Bit & Bridle

Equine Rhinitis Virus (ERV)

Other Names

  • Equine Rhinitis Virus (ERV)
  • Equine Rhinovirus
  • ERV-A (Equine Rhinitis A Virus)
  • ERV-B (Equine Rhinitis B Virus)
  • Equine Picornavirus Infection

What is Equine Rhinitis Virus?

Equine Rhinitis Virus (ERV) is a highly contagious viral infection of horses caused by members of the family Picornaviridae. Two main types are recognised: Equine Rhinitis A Virus (ERV-A, formerly known as Equine Rhinovirus 1) and Equine Rhinitis B Virus (ERV-B, formerly Equine Rhinovirus 2 and 3). Both are responsible for upper respiratory tract disease in horses worldwide, though ERV-A tends to produce more severe clinical signs.

The virus primarily affects the mucous membranes of the nasal passages and upper respiratory tract, causing an acute febrile illness with nasal discharge, coughing, and general malaise. While ERV infection is rarely fatal in otherwise healthy adult horses, it is a significant cause of lost training time, particularly in competition horses and racing yards where close contact facilitates rapid spread.

Notably, ERV is one of several causes of “snotty nose” in horses — the non-specific term used by horse owners to describe any upper respiratory discharge — and distinguishing ERV from other respiratory pathogens (equine influenza, equine herpesvirus, equine viral arteritis) requires specific diagnostic testing rather than clinical examination alone.

Causes of Equine Rhinitis Virus

ERV is caused by infection with Equine Rhinitis A or B Virus:

  • Direct transmission: The virus spreads primarily by direct nose-to-nose contact between horses, or via aerosol droplets from coughing and sneezing.
  • Indirect transmission: The virus can survive briefly on shared equipment (buckets, grooming kit, twitches, bit covers), hands of handlers, and potentially clothing. Fomite transmission, while less efficient than direct contact, contributes to spread in busy yards.
  • Oral-faecal route: ERV-B in particular can be shed in faeces and urine, broadening the potential routes of environmental contamination.
  • Group settings: Competitions, sales, racing yards, livery stables, and any situation where horses from multiple sources mix are high-risk environments for ERV transmission.

Symptoms and Signs

Clinical signs of ERV infection typically develop 3–7 days after exposure (incubation period) and include:

  • Fever (temperature above 38.5°C / 101.3°F), often the first sign
  • Bilateral nasal discharge, initially clear and watery, progressing to mucopurulent (thick, yellow-green) within a few days
  • Dry, hacking cough
  • Submandibular and parotid lymph node enlargement (swollen glands under the jaw and around the parotid region)
  • Reduced appetite and mild depression
  • Generalised stiffness and lethargy
  • Mild limb oedema (lower leg swelling) can occur, particularly with ERV-A
  • In young or immunocompromised horses, signs may be more severe and include more marked respiratory distress

Most uncomplicated ERV infections resolve within 2–3 weeks. However, secondary bacterial infections can complicate and prolong illness, particularly if the horse is returned to work too soon.

Diagnosis

Clinical signs of ERV overlap with several other equine respiratory diseases, making laboratory confirmation important:

  • Nasopharyngeal swabs: Virus isolation or PCR (polymerase chain reaction) testing of nasal swabs can identify ERV-A and ERV-B specifically.
  • Serology: Paired serum samples (acute and convalescent, taken 2–3 weeks apart) demonstrating a four-fold rise in neutralising antibody titres confirm recent ERV infection — useful retrospectively.
  • Paired bloods: Routine haematology may show a mild leucopaenia (reduced white cell count) or mild neutrophilia in acute disease.
  • Exclusion of other pathogens: Testing for equine influenza, equine herpesvirus 1 and 4, Streptococcus equi (strangles), and equine viral arteritis is important in an outbreak setting, as co-infections are possible and management differs.

Treatment

There is no specific antiviral treatment for ERV. Management is supportive:

  • Rest: This is the most important treatment. Horses should be removed from work immediately at the onset of illness. The “10-day rule” — one day of rest for every day of fever — is a practical guide. Returning to work too early significantly increases the risk of complications and chronic respiratory changes.
  • NSAIDs: Phenylbutazone or flunixin meglumine may be used to manage fever, pain, and malaise. They do not shorten the viral infection but improve welfare during the acute phase.
  • Antibiotics: Not indicated for uncomplicated viral ERV infection. They should be reserved for confirmed or strongly suspected secondary bacterial infections (e.g., bacterial pneumonia), as indicated by persistent or worsening fever, purulent nasal discharge, or abnormal lung sounds.
  • Nutritional support: Maintain appetite with palatable, easily consumed feed. Soaked hay or soft feeds may be preferred in horses with sore throats.
  • Isolation: Affected horses should be isolated from healthy horses immediately to prevent spread — minimum distance of 10 metres between isolation and main yard, with dedicated equipment.

Prevention

  • Biosecurity at competitions and sales: Avoid nose-to-nose contact with unknown horses. Do not share water buckets, feed utensils, or grooming equipment.
  • Quarantine new arrivals: Any horse returning from competition or entering a new yard should be kept isolated for 3 weeks before mixing with resident horses.
  • Hygiene: Regular handwashing, changing outer clothing before returning to the main yard, and disinfecting shared equipment reduces fomite transmission.
  • Vaccination: There is currently no commercially available vaccine specifically for ERV in the UK or most countries. Vaccination programmes against equine influenza and equine herpesvirus are important but will not protect against ERV.
  • Monitoring: Take temperatures daily on horses following return from competition or mixing events — catching the fever early enables prompt isolation before wider spread occurs.

Prognosis

Prognosis is generally good for uncomplicated ERV infection in otherwise healthy adult horses. Full recovery within 2–4 weeks is typical, and most horses return to their previous level of performance. Young foals and immunocompromised horses carry a more cautious prognosis. Secondary bacterial pneumonia is the most serious complication and warrants intensive veterinary management.

When to Call the Vet

Contact your vet if:

  • The horse has a temperature above 38.5°C for more than 24–48 hours
  • Nasal discharge becomes thick, yellow-green, and profuse
  • The horse is coughing deeply or showing laboured breathing
  • The horse is not eating or is very depressed
  • Multiple horses in a yard are affected — an outbreak requires coordinated management and likely testing
  • Signs are not improving or are worsening after 7–10 days

Frequently Asked Questions

Is Equine Rhinitis Virus the same as equine influenza?

No. Equine rhinitis virus (a Picornavirus) and equine influenza (an Orthomyxovirus) are entirely different viruses, though they can produce similar clinical signs. Influenza tends to produce more dramatic outbreaks with higher fever and more severe systemic illness, while ERV infections are often milder. Crucially, influenza vaccines do not protect against ERV. Specific PCR testing is needed to distinguish between the two.

Can ERV infect humans?

Equine Rhinitis Virus is not considered a significant zoonotic pathogen — there is no evidence of ERV causing disease in humans. However, standard hygiene precautions (handwashing, avoiding touching face after horse contact) are always sensible when handling sick animals.

How long should a horse be isolated after an ERV infection?

Isolation should be maintained for at least 3 weeks from the onset of signs, or until clinical signs have fully resolved and nasal shedding has stopped. As nasal shedding can persist for several weeks in some horses after clinical recovery, erring on the side of a longer isolation period is advisable in a yard where other horses are at high competition risk.

Should I vaccinate against ERV?

At present, there is no licensed ERV vaccine available in the UK or most other markets. The best protection is rigorous biosecurity — particularly around competition travel and new horse arrivals. Ensure your equine influenza and equine herpesvirus vaccination programmes are current, as these will protect against other common respiratory pathogens even though they do not cover ERV specifically.