What Is Equine Influenza? What Are the Signs?

Equine influenza is a respiratory virus that can spread rapidly among horses. Younger horses or those with a weakened immune system are most likely to get EIV.  

The main symptoms of equine influenza are localized to the respiratory system. The disease generally takes its course over three days and is very unlikely to be fatal.  

EIV can seem similar to other equine respiratory diseases, such as equine herpesvirus, strangles, or bacterial pneumonia. It’s important to have a veterinarian confirm if your horse has EIV or another illness. 

The clinical signs of influenza in horses are similar to those in humans. Symptoms include: 

• High fever 
• Cough (usually dry sounding) 
• Nasal discharge 
• Lymph node enlargement 
• Lethargy 
• Decreased appetite 

Equine influenza is contagious for seven to 10 days after the initial incubation period of three to five days. Any horse who shows signs of illness should be quarantined for safety. 

Equine influenza is mainly spread through secretions from coughing. A horse’s age, immune system, and stabling arrangement can all play a role in their susceptibility.  

The virus can travel 100 feet or more in the air. Dry, windy conditions have been shown to increase the distance the flu virus can travel.  

In addition, humans can carry infective droplets on their skin or clothing to other horses nearby.  

The following conditions make equine influenza transmission more likely to occur: 

• Immunocompromised horses: Horses can have a compromised immune system from the stress of travel and competing at events, from old age, or from having another infection already present. 
• Horses 1–5 years old: Young horses tend to be more susceptible to the virus due to their underdeveloped immune systems. 
• Unvaccinated horses: Vaccines can help prevent the illness. 
• Poor or crowded stabling conditions: Decreased air quality can worsen the spread of germs. 

Equine influenza is not a medical emergency, but contact your veterinarian for advice if:  

• Your horse’s fever is very high (over 101.5 F) 
• There is risk of spread to other horses 
• You suspect your horse has a more severe equine respiratory disease (such as pneumonia) 

Even if your horse does not need to be seen immediately, your veterinarian will most likely need to examine them in the next 24 hours to confirm that the illness is indeed influenza.  

Your veterinarian will take a swab of your horse’s nasal passages and send the sample out for viral testing to confirm equine influenza. It generally takes one to two days for results to return. 

Treatment consists of supportive care, including rest and hydration, as it’s a virus that will need to “run its course.” Infected horses should be quarantined and proper hygiene should be followed, including washing hands and changing clothes before and after interacting with sick horses. 

Other treatments can include NSAIDs like phenylbutazone and flunixin meglumine to reduce fever. 

To help your horse feel more comfortable while they’re ill with influenza, provide a clean environment with good air quality. Since flu is a respiratory virus, this will allow your horse to breathe easier, and will help with coughing by reducing environmental irritants.  

• Wet or soak hay to reduce dust, and change to a less dusty bedding temporarily if needed. 
• Provide plenty of fresh, cool water to drink. 
• Clean the stall frequently if your horse is being kept inside, as the ammonia buildup from urine can greatly affect air quality.  
• Provide a fan to help cool your horse and reduce flying pests.  
• Cold hose your horse if they have an active fever that has not come down to normal with NSAIDs.

There are some products and supplements you can give your horse that may help with throat irritation and cough, including:   

• Farnam Cough Free Pellets Respiratory Health Horse Supplement 
• Select the Best Equi-Tussin Liquid Horse Respiratory Supplement 
• Finish Line Air Power Cough Relief Respiratory Liquid Horse Supplement 

These supplements are herb- and oil-based and work by soothing throat inflammation, much like a cough drop works for humans. They are not a replacement for veterinary care, but can help relieve symptoms while your horse is on the road to recovery.  

Rest is one of the most important factors in allowing your horse to recover.  

Even after coughing and fever symptoms have resolved, your horse should receive an additional 14–21 days of rest before returning to work. This allows the respiratory tract to fully recover before adding the stress of work back in.  

Vaccinating your horse is the easiest and most effective way to prevent equine influenza. The equine influenza vaccine is risk-based, meaning horses should get the vaccine based on their risk factor.   

Depending on stable environment and travel, you will need to vaccinate your horse every six months to a year.  

• For horses kept in a boarding stable, especially with horses frequently traveling to and from the barn, the vaccine should be given every six months.  
• For horses kept in a closed environment in a private backyard, with travel only occurring for a few months out of the year, the flu vaccine can be given once a year before the planned travel.   

Horses who have been vaccinated still have a low chance of becoming infected with equine influenza; however, the course of the disease is generally less severe.  

Limiting exposure to horses with unknown vaccine status, as well as quarantining any new horses coming into a barn, will also reduce chances of spreading equine influenza.   

What is the prognosis for equine influenza? 

The prognosis for equine influenza is excellent. It’s rarely fatal and rarely causes any long-term effects.  

Can equine influenza affect humans? 

Equine influenza does not affect humans, and only rarely has been found in dogs, cats, and pigs.  

How long is equine influenza contagious? 

EIV is contagious for seven to 10 days after the initial incubation period of three to five days. 

How often should a horse be vaccinated for equine influenza? 

A horse should be vaccinated for equine influenza every six months to a year.