separate rags to wipe off the muzzle and nose of the horse before it enters the show ring,” she said. 


When the horse coughs or snorts, it can spray the bugs up to 35 feet, which can make it difficult to control the spread of the virus. 

“That is why it is so important to get your horse vaccinated,” she stated. 

Horses that are the most susceptible to equine influenza are those that are immune-compromised, like babies whose immune systems haven’t fully developed. Aged horses can also be susceptible if they have an immune-compromised issue from their age. Other horses may also be immune-compromised if they have disease issues like metabolic insufficiency, insulin resistance, recent treatment of wounds or surgery. 

Stress can also make a horse more susceptible. 

“Vaccinating the horse is an inexpensive way to protect it,” Denney-Jones continued.

Vet advice

Denney-Jones also recommended visiting with a veterinarian to determine which vaccine to give the horse. 

Different vaccinations are available, so horse owners will want to give the one that is the most effective for their area, she said. In most cases, the vaccination will need to be given twice a year but possibly more often depending on how much the horse is around other horses and the area the horse lives. 

“There is also an intra-nasal form of the vaccine that does a fantastic job of covering the mucosa of the area that is attacked by the virus,” she explained. “It is given once a year to adult horses and twice a year to babies because they have a compromised immune system.” 

The veterinarian recommends giving the vaccine when the horse is sedated for dentistry work, since it needs to be administered up its nose. 

Vaccine considerations

Denney-Jones said if horse owners are purchasing the influenza vaccine from their farm supply or feed store, they should check the expiration date and examine the vaccine to make sure it doesn’t have foreign material floating around in it. The vaccine should be chilled until it is ready to be used, she cautioned. 

“It may be better to purchase the vaccine from a veterinarian, so there is an accurate record of when the vaccine was given,” Denney-Jones continued. 

Product support

“The veterinarian also can give owners a certificate for an equine immunization support guarantee, which says if the horse comes down with the flu after the vaccination was administered by a veterinarian, all testing of the virus and treatments required will be paid for up to $5,000. The pharmaceutical companies believe they are making a great product, and as long as it is administered by a veterinarian, they will support their product,” she explained. 

Occasionally, horses can have a reaction from the vaccination, and Denney-Jones said the drug company will also pay for treatment for that if the veterinarian is notified about the reaction after they administer the vaccine. 

“Reactions to vaccinations are something the drug company wants to know about so they can make their product as safe as possible, and be able to say there have been no reactions to giving this vaccine,” she explained.

Gayle Smith is a correspondent for the Wyoming Livestock Roundup. Send comments on this article to

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