🐴 Respiratory vs. Neurological Herpes in Horses: Prevention & Detection in 2025 🧠💨

By Dr Duncan Houston BVSc

Equine herpesvirus (EHV-1) is a well-known threat in horse populations. While most cases cause mild respiratory signs, a smaller percentage of horses develop a deadly neurological form of the disease. In 2025, understanding the difference—and knowing when to act—is key to saving lives. 🧠🐎

💨 The Respiratory Form of Herpes

This is the most common form of EHV-1 and usually affects young horses. Signs include:

• 🌡️ Fever
• 💧 Nasal discharge
• 😷 Coughing
• 🥱 Mild lethargy

Most recover uneventfully with supportive care. However, this form can lead to outbreaks and opens the door for more serious complications. 🧪

🧠 The Neurological Form: EHM

The neurological form, known as equine herpesvirus myeloencephalopathy (EHM), is much more serious. It typically affects older horses or mares that are pregnant or nursing. ⚠️

Signs of EHM include:

• 🦵 Hindlimb weakness or incoordination
• 💥 Sudden inability to stand
• 💧 Urinary incontinence or bladder dysfunction
• 🔄 Tail tone loss or stumbling

This form is life-threatening and requires immediate veterinary care. Even with aggressive treatment, many horses do not survive. 🛑

🔬 How the Virus Spreads and Mutates

In both forms, the virus initially enters through the respiratory tract and is picked up by the lymphatic system. From there:

• 🧪 The virus enters the bloodstream (viremia)
• 💥 It infects the blood vessels in the spinal cord and brain
• 🧠 Inflammation and blood clots (vasculitis) cause tissue damage

It’s not fully understood why some horses stop at the respiratory stage and others progress to neurological disease. 🔍

📊 Who’s Most at Risk?

🔺 Risk Factors for EHM:

• 📈 Increasing age
• 🚺 Female sex (especially pregnant or nursing)
• 🐎 Certain breeds: Standardbreds, warmbloods, thoroughbreds, quarter horses, paints, appaloosas, Spanish horses, fjords, drafts, Lipizzaners

Even with these risk factors, only about 10% of horses with herpes develop EHM. 🧬

📉 Fever Pattern Differences

Michigan State researchers found a useful clue:

• 🌡️ Respiratory herpes: Often has two fever spikes
• 🌡️ Neurological herpes: Typically shows only the second fever

Knowing this can help differentiate early in the disease course. 📋

🧪 Current Testing and Vaccination

✅ Testing:

• 🔬 Nasal swab PCR to detect active virus
• 🧫 Blood testing to confirm viremia

✅ Vaccination:

• 💉 Vaccines are available for EHV-1 but do not prevent the neurological form
• 🧠 They do reduce shedding and outbreak severity

🧠 Can We Prevent EHM?

Unfortunately, there’s no guaranteed way to prevent EHM. However:

• 🛡️ Isolation and biosecurity reduce spread
• 📆 Early vaccination helps reduce respiratory outbreaks
• 🧪 Research is ongoing to modify immune responses in at-risk horses

📲 Ask A Vet for Neurological Symptom Review

Not sure if your horse’s signs are viral, neurological, or something else? Visit AskAVet.com or use the Ask A Vet App for fast insight on EHV signs and emergency response. 📱🐴

Dr Duncan Houston and the team can guide you through diagnostic steps, outbreak precautions, and symptom progression to catch EHM early. 💬🧠

🏁 Final Thoughts

Herpes in horses comes in two major forms—respiratory and neurological. In 2025, we’re closer to understanding who’s at risk and how to respond quickly. But when neurological signs appear, time is critical. Monitor fever patterns, isolate affected horses, and don’t delay vet care. 🧬🐎

Need an EHV plan? Visit AskAVet.com to protect your herd and manage risk 🐴💉