Influenza in horses

The Equine Influenza is a virus (type A, Subtype H3N8) that affects the respiratory tract of the horse. Influenza is a highly contagious disease that can cause severe symptoms in horses. Due to its extreme contagiousness, influenza is included in the basic vaccination schedule.

What are the symptoms of influenza?

Influenza has an incubation period of 1-3 days. During these days, the horse is already contagious but does not show any signs of illness yet. Influenza has several very clear symptoms, namely:

• Very high fever
• Nasal discharge
• Harsh, dry cough
• Loss of appetite
• Swollen lymph nodes
• Muscle pain and overall weakness

In a later stage, the symptoms can change to green/yellow pus-like nasal discharge, phlegm, and severe pneumonia. Often, these symptoms are not caused by the virus itself, but by bacteria taking advantage of the horse's weakened immune system. For foals, the influenza virus can be deadly, but adult horses mainly face problems due to other bacteria and viruses invading and making the horse sicker. This can also lead to death.

What to do if your horse has influenza?

Horses infected with influenza should be isolated to prevent other horses from becoming infected. Caretakers should also take the necessary precautions to prevent further spread of the virus. The virus spreads from animal to animal, but also through people, water troughs, and grooming tools. The respiratory droplets from coughing horses can travel a long distance.

The horses should be given absolute rest and plenty of fresh air. Horses with extremely high fever that stop eating and drinking may benefit from fever reducers. In case of pneumonia (a secondary symptom caused by bacteria), antibiotics may be necessary. Horses recovering from influenza should be given enough time to rest. As a general rule, for every day of fever, at least 1 week of recovery time should be provided. Horses are also more susceptible to other viruses and bacteria for about 50-100 days after infection.

But my horse is vaccinated, shouldn't it be protected against influenza?

If the majority of horses in the area are vaccinated, there is a lower infection pressure and better resistance to the influenza virus. However, with a lowered immune system, the horse can still contract influenza, usually in a milder form. An unvaccinated horse increases the number of virus particles in the group, making the risk of infection higher for vaccinated horses as well.

Do you suspect influenza? Your veterinarian can confirm this by taking a nasal swab. It is important that suspected horses are kept separate from others.