Bit & Bridle

Equine Rhinitis Virus Infections

Other Names

  • Equine rhinitis A virus (ERAV)
  • Equine rhinitis B virus (ERBV)
  • Equine picornavirus infections
  • Equine rhinovirus

What are Equine Rhinitis Virus Infections?

Equine rhinitis viruses (ERVs) are RNA viruses belonging to the Picornaviridae family that cause upper respiratory tract disease in horses. Two distinct species have been identified: Equine Rhinitis A Virus (ERAV) and Equine Rhinitis B Virus (ERBV), each comprising multiple serotypes. These viruses are distinct from equine influenza and equine herpesviruses, though they produce clinically similar signs of upper respiratory disease.

Equine rhinitis virus infections are widely distributed in horse populations worldwide and are considered endemic in many regions. The disease is most commonly seen as a sporadic illness in individual horses or as outbreaks in yards with multiple horses, particularly in young animals or those exposed to new horses through competition or sales. While generally self-limiting, ERV infections can cause significant economic impact through lost training and competition time.

Causes

ERAV and ERBV are transmitted primarily through direct contact with infected horses and through respiratory droplets. The viruses can survive on surfaces, equipment, and clothing, making indirect transmission possible in shared facilities. Key risk factors include:

  • Introduction of new horses onto a yard without appropriate quarantine periods
  • Attendance at competitions, shows, or race meets where horses from multiple sources mix
  • Transport — the stress of travelling combined with exposure to other horses significantly increases infection risk
  • Overcrowding or poor ventilation in stabling
  • Young horses and those without prior exposure or immunity

Seroprevalence studies in various countries suggest that a high proportion of horses have been exposed to ERVs at some point, indicating widespread circulation in equine populations.

Symptoms and Signs

Clinical signs are typically those of an upper respiratory tract infection:

  • Serous (watery) nasal discharge, which may become mucopurulent (yellow-green) if secondary bacterial infection develops
  • Fever (38.5–40.5°C)
  • Pharyngitis — reddened, inflamed throat visible on endoscopy
  • Mandibular lymph node enlargement
  • Coughing — typically mild to moderate
  • Lethargy and reduced appetite
  • Reduced performance or exercise intolerance
  • Occasional mild limb oedema or stiffness

Symptoms usually resolve within one to two weeks, though post-viral fatigue and performance depression can persist for several additional weeks. Viruria (viral shedding in urine) can occur with ERAV, which is unusual for respiratory pathogens and may contribute to transmission.

Diagnosis

  • Clinical assessment: ERV infection cannot be reliably distinguished from other equine respiratory viral diseases (influenza, EHV) on clinical signs alone.
  • PCR testing: Real-time RT-PCR on nasopharyngeal swabs is the most sensitive and specific diagnostic test for ERAV and ERBV. Urine PCR may also be positive in ERAV infections.
  • Virus isolation: Laboratory culture from nasopharyngeal swabs can confirm the diagnosis but is slower than PCR.
  • Serology: Demonstration of a four-fold rise in antibody titres between acute and convalescent samples (taken 2–3 weeks apart) provides retrospective confirmation.
  • Haematology: May show leucopenia (low white cell count) during the acute febrile phase.

Treatment

There is no specific antiviral treatment for equine rhinitis virus infections. Management is supportive:

  • Rest: Horses should be rested from training for the duration of the illness and for a period afterwards to allow full recovery. The general guideline is one day off for every day of fever, with additional time for return to full fitness.
  • NSAIDs: Phenylbutazone or flunixin meglumine to manage fever and discomfort.
  • Antibiotics: Not indicated for the primary viral infection but may be warranted if secondary bacterial infection is confirmed or strongly suspected.
  • Nutritional support: Ensure adequate feed and water intake, providing palatable feeds if appetite is reduced.
  • Good stable management: Excellent ventilation, avoidance of dusty bedding or hay, and minimising stress.
  • Isolation: Affected horses should be isolated from healthy horses to reduce spread on the yard.

Prevention

  • Implement and enforce a quarantine policy for all new horses arriving on the yard — a minimum of three weeks is recommended.
  • Maintain good biosecurity at competitions and events.
  • Ensure adequate stable ventilation to reduce airborne viral load.
  • Although vaccines for ERAV have been studied, no commercially licensed vaccine is currently widely available. Vaccination against equine influenza and EHV-1/4 remains important for overall respiratory disease control.
  • Regularly clean and disinfect shared equipment, tack, water buckets, and vehicles.

Prognosis

The prognosis for equine rhinitis virus infections is generally excellent. Most horses make a full recovery within two to three weeks with appropriate rest and supportive care. Secondary bacterial pneumonia is an uncommon but more serious complication that can extend recovery time. Horses returned to work too quickly following respiratory viral illness are at risk of more prolonged convalescence and potential cardiac complications (such as myocarditis), so adequate rest should never be shortened to meet competition schedules.

When to Call the Vet

Contact your vet if your horse:

  • Develops a fever exceeding 38.5°C
  • Has persistent or worsening nasal discharge
  • Is coughing persistently or having difficulty breathing
  • Is part of a yard where multiple horses are becoming ill in quick succession
  • Fails to improve after a week of rest and supportive care

Frequently Asked Questions

Is equine rhinitis virus the same as equine influenza?

No — they are distinct viruses. Equine influenza is caused by influenza A viruses (H3N8 and H7N7 subtypes), while equine rhinitis viruses belong to the Picornaviridae family. Both cause respiratory illness with overlapping clinical signs, which is why laboratory testing is needed to differentiate them.

Can ERV be prevented by vaccination?

Currently, no widely commercially available vaccine exists for equine rhinitis viruses in most countries. Vaccination for equine influenza and EHV remains important as part of a comprehensive respiratory disease control programme, but these vaccines do not protect against ERV.

Why can ERAV be found in urine?

ERAV is unusual among respiratory viruses in that it can establish a systemic infection and be shed in urine. This viruria means that infected horses can contaminate their environment beyond the respiratory droplets usually associated with respiratory viruses, which has implications for biosecurity and disinfection protocols.

How long should a horse rest after a rhinitis virus infection?

As a minimum, horses should be rested until clinical signs have fully resolved and they are eating normally and afebrile. A useful guideline is to allow at least one week of rest per week of clinical illness before very gradually returning to work. Most horses require two to four weeks total rest before resuming light work.