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Horse Herpes 101
Published 13 days ago in News

Horse Herpes 101

This blog is here to help you understand the essentials of Equine Rhinopneumonitis (yep, that’s the fancy name), without needing a PhD in veterinary science.

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Martina Osmak
Director of Marketing

If you’ve ever heard the term “equine herpesvirus” and immediately pictured something terrifying, you're not totally off base—but you're also not alone. This blog is here to help you understand the essentials of Equine Rhinopneumonitis (yep, that’s the fancy name), without needing a PhD in veterinary science.

Let’s break it down.

What Is It?

Equine rhinopneumonitis (ER) is caused by two strains of herpesvirus that affect horses: EHV-1 and EHV-4. Think of them as close relatives that just happen to cause different kinds of trouble.

  • EHV-1 is the more dangerous sibling. It can cause:

    • Respiratory illness

    • Abortion in pregnant mares

    • Neurological disease (also called EHM: equine herpesvirus myeloencephalopathy)

  • EHV-4 mainly sticks to the respiratory tract. It’s milder and more common, especially in young horses.

Both viruses are highly contagious and hang around in most horse populations worldwide.

How It Spreads

These viruses love close quarters—think barns, trailers, shows. They’re spread through:

  • Nasal discharge (yuck, we know)

  • Coughing or sneezing

  • Aborted fetal tissue or fluids

  • Shared equipment and surfaces

Once a horse catches EHV, it never really gets rid of it. The virus can “go quiet” in the body and come back during stress or illness—just like cold sores in humans.

What to Watch For

In respiratory cases:

  • Fever

  • Nasal discharge

  • Cough

  • Loss of appetite

  • Lethargy

In mares:

  • Sudden, late-term abortion (often with no warning signs)

In neurological cases (EHV-1 only):

  • Wobbly gait

  • Weakness in the hind end

  • Difficulty urinating or defecating

  • In severe cases, paralysis

How It’s Diagnosed

Veterinarians use a mix of tools:

  • PCR testing: Super sensitive test that looks for viral DNA (usually from nasal swabs or fetal tissue)

  • Virus culture: Trying to grow the virus in a lab (more old-school but still useful)

  • Blood tests: These help but aren’t always conclusive since many horses have been exposed before

Can It Be Prevented?

Yes and no.

  • Vaccines exist and can help reduce:

    • The severity of respiratory disease

    • The chance of abortion

  • But they don’t protect against the neurological form of the disease.

Management matters just as much as vaccines:

  • Quarantine new arrivals

  • Isolate sick horses

  • Clean equipment regularly

  • Avoid overcrowding

  • Minimize stress, especially in pregnant mares

Why the Neuro Version Is So Scary

The neurological form (EHM) is unpredictable and fast-moving. A mutation in the EHV-1 virus can make it more likely to invade the nervous system, but even non-mutated strains can cause problems.

And while it's not super common, when it strikes—it strikes hard.

How Vets Confirm It’s EHV

  1. Nasal swabs or tissue samples (especially in abortion cases)

  2. Blood tests to detect immune response

  3. Post-mortem examination in severe cases

  4. PCR tests for rapid, specific diagnosis

The Bottom Line

EHV-1 and EHV-4 are part of horse life. You can’t eliminate the risk completely, but you can prepare:

  • Vaccinate regularly

  • Keep your biosecurity game strong

  • Act fast when symptoms appear

  • Know your horses' normal behavior so you can spot changes early

Pro Tip for Horse Owners

Just because a horse looks healthy doesn’t mean it can’t spread the virus. That's why biosecurity isn't just for show barns or racing stables—it’s for everyone.

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