Equine Rhinitis Viruses (ERAV & ERBV): Transmission, Symptoms & Treatment

Equine rhinitis viruses A and B (ERAV and ERBV) are contagious respiratory viruses that commonly infect horses worldwide. These infections are a frequent cause of mild respiratory illness, particularly in young horses and those housed in group settings such as training barns, breeding farms, and competition facilities.

Affected horses may develop signs such as fever, nasal discharge, coughing, and reduced appetite, although some horses have only very mild signs or no obvious symptoms at all.
While most cases resolve with rest and supportive care, these viruses spread easily through respiratory secretions and contaminated surfaces, allowing outbreaks to move quickly through barns and disrupt training or competition schedules.

Understanding how equine rhinitis viruses spread, recognizing early clinical signs, and implementing effective biosecurity practices are key to limiting transmission and protecting herd health.

Equine Rhinitis Viruses

Equine rhinitis viruses A and B (ERAV and ERBV) are contagious viruses that cause respiratory infections in horses. These viruses are widely distributed in horse populations, and are highly transmissible, which means outbreaks can escalate quickly in group housing settings. ^[1]

Clinical signs can range from mild to moderate respiratory illness. In most cases, illness resolves with minimal intervention, but more pronounced signs may occur in horses under stress or with reduced immune function. ^{[2][3][4][5][6]}

Equine rhinitis viruses spread through respiratory secretions. ^[1] These viruses primarily affect the respiratory tract and can cause symptoms such as fever, coughing, and nasal discharge. The illness caused by these viruses is sometimes compared to the common cold in people, as many infections are mild and resolve with rest and supportive care.

Table 1. Equine rhinitis viruses (ERAV & ERBV) at-a-glance

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Classification & Virology

Equine rhinitis viruses belong to a group of viruses that infect the respiratory tract of horses. Equine rhinitis A virus was first identified in the United Kingdom in 1962, and a second related virus, equine rhinitis B virus, was discovered in 1973. Both viruses are now recognized as causes of respiratory disease in horses. ^[1][2]

Although ERAV and ERBV cause similar symptoms, they belong to different virus groups and have some biological differences. ERAV is part of the Aphthovirus genus, while ERBV belongs to the Erbovirus genus, reflecting differences in their genetic classification and viral characteristics. ^[7][8][9]

Equine Rhinitis A Virus (ERAV)

Equine rhinitis A virus is part of the Aphthovirus genus in the Picornaviridae family, the same virus family that includes foot-and-mouth disease virus. ERAV is a small, non-enveloped RNA virus that can remain stable in the environment for extended periods compared to many other respiratory viruses. ^[7]

This virus primarily infects the upper respiratory tract but can also be associated with fever and inflammation that affects a horse’s overall condition.

Equine Rhinitis B Virus (ERBV)

Equine rhinitis B virus belongs to the Erbovirus genus, also within the Picornaviridae family. Like ERAV, it is a small RNA virus without an outer envelope, which contributes to its ability to persist in the environment and spread between horses. ^[9]

Several subtypes of ERBV have been identified, which distinguishes it from ERAV and may contribute to variation in how the virus circulates within horse populations, although they generally cause similar respiratory symptoms.

ERAV vs. ERBV

Although ERAV and ERBV cause similar clinical signs, ERAV infections are more often associated with fever and systemic illness, while ERBV infections are frequently milder or subclinical. ^[3][5]

Both viruses are widespread and may circulate in horse populations without always causing noticeable disease. Good stable management and biosecurity practices play an important role in limiting transmission.

Table 2. Comparison of ERAV and ERBV

How Common Are ERAV and ERBV?

Equine rhinitis viruses A and B are found in horse populations around the world. Many horses are exposed to these viruses at some point in their lives, and infections often occur in environments where horses are kept in close contact, such as boarding barns, breeding farms, racetracks, and competition facilities.

Exposure to equine rhinitis viruses is very common. By about five years of age, an estimated 60–80% of horses have antibodies for these viruses, indicating they have been exposed to ERAV or ERBV at some point in their lives. ^{[3][6][8][10]}

Young horses are more likely to become infected because they have not yet developed immunity. However, horses of any age can develop equine rhinitis virus infection if they are exposed.

Equine Rhinitis Virus Transmission

ERAV and ERBV are primarily spread through direct contact with infected horses and respiratory secretions from equine rhinitis virus infection. When infected horses cough, sneeze, or have nasal discharge, virus particles can spread to nearby horses. ^[11]

The viruses may also spread indirectly through contaminated equipment, water buckets, feed tubs, tack, or human hands and clothing. Because these viruses can remain stable in the environment for some time, contaminated surfaces can contribute to transmission within barns. ^[10][12]

Infected horses may shed the virus in respiratory secretions and sometimes in urine or feces for a period after infection, which can allow the virus to spread in shared environments. ^[1][6][13]

Horses may begin shedding the virus before showing clear signs of illness, which makes it easier for outbreaks to occur in group housing situations.

Risk Factors

Several factors can increase the risk of ERAV and ERBV infections spreading within a barn, including: ^[3][12]

• Close housing of horses, such as shared barns or paddocks
• Frequent movement of horses between farms, training facilities, or competitions
• Stress, including transportation, intense training, or changes in environment
• Mixing horses from different sources, which may introduce new viruses

These conditions are common in performance and breeding operations, which can allow respiratory viruses to spread quickly.

Symptoms of Equine Rhinitis Viruses

The clinical signs of equine rhinitis virus infection (ERAV or ERBV) range from mild to more noticeable respiratory illness. Some horses develop clear signs of infection, while others show only subtle changes or no obvious symptoms.

After entering the respiratory tract, the viruses infect cells lining the airways and trigger inflammation, which can interfere with normal airway function. Signs of infection typically appear 2–4 days after exposure. ^[14]

Horses infected with ERAV or ERBV may develop signs of respiratory illness that last several days, including: ^{[1][3][6][7][8][15]}

• Fever
• Nasal discharge (clear or cloudy)
• Eye discharge
• Dry coughing
• Lethargy or reduced energy
• Reduced appetite
• Swollen lymph nodes under the jaw

Most infections are mild, particularly in adult horses, and may only cause slight decreases in energy, mild nasal discharge, or occasional coughing. In some cases, horses may develop higher fever and more pronounced respiratory signs that can affect comfort and performance. ^[3][6][16]

When to Call the Veterinarian

The signs of equine rhinitis virus infection can overlap with more serious respiratory conditions, including equine influenza, equine herpesvirus (EHV), and strangles. For this reason, horse owners should not assume that fever, coughing, or nasal discharge are caused by ERAV or ERBV, especially if signs persist or worsen.

Veterinary evaluation is recommended if a horse has:

• Fever
• Persistent or worsening cough
• Nasal discharge that is heavy, prolonged, or accompanied by odor
• Lethargy or reduced appetite lasting more than a few days
• Increased respiratory effort or difficulty breathing
• Clinical signs that do not improve with rest
• Similar symptoms appearing in multiple horses

Prompt veterinary assessment can help rule out more serious infectious disease and guide appropriate management, especially in barns where horses are housed in close contact.

Diagnosis of Equine Rhinitis Viral Infections

Most equine rhinitis virus infections are mild and self-limiting, meaning many cases are not formally diagnosed and the condition is likely underrecognized in horse populations. Confirming the cause of respiratory disease can help veterinarians recommend appropriate management and biosecurity measures to reduce the risk of further spread.

Because the clinical signs overlap with more serious respiratory diseases such as equine influenza, equine herpesvirus (EHV), and strangles, owners may pursue diagnostic testing to rule out these conditions when symptoms are more pronounced or affect multiple horses.

During a veterinary workup, nasal swabs are typically collected from horses showing early signs of illness, when the virus is most likely to be present in respiratory secretions.

Confirming infection typically requires veterinary evaluation and diagnostic testing, such as bloodwork or PCR testing, to identify the virus and distinguish it from other respiratory pathogens. ^[3][17][18]

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Treatment for Equine Rhinitis Virus Infections

There is no specific antiviral treatment for equine rhinitis viruses. Management focuses on supportive care while the horse’s immune system clears the infection.

Most horses recover with basic supportive care, which may include: ^[3][19]

• Rest and reduced exercise
• Monitoring body temperature
• Ensuring access to fresh water and feed
• Keeping the horse in a clean, well-ventilated environment

If a horse develops a high fever or significant discomfort, a veterinarian may recommend anti-inflammatory medications to help reduce fever and relieve pain. ^[3]

Rest is an important part of recovery. Exercise during respiratory illness can delay recovery and increase the risk of complications. For this reason, many veterinarians recommend allowing horses to rest until their fever has resolved and respiratory signs have improved before gradually returning to work.

Prognosis for ERAV & ERBV Infections

The prognosis for horses infected with equine rhinitis viruses is generally good. Most horses recover fully with rest and supportive care.

Clinical signs usually improve within one to two weeks. Horses with mild infections may return to normal behavior relatively quickly once the illness resolves. ^[3][4][19]

In some cases, recovery may take longer, particularly in young horses, horses in heavy training, or animals experiencing stress. Secondary bacterial infections can occasionally develop following viral respiratory disease and may require veterinary treatment. ^[14]

Monitoring a horse’s temperature, appetite, and overall energy level during recovery can help determine when it is safe to gradually return to normal work.

Preventing ERAV & ERBV Transmission Between Horses

Equine rhinitis viruses spread easily between horses, particularly in barns where animals share airspace, equipment, and handlers. Robust biosecurity and stable management practices can help reduce the risk of infection and limit the spread of disease if a case occurs. ^{[3][4][13][19]}

Monitor Horses for Illness

Early detection helps prevent respiratory disease from spreading through a barn. Owners should watch for signs such as:

• Fever
• Coughing
• Nasal discharge
• Lethargy

In addition, some barns monitor rectal temperatures daily, especially after travel or competitions, since fever is often one of the first signs of respiratory infection.

Keeping track of each horse’s baseline and overall health helps ensure signs of contagious illness are identified early, which supports prompt quarantine and veterinary assessment.

Isolate Sick Horses

Horses showing signs of respiratory illness should be separated from healthy horses as soon as possible. Housing sick horses in a separate stall or area and limiting contact with other horses reduces the chance of transmission.

When caring for multiple horses, it is best to handle healthy horses first and sick horses last. Handlers should also wash their hands and change clothing or gloves after contact with horses who have suspected or confirmed contagious disease.

Avoid Sharing Equipment

Respiratory viruses can spread through contaminated equipment and surfaces. Avoid sharing items such as water buckets, feed tubs, grooming tools, or tack between horses.

Regular cleaning and disinfection of equipment, stalls, and frequently touched surfaces can help reduce the spread of infectious agents.

Quarantine New Arrivals

Introducing new horses can increase the risk of bringing respiratory viruses into a barn. Many facilities quarantine new arrivals for one to two weeks to monitor for signs of illness before allowing them to mix with the resident herd. This precaution can help identify potential infections before they spread to other horses.

Maintain Hygiene & Cleanliness

Routine cleaning helps reduce the buildup of infectious agents in the barn environment. Stalls, water buckets, feed tubs, and frequently touched surfaces such as doors, gates, and cross ties should be cleaned regularly. Good ventilation and removing manure and soiled bedding promptly can also help maintain a healthier environment for horses.

Frequently Asked Questions

Here are some frequently asked questions about equine rhinitis viruses:

Summary

Equine rhinitis viruses A and B (ERAV and ERBV) are contagious viruses that cause respiratory infections in horses and are found in horse populations worldwide.

• The viruses spread through respiratory secretions and contaminated equipment, especially in barns where horses are housed closely together
• Common symptoms include fever, nasal discharge, coughing, lethargy, reduced appetite, and swollen lymph nodes under the jaw, although some horses show only mild signs or none at all
• Diagnosis is typically confirmed by a veterinarian using tests such as PCR on nasal swabs or blood tests to detect antibodies
• There is no specific antiviral treatment; most horses recover with rest and supportive care
• Prevention focuses on good biosecurity practices such as isolating sick horses, monitoring temperatures, avoiding shared equipment, quarantining new arrivals, and maintaining regular barn cleaning