Equine Influenza and Herpesvirus: Fever and Cough Tests

Fever and cough in a horse may come from equine influenza, from equine herpesvirus (EHV-1 or EHV-4), or from other germs such as the strangles bacterium. A nasal swab tested by RT-PCR can help detect the virus, and a registered veterinarian reads the result together with the horse's signs. Call your vet early for any feverish, coughing horse.

Why does a coughing horse need a lab test?

A hot, dull horse with a runny nose and a cough is a common sight in a stable, and many different germs can cause it. The signs alone cannot tell your vet which germ is at work. That matters, because the answer decides who else in the yard is at risk and what to watch for in the coming days. A horse that struggles to breathe, will not eat or cannot stand steadily needs a vet at once, and urgent care should never wait for a lab result.

Respiratory illness moves fast where horses share air, water buckets, brushes and the hands of the same handlers. Until your vet says otherwise, keep a coughing horse apart from the others and give it its own bucket and tools.

What is equine influenza?

Equine influenza is a virus that attacks the airways of horses. It spreads through coughs and droplets in the air, and also on shared equipment and hands. Common signs are fever, a dry cough, a runny nose, tiredness and a poor appetite. It can run quickly through a racing yard or show ground.

RT-PCR, short for real-time PCR, looks for the genetic material of a germ in a sample. The Equine Influenza Virus RT-PCR uses a nasal swab to check whether the influenza virus is present. To protect horses in future, ask your vet about vaccination.

How is equine herpesvirus different?

EHV-1 and EHV-4 are two related herpesviruses. EHV-4 mostly affects the breathing passages. EHV-1 can do the same, but in some horses it goes further: a pregnant mare may lose her foal, a newborn foal may become seriously ill, and a few horses develop nerve signs such as a wobbly walk or weak hind legs.

Herpesviruses have another habit. After an infection they can stay hidden in the body and wake up later, for example when a horse is stressed. So a horse that looks quiet and well can still matter to the others in the yard. The Equine Herpesvirus (EHV-1 & EHV-4) RT-PCR looks for both viruses. Because abortion and nerve signs are serious, your vet may want this test early and may suggest keeping pregnant mares well away from a coughing horse.

How is the swab taken, and why does timing matter?

Your vet takes the swab, because the horse must be held calmly and the swab must go in far enough. A long, thin swab is passed gently along the inside of the nostril towards the back of the nose. A swab that only wipes the front of the nostril may pick up too little virus.

Virus is usually easier to find early in the illness, while the horse is feverish and the nose is running. A sample taken after the horse looks recovered may find nothing even though the horse was infected. The swab goes into the tube or liquid the lab supplies and stays cool. Depending on the signs, your vet may also send a blood sample.

Why is one negative result not final?

RT-PCR can only find what the swab caught. A swab taken late, a swab that missed the right spot, or very little virus on that particular day can all give a negative result in a horse that is truly infected. A negative for influenza also says nothing about herpesvirus or any other cause.

Strangles is another cause worth thinking about. It is a bacterial illness that can also bring fever and nasal discharge, so vets often test for it alongside the viruses. The Strangles (Streptococcus equi) RT-PCR checks a sample for the strangles bacterium. If a first result is negative but the horse is still unwell, your vet may repeat the swab, test for other germs or add blood tests. Keep the horse apart in the meantime.

Can one panel cover all three?

The Horse Fever & Respiratory RT-PCR Panel typically groups the influenza, herpesvirus and strangles RT-PCR tests with a blood count and an SAA test, which is a blood marker of inflammation. The exact list is confirmed when you book. Your vet can still add or drop tests.

Read next

To learn what the method does and what it can find, read What Is RT-PCR in Veterinary Testing?. For a closer look at why a swab can come back clear in a horse that is still unwell, read Why a Negative RT-PCR Result Does Not Always Mean No Infection.

Testing in Bhopal

Horses are usually sampled by their vet, who can bring the swab and blood tube to the lab at C-200, C Sector, Shahpura, Bhopal. Sample collection is free anywhere in Bhopal. Stables in other districts can send samples through their vet by courier or bus parcel. Call or WhatsApp +91 88175 01118, and the lab confirms the method, sample needs and reporting time when you book.