Equine influenza can significantly impact your horse's health. Beyond causing discomfort and illness, an outbreak can sideline your horse from competitions and events—disrupting training schedules and competitive goals. While some horses may carry the equine influenza virus without exhibiting symptoms, others can experience a range of effects from mild lethargy to severe respiratory distress. Knowing how to properly care for your infected horse can ensure their swift and complete recovery.
Equine influenza is a respiratory infection caused by strains of the influenza A virus that are adapted to horses. Equine influenza is primarily caused by two subtypes of the influenza A virus, identified by the proteins hemagglutinin (H) and neuraminidase (N) on its surface. Hemagglutinin (H) helps the virus attach to and enter your horse’s cells, while neuraminidase (N) enables it to spread to other horses. The most common cause of equine influenza outbreaks is the H3N8 subtype.
The equine influenza virus is notorious for its ability to mutate and evolve. In fact, there are 198 possible combinations of H and N subtypes, made from 18 different “H” subtypes and 11 “N” subtypes. Through a process called antigenic drift, genetic changes accumulate over time, sometimes leading to new strains that evade your horse's immune system. Since your horse’s immune system does not recognize the traits of these new strains, they can lead to more severe illness or even become fatal. These gradual genetic changes have led to specific strains of equine influenza that now commonly affect horses in the United States and Europe. Currently, New Zealand and Iceland do not have equine influenza.
Yes, equine influenza is highly contagious and can spread rapidly, primarily through respiratory droplets when an infected horse coughs, sneezes, or even exhales. Infected horses can shed the virus for up to 14 days, and a single cough can propel the virus up to 150 feet, facilitating swift transmission among nearby horses, especially in environments where horses are housed together. Implementing strict biosecurity measures—such as handwashing, disinfecting, wearing personal protective equipment (PPE), modifying delivery protocols and more—can also help contain the spread during an outbreak.
Horses can contract equine influenza from a variety of sources and situations, such as:
The virus tends to be more prevalent during colder months. Additionally, horses recovering from equine influenza are susceptible to secondary infections, such as bacterial pneumonia, particularly within the first few weeks post-infection.
Early detection of equine influenza can mitigate its impact and prevent further spread. After your horse is exposed to the virus, you will likely notice symptoms 3-5 days later. The worst symptoms usually last a few days. Horses with a mild case of equine influenza will recover from their illness within a few weeks.
Younger horses, aged 1-5 years old, are most vulnerable to infection with the virus. Additionally, horses whose training or traveling schedules suppress their immune systems are more susceptible to equine influenza. Even if your horse does not have a high risk, you should keep an eye out for these common equine influenza symptoms:
Very severe cases of equine influenza, though rare, could result in impaired heart function (cardiomyopathy) or lower leg swelling (distal limb edema). If your horse exhibits any of these equine influenza symptoms, you should consult with your veterinarian as soon as possible for a diagnosis and treatment plan.
Currently, there is no specific antiviral treatment for equine influenza. However, with appropriate supportive care, rest and a treatment plan from their veterinarians, most horses recover fully. Your veterinarian will likely confirm the presence of the virus by testing a swab from your horse’s nose or throat, known as a RT-PCR array test that detects and measures equine influenza. Other diagnostic tests might include viral isolation, rapid tests or serology.
Your veterinarian may recommend these treatments:
During your horse’s recovery, offering proper care and attention can improve their well-being and reduce the risk of secondary infections. Plus, there are proactive measures you can take to prevent future infections or stop the virus from spreading.
Give your horse plenty of time to rest and recover. A general guideline is to allow one week of rest for each day your horse has a fever, giving their respiratory system enough time to heal. For most cases of equine influenza, you should give your horse at least three weeks for rest after recovering. In severe cases, extended rest periods of up to six months may be necessary.
Preventative vaccination is the most effective strategy against equine influenza. Collaborate with your veterinarian to establish a vaccination schedule aligned with the American Association of Equine Practitioners (AAEP) recommendations. If your horse does still contract the virus, the vaccination often results in milder symptoms and shorter virus shedding periods.
Consider regularly monitoring your horse's temperature to detect early signs of illness. If your horse is recovering from equine influenza, you should vigilantly watch your horse to see whether symptoms change or worsen. This could indicate more severe illness or the development of a secondary infection, both of which could require medication.
To prevent the spread of the virus, isolate your infected horses from healthy ones. Similarly, any new horses arriving at your barn should undergo a quarantine period to ensure they’re not carriers of the virus.
Proper nutrition can support your horse's immune system during recovery from equine influenza. Providing high-quality hay, such as alfalfa, can supply your horse with the necessary nutrients, protein and energy they need. Plus, make sure your hose has access to fresh, clean water at all times.
We understand the challenges of managing equine influenza and are committed to supporting your horse's health. Our equine pharmacy offers both branded and generic medications to help alleviate equine influenza symptoms and potential secondary conditions. Plus, Mixlab offers compounded antibiotics that suit your horse's preferences and needs. All medications include free, two-day delivery. Submit your prescription online or reach out to our team for help.