EHV-1 in Horses: What Horse Owners Need to Know and How to Support Immune Health

Twenty Four Carrots
5 days ago
5 min read

Equine Herpesvirus Type 1 (EHV-1) is one of the most talked-about equine diseases, and one of the most misunderstood. When EHV-1 outbreaks occur, they often bring fear, misinformation, and confusion to barns and horse communities. While EHV-1 is a serious and potentially life-threatening virus, understanding how it spreads, how to recognize early symptoms, and how to support your horse’s immune system can significantly reduce risk.

With today’s increased travel between barns, horse shows, training facilities, and breeding operations, EHV-1 in horses has become a critical topic for responsible horse owners. At Twenty Four Carrots, we believe good horsemanship starts with education, prevention, and proactive care. Informed owners create safer barns and calm, prepared communities protect horses best.

What Is EHV-1 in Horses?

Equine Herpesvirus Type 1 (EHV-1) is a highly contagious viral disease that affects horses of all ages, breeds, and disciplines. It belongs to the Herpesviridae family, a group of viruses known for their ability to remain dormant in the body after infection.

Most horses are exposed to EHV-1 at some point in their lives, often when they are young. In many cases, infection causes mild respiratory illness or no noticeable symptoms at all. However, certain strains of EHV-1 can lead to severe disease, including abortion in pregnant mares and neurological disease known as Equine Herpesvirus Myeloencephalopathy (EHM).

The severity of EHV-1 symptoms depends on several factors:

The strain of the virus
The horse’s immune health
Stress levels and recent travel
Age and reproductive status
Viral exposure level

This variability explains why one horse may experience only a fever while another develops serious neurological signs during the same outbreak.

Types of EHV-1 in Horses

EHV-1 presents in three primary clinical forms. A horse may show one or multiple forms at the same time.

Respiratory EHV-1

The respiratory form is the most common type of EHV-1, especially in young horses or horses exposed to new environments.

Common respiratory EHV-1 symptoms include:

Fever (often the first sign)
Nasal discharge
Cough
Lethargy
Decreased appetite
Swollen lymph nodes

Even mild respiratory cases can shed large amounts of virus, making this form a major contributor to the spread of EHV-1 in barns and at horse shows.

Neurological EHV-1 (EHM)

Neurological EHV-1, also called Equine Herpesvirus Myeloencephalopathy, occurs when the virus damages blood vessels in the brain and spinal cord. This reduces blood flow and causes inflammation, leading to neurological dysfunction.

Neurological EHV-1 symptoms may include:

Hind-end weakness or incoordination
Difficulty standing or rising
Loss of tail tone
Urinary incontinence
Partial or complete paralysis

EHM is considered a veterinary emergency. Immediate isolation and veterinary care are essential to protect the affected horse and others in the facility.

Reproductive EHV-1

EHV-1 is one of the leading causes of late-term abortion in pregnant mares.

Reproductive EHV-1 signs include:

Sudden abortion, often in the final trimester
Little or no warning signs in the mare
High risk of virus spread through fetal fluids and tissues

Because mares may appear healthy prior to abortion, strict biosecurity is essential on breeding farms.

Why EHV-1 Is So Difficult to Control: Latency

One of the most challenging aspects of EHV-1 in horses is viral latency. After initial infection, EHV-1 can remain dormant within the horse’s nervous system or lymphatic tissue for months or even years.

During latency:

The horse shows no clinical signs
The virus is not actively shed

Stress—such as transport, illness, intense training, weaning, or environmental changes—can reactivate the virus. Reactivated horses may shed EHV-1 even without appearing sick, which is why outbreaks can occur unexpectedly in well-managed barns.

How EHV-1 Spreads Between Horses

EHV-1 spreads easily, especially in environments where horses share space and equipment.

Common routes of EHV-1 transmission include:

Direct horse-to-horse contact
Nasal secretions and respiratory droplets
Shared water buckets, tack, and grooming tools
Human hands, clothing, and footwear

Horses that travel frequently to shows, clinics, sales, or new facilities are at increased risk, particularly when travel stress compromises immune function.

Early Signs of EHV-1: When to Call Your Veterinarian

Early detection is one of the most effective ways to limit EHV-1 spread.

Contact your veterinarian immediately if your horse shows:

Fever
Sudden lethargy
Reduced appetite
Nasal discharge
Cough
Hind-end weakness or incoordination

Daily temperature monitoring during outbreaks or after travel is a simple, evidence-based tool that helps identify infection early.

Preventing EHV-1 in Horses

While no prevention plan is 100% effective, strong management significantly reduces EHV-1 risk.

Key EHV-1 Prevention Strategies

Vaccination: Helps reduce viral shedding and severity of respiratory and reproductive disease.
Biosecurity: Do not share equipment between horses.
Quarantine: Isolate new or returning horses for 14–21 days.
Temperature Monitoring: Check daily during outbreaks or after travel.
Stress Reduction: Minimize unnecessary stress that can weaken immunity.

Supporting Your Horse’s Immune System Against EHV-1

While nutrition cannot prevent EHV-1 exposure, it plays a crucial role in immune resilience and recovery.

Balanced Nutrition

A healthy immune system depends on adequate:

Protein and amino acids
Vitamin E
Selenium
Zinc
Copper

Deficiencies in these nutrients can impair immune response and antibody production.

Digestive Health and Immunity

Approximately 70% of the immune system is associated with the gut. High-quality forage, consistent feeding routines, and gradual dietary changes help maintain a healthy gut microbiome, which supports immune regulation.

Antioxidant Support

Illness, travel, and heavy work increase oxidative stress. Antioxidants help protect immune cells from damage and support recovery during immune challenges.

Stress Management

Chronic stress suppresses immune function. Turnout, social interaction, hydration, routine, and appropriate workloads all support immune health.

Nutrition as Part of an EHV-1 Management Plan

At Twenty Four Carrots, we view nutrition as the foundation of long-term equine wellness, not a quick fix during outbreaks. Thoughtfully formulated feeds and supplements support immune health as part of a complete program that includes veterinary care, biosecurity, and responsible management.

*Always consult your veterinarian before adding supplements, especially during illness or outbreaks.

A Calm, Educated Horse Community Is a Safer One

EHV-1 is serious, but panic does not protect horses. Knowledge, preparation, and consistent management do.

By staying informed, practicing strong biosecurity, and supporting your horse’s immune system year-round, you are helping reduce the risk of EHV-1 and protect the wider equine community.

Healthy horses don’t happen by accident, they are built through intentional care, smart nutrition, and teamwork. It truly takes a village.

References

United States Department of Agriculture, Animal and Plant Health Inspection Service (USDA APHIS). Equine Herpesvirus (EHV-1). 2023.
Equine Disease Communication Center. Equine Herpesvirus (EHV-1) Fact Sheet. 2024.
British Horse Society. Equine Herpes Virus (EHV). 2025.
Cornell University College of Veterinary Medicine. Nasal Immunity and Prevention of EHV-1 Transmission. 2019.
University of California Davis, Center for Equine Health. Equine Herpesvirus Myeloencephalopathy. 2023.
New Mexico State University Extension. Equine Herpesvirus-1 Factsheet. 2022.
Kentucky Equine Research. Immune Function and Nutritional Support in Horses. 2024.
National Animal Health Monitoring System. Equine Health and Management Practices. 2020.