A multi-state outbreak of Equine Herpesvirus-1 (EHV-1), including several confirmed cases of the neurologic form (EHM), has recently been reported across multiple show and boarding facilities in the U.S. The virus spreads rapidly anywhere horses gather: shows, rodeos, trail rides, training barns, and even during transport.

To ensure this guide reflects the most accurate, up-to-date information, we updated it with insights from Dr. Freya Stein (McKinlay & Peters Equine Hospital) and Dr. Linda Hagerman (Tacoma Equine Hospital), along with current guidance from the American Association of Equine Practitioners (AAEP) and the Equine Disease Communication Center (EDCC).

According to AAEP and EDCC, EHV-1:

• Spreads primarily through nose-to-nose contact, shared water, tack, hands, clothing, and contaminated surfaces

• Can survive on surfaces for up to 7 days (longer in cool, moist conditions)

• May be shed by horses before showing symptoms, creating silent exposure at events

• Requires 21–28 days of quarantine after last known exposure

• Has vaccination options that reduce respiratory disease, though none prevent the neurologic form (EHM)

If your horse has traveled, been near new horses, or attended a show recently:

• Take temperatures twice daily

• Isolate immediately for any fever ≥ 101.5°F

• Keep returning horses separated from home horses for 7–14 days minimum

This updated guide below covers the major viral and bacterial diseases that threaten horses, including the newly heightened EHV-1 concern, and offers updated biosecurity recommendations for anyone hauling horses.

Top Horse Respiratory Diseases to Watch For

1. Equine Herpesvirus (EHV-1 & EHV-4)

(Major update: heightened 2025 outbreak activity)

EHV-1 is one of the most contagious equine viruses. It spreads through:

• Aerosolized respiratory droplets

• Contaminated equipment

• Shared stalls, trailers, buckets

• Human hands, clothing, footwear

Symptoms include:

• Fever

• Lethargy

• Cough or nasal discharge

• Hind-end weakness

• Wobbliness / ataxia

• Inability to urinate normally

The neurologic form (EHM) can appear suddenly and requires immediate veterinary care.

2. Equine Influenza Virus (EIV)

Still one of the most common respiratory infections in horses and the cause of multiple barn shutdowns each year.

Symptoms:

• Fever

• Harsh, dry cough

• Nasal discharge

• Depression / decreased appetite

Vaccination remains the best protection, though breakthrough infections do occur in high-exposure environments.

Dr. Hagerman explains: “Boosting immunity with vaccination is recommended to limit the risk of infection, but immunity takes time to develop. We recommend limiting exposure to other horses during any outbreak period.”

3. Strangles (Streptococcus equi)

A bacterial infection that spreads rapidly, causing:

• Fever

• Thick nasal discharge

• Swollen lymph nodes (“strangles”)

• Difficulty breathing or swallowing

Strangles can shut down an entire barn or showground for weeks.

Other Significant Infectious Diseases

Rabies

Uncommon but always fatal. Horses can transmit rabies to humans.
AAEP strongly recommends annual vaccination.

Tetanus

Enters through wounds or hoof abscesses.
Causes severe muscle rigidity and is often fatal without treatment.
Annual vaccination is essential.

Neurological Viral Diseases

These mosquito-borne infections remain a threat in many U.S. regions:

• West Nile Virus (WNV)

• Eastern Equine Encephalitis (EEE)

• Western Equine Encephalitis (WEE)

EEE carries an extremely high fatality rate. Vaccination is strongly recommended by AAEP nationwide.

Pigeon Fever (Corynebacterium pseudotuberculosis)

Increasing in southern and western states. Transmitted through flies; forms painful abscesses along the chest and abdomen. No vaccine currently exists.

Biosecurity When Traveling With Your Horse Trailer 

Travel remains one of the highest-risk activities for spreading viruses... especially EHV-1.

AAEP, EDCC, and USDA recommend:

1. Use your own buckets, hay bags, and equipment

Never let hoses or communal spigots touch your buckets.

2. Disinfect your trailer after each trip

Focus on:

• Divider latches

• Ramps

• Chest bars

• Tie rings

• Mats
  **A 10% bleach solution or accelerated hydrogen peroxide works well.

Disclaimer: Hauling during an outbreak is not recommended. If travel cannot be avoided, a reverse-loading trailer such as the SafeTack Reverse can help limit nose-to-nose interaction between horses.

3. Avoid tying your horse nose-to-nose with others

Risk is extremely high during any outbreak.

4. Temperature check after every trip

Take rectal temperatures for 7 days post-travel.

5. Limit shared handling

Handlers should avoid touching multiple horses without washing hands.

6. Quarantine after big events

If attending shows or rodeos:

• Isolate returning horses for 7–14 days

• Monitor for fever

• Avoid shared pastures and fences

As Dr. Stein cautioned: “Surfaces contaminated with respiratory droplets, trailer doors, latches, chest bars, even your own hands, can spread viruses between horses if not disinfected properly.”

How to Know If Your Horse Is Sick

(Updated for EHV-1 outbreak relevance)

Call your veterinarian if you see:

• Fever over 101.5°F

• Nasal discharge (any color)

• Cough

• Sudden hind-end weakness

• Wobbliness or stumbling

• Change in behavior

• Swollen lymph nodes

• Reduced appetite

• Diarrhea or reduced manure

• Inability to rise

EHV-1 cases often start with a fever, so temperature monitoring is critical.

“Owners should be comfortable taking a rectal temperature on their horse,” Dr. Stein notes. “Often horses lose their appetites when they have fevers, but not always. Daily temperature checks are one of the best early warning signs we have.”

Resources to Track Outbreaks

These are the most trusted, real-time disease sources:

• EDCC Outbreak Map:
  https://www.equinediseasecc.org/alerts

• AAEP Infectious Disease Guidelines:
  https://aaep.org/guidelines/infectious-disease-control/using-guidelines

• AAEP Vaccine Guidelines:
  https://aaep.org/guidelines/vaccination-guidelines

Frequently Asked Questions About EHV-1 and Horse Disease Prevention

How long does EHV-1 live on surfaces?
EHV-1 can survive up to 7 days on surfaces, and longer in cool, damp environments. Disinfect trailers, tack, and barns after every trip during outbreaks.

Can horses spread EHV-1 before showing symptoms?
Yes. Horses may shed the virus before any fever or respiratory signs appear. This is why twice-daily temperature monitoring is essential.

Does the EHV-1 vaccine prevent the neurologic form (EHM)?
No. Vaccines help reduce respiratory disease and viral shedding, but do not prevent the neurologic form of EHV-1.

Is EHV-1 contagious between horses on the trailer?
Yes. Shared air, surfaces, hay bags, tie rings, and handlers can spread the virus. Disinfecting your horse trailer is a key biosecurity step.

How long should I quarantine my horse after an event?
AAEP recommends 7–14 days for returning horses and 21–28 days for confirmed exposure. Monitor temperatures twice daily.

What is the first sign of EHV-1 infection?
Fever is usually the earliest indicator. Any fever above 101.5°F should be treated as a potential infectious disease warning sign.

About the Veterinarians

Dr. Linda Hagerman: Tacoma Equine Hospital is an independently owned practice that has been serving the South Puget Sound equine community for over 35 years, 20 of those under the current ownership of Dr. Linda Hagerman.  They are dedicated to partnering with horse enthusiasts to provide comprehensive, personalized veterinary care for equids of all ages and disciplines.  Offering routine preventative care, 24/7 emergency services, sports medicine, reproduction, chiropractic, elective surgery, and more: www.tacomaequine.com

Dr. Freya Stein: Dr. Stein works with the McKinlay & Peters Equine Hospital which has 27 years of providing complete and compassionate care. Their team of doctors has over 100 years of combined experience in equine veterinary medicine at two different locations. They offer specialized services from a board-certified Internal Medicine specialist (Dr. Freya Stein) and a residency trained surgeon (Dr. Alyssa Doering), as well as hospital services including intensive care, endoscopy, elective and emergency surgery, advanced dental procedures, and reproductive services. They also have an intern program in its fourth year of operation, which provides diverse and intensive training to early-career veterinarians wanting to focus on equine practice. Learn more at: mckinlaypetersequine.com