Understanding Equine Herpesvirus: Risks, Symptoms, Prevention, and Management

Equine Herpesvirus (EHV) is one of the most significant infectious disease threats facing modern horse management. Highly contagious and capable of producing respiratory disease, reproductive losses, and severe neurological complications, EHV demands careful attention from horse owners, trainers, veterinarians, and equine facility managers. Although the virus is widespread and often carried silently by horses, effective prevention and rapid response strategies can dramatically reduce the risk of serious outbreaks.

This article provides a detailed overview of what EHV is, how it behaves, how it spreads, what clinical signs to watch for, and how to protect equine populations through sound management and biosecurity.

1. What Is Equine Herpesvirus?

Equine Herpesviruses are a family of DNA viruses that infect horses and can also affect donkeys, mules, and zebras. Nine types have been identified, but three of them—EHV-1, EHV-3, and EHV-4—cause nearly all significant disease in domestic horses.

EHV-1

• Most clinically important subtype

• Causes respiratory disease, abortion storms in pregnant mares, neonatal foal death, and Equine Herpesvirus Myeloencephalopathy (EHM)—a serious neurological condition

EHV-3

• Transmitted through breeding

• Causes coital exanthema, a venereally transmitted disease affecting the external genitalia

EHV-4

• Primarily produces respiratory disease, especially in young horses

• Can occasionally cause abortion or neurological disease, though less commonly than EHV-1

EHV does not pose a risk to humans.

2. How the Virus Spreads

EHV spreads readily from horse to horse through multiple pathways:

Direct horse-to-horse contact

• Nose-to-nose interactions

• Shared respiratory droplets (coughing or snorting)

Indirect transmission

• Shared equipment such as:

  • Buckets and feeders

  • Tack and grooming tools

  • Lead ropes, halters, twitches

  • Farrier tools and handling equipment

• Contaminated hands, clothing, and footwear of handlers

Reproductive transmission

• Specific to EHV-3

• Spread during natural breeding or contaminated breeding equipment

Latent infection

One of the most challenging aspects of EHV is its ability to become latent. Horses infected earlier in life can harbor the virus without showing symptoms. During periods of stress—transportation, training, illness, foaling, or social changes—the virus can reactivate, leading to new shedding and transmission.

3. Clinical Signs of EHV Infection

The symptoms vary depending on which form of the virus is involved and the horse’s immune response.

Respiratory Form

Most commonly associated with EHV-1 and EHV-4:

• Fever (often the first sign)

• Nasal discharge

• Cough

• Swollen lymph nodes

• Lethargy and reduced appetite

Reproductive Form

Typically caused by EHV-1:

• Abortion, often late-term

• Stillbirths

• Weak neonates that fail to thrive

This form can occur as isolated events or devastating “abortion storms” in breeding barns.

Neurological Form (EHM)

The most severe and feared manifestation of EHV-1:

• Ataxia (hind-limb incoordination)

• Loss of balance

• Weakness or inability to stand

• Tail paralysis and poor tail tone

• Urinary incontinence or retention

• Head tilt or abnormal posture

• Complete recumbency

EHM cases require urgent veterinary care and strict isolation, as the neurological strain can spread rapidly within a barn.

4. Diagnosis and Veterinary Evaluation

Veterinarians diagnose EHV through:

• PCR testing of nasal swabs

• Blood samples for active or latent infection

• Evaluation of aborted fetuses or placental tissues

• Clinical history of exposure and symptoms

PCR testing is the most definitive and rapid method, especially during outbreaks.

5. Treatment and Clinical Management

There is no cure for EHV, but supportive care is the cornerstone of treatment.

Supportive therapies

• Anti-inflammatory medications for fever and discomfort

• Intravenous fluids for dehydrated horses

• Nursing care for neurologic cases

• Catheterization or bladder management when urinary retention occurs

• Sling support for horses that can stand but are weak

Antiviral medications may be employed in certain situations, though their effectiveness varies.

Neurological cases require intensive supervision and often benefit from hospitalization or specialized care.

6. Prevention and Biosecurity Strategies

Preventing EHV centers on reducing exposure risk, controlling viral spread, and supporting strong immunity.

Vaccination

Vaccines are widely used for:

• Reducing respiratory disease

• Decreasing viral shedding

• Preventing abortion caused by EHV-1

However, no vaccine has proven effective at preventing EHM, the neurological form.

Vaccination remains a valuable tool but must be paired with strong management practices.

Isolation Protocols

• New arrivals or returning horses should be isolated for at least 21 days

• Pregnant mares should be kept separate from transient horses

• Sick horses must be quarantined immediately

Biosecurity Measures

• Do not share equipment between horses whenever possible

• Clean and disinfect water buckets, feeders, tack, and stall tools

• Handlers should wash hands and change outerwear between horses

• Limit barn traffic during disease events

• Monitor temperatures daily during outbreaks or after travel

Event and Travel Precautions

• Avoid nose-to-nose contact at shows

• Bring personal buckets, hoses, and equipment

• Disinfect stalls at event facilities before use

• Monitor temperatures for two weeks after returning home

7. Managing an Outbreak

When EHV is suspected in a barn, swift action is crucial:

• Contact a veterinarian immediately

• Restrict all horse movement on and off the property

• Isolate sick horses and temperature-positive horses

• Implement strict cleaning and handling protocols

• Communicate transparently with staff, owners, and event managers

Most states require veterinarians to report EHM cases to animal health authorities, allowing for coordinated disease control.

8. Long-Term Outlook and Industry Impact

EHV will likely remain an ongoing challenge due to:

• Its ability to become latent

• Wide distribution in equine populations

• Stress-related reactivation

• High mobility of competition horses

However, improved awareness, stronger biosecurity, and rapid response strategies have dramatically reduced the large-scale outbreaks seen in past decades. Continued education and management vigilance are essential.

Conclusion

Equine Herpesvirus is a complex and persistent threat, capable of affecting respiratory, reproductive, and neurological systems. While the virus cannot be eliminated from equine populations, thoughtful prevention, early detection, and decisive outbreak management greatly reduce the risks.

Whether you manage a breeding facility, operate a boarding barn, travel for competition, or care for an individual horse, a proactive approach to EHV is one of the most important components of responsible equine stewardship.

FAQs: Equine Herpesvirus (EHV) for Horse Owners

1. What is Equine Herpesvirus and which types matter most?

Equine Herpesvirus (EHV) is a family of horse-specific DNA viruses. The types that cause most serious disease in domestic horses are EHV-1, EHV-3, and EHV-4. EHV-1 is linked with respiratory disease, abortion, neonatal death, and neurologic disease (EHM); EHV-3 causes coital exanthema; and EHV-4 is mainly a respiratory pathogen, especially in young horses.

2. Can people or other pets catch EHV from horses?

No. EHV is considered a species-specific virus that infects equids (horses, donkeys, mules, and related species). Current evidence does not support EHV as a zoonotic disease, so people and common companion animals like dogs and cats are not at risk of catching EHV from horses.

3. How does EHV usually spread between horses?

EHV spreads mainly through respiratory secretions—nose-to-nose contact and shared droplets from coughing or snorting. It also moves via fomites, such as shared buckets, tack, grooming tools, stall tools, and contaminated hands, clothing, and footwear. During an outbreak, keeping horses from direct contact and assigning dedicated equipment to each group is critical.

4. What are the early warning signs I should watch for?

Early EHV signs often start with fever, sometimes before obvious respiratory changes. Common clinical signs include fever, nasal discharge, cough, enlarged lymph nodes, dullness, and reduced appetite. In some horses, especially with EHV-1, disease can progress to abortion in pregnant mares or neurological signs such as hind-limb incoordination, weakness, loss of tail tone, or difficulty urinating.

5. Is there a cure for EHV, and how is it treated?

There is no antiviral cure that eliminates EHV from the body. Treatment focuses on supportive care, such as anti-inflammatory medications, fluids for dehydrated horses, nursing care, and intensive management for neurologic cases (including bladder support or slings when appropriate). Antiviral drugs may be used in select situations under specialist guidance, but they do not replace isolation and strong biosecurity.

6. Does vaccination prevent EHV outbreaks?

Vaccination against EHV-1/4 helps reduce respiratory disease, abortion risk, and viral shedding, and is widely recommended as part of a risk-based vaccination program. However, current vaccines do not reliably prevent the neurologic form (EHM), and immunity is relatively short-lived, so boosters are needed in higher-risk horses. Vaccination must always be paired with quarantine, hygiene, and temperature monitoring to truly reduce outbreak risk.

7. What should I do if I suspect EHV in my barn?

If you see compatible signs—especially fever clusters, respiratory disease, abortion, or neurologic changes—call your veterinarian immediately and hold all horse movement on and off the property. Start twice-daily temperature checks, isolate sick or febrile horses, and tighten cleaning and handling protocols while your vet coordinates testing (typically PCR on nasal swabs and appropriate samples). Many regions require official reporting for EHM, so your vet will also help you meet regulatory requirements.

8. How long should I monitor temperatures and isolate after travel or an outbreak?

After travel to shows or sales, a common recommendation is to monitor temperatures once or twice daily for 10–14 days and limit nose-to-nose contact during that window. After a confirmed EHV outbreak, barns typically maintain quarantine and daily temperature logs for 21–28 days from the last new case, guided by local animal-health authorities and the attending veterinarian. The exact duration should follow current guidelines and your vet’s advice for your specific situation.