Recent outbreaks of respiratory disease in horses have led to the discovery of the emerging importance of Equine Rhinitis Virus as a cause of respiratory illness. Equine Influenza Virus and Equine Herpes Virus are the most common causes of equine respiratory illness, but more recently, Equine Rhinitis Virus has been implicated. This virus was once thought to be of little clinical significance, but we now know that it can cause serious illness.

Equine Rhinitis Virus should not be confused with rhinopneumonitis, which is caused by Equine Herpes Virus. There are two forms of the Equine Rhinitis Virus (ERV), equine rhinitis A (ERAV) and equine rhinitis B (ERBV). Serologic studies show that ERV is distributed worldwide, with prevalence ranging from 20%-70% in countries including the United Kingdom, the United States, Canada, Australia, New Zealand, Germany, and Japan.

Horses have been documented to be infected with both influenza virus and ERV, suggesting that some outbreaks may be caused by both viruses.

Since the virus has not been well studied, we do not know much about how it is transmitted. It is likely, however, that it is transmitted similarly to other respiratory viruses through direct contact with nasal secretions and aerosolized secretions when horses cough or sneeze. Secretions on fomites such as stall doors, buckets, troughs, etc., may also be sources of transmission.

What are the Clinical Signs?

Clinically, horses present with typical signs of respiratory disease. These signs include:

• Fever
• Swollen painful submandibular lymph nodes
• Seromucoid discharge that progressively becomes more mucoid
• Ocular discharge
• Dry cough
• Occasionally lower leg swelling
• Increase in respiratory rate and bronchial sounds
• Anorexia

How Does TEVA Diagnose ERV?

Diagnosis is not easy, but relies on virus isolation, polymerase chain reaction (PCR) and serology. Most labs in the U.S. are not routinely testing for ERV and currently only two laboratories are set up to do so, so we veterinarians have to ask specifically for this virus to be included in testing. PCR is a relatively quick screening method, but it does not differentiate between dead virus that may be present after an infection is cleared, virus that is not causing clinical signs, or virus responsible for active infection. Paired serology, watching for a 4-fold increase in antibodies in blood samples taken at 10-24 days apart is confirmatory for the disease.

What is the Treatment?

Treatment is mostly symptomatic. Non-steroidal anti-inflammatories can decrease the fever and make the horse feel more comfortable. Antibiotics may be prescribed as well. The damage the virus causes to the upper and lower respiratory tract makes the horse more susceptible to secondary bacterial infections. Rest is critical and may be required for up to 21 days. Without rest, inflammation persists and makes the respiratory tract more sensitive to dust, mold, and other allergens and can result in lower airway inflammation or inflammatory airway disease. It takes the respiratory epithelium 21 days to repair after damage. Any exercise prior to this will cause prolonged inflammation that can affect a horse’s performance for the rest of its life. Rest can include turnout, which is preferred to get the horse out of the dusty, moldy environment of a stall.

How can Horse Owners Prevent this Illness?

Good hygiene practices are paramount to preventing ERV. Quarantine any new horses for 2 weeks to prevent introducing viruses to the rest of the barn. Make sure that any sick horses are also quarantined and that all buckets, shared cleaning utensils, etc., are disinfected. Handlers must wash hands after being with sick horses.

There is now a vaccine available from Boehringer Ingelheim to protect against ERAV. You should speak with your TEVA veterinarian to see if this vaccine is right for your horse and your situation.

Registered 2013 by Equestrian Collections
Author: Sallie S. Hyman, VMD, DACVIM, CVA

Information in this article is for educational purposes only and is not a substitute for evaluation by an equine professional. In particular, all horse owners should seek advice and treatment from a licensed veterinarian, such as TEVA, for their horses' medical care.

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