Equine Rhinitis Virus

Equine Rhinitis Virus

Equine rhinitis viruses produce clinical signs similar to other viral respiratory infections, including serous or purulent nasal discharge.

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Respiratory viral infections are present in horses worldwide, with two of the most recognized viruses being equine influenza virus and equine herpesviruses. Although identified in the past mid-century, equine rhinitis viruses (ERVs) have emerged as significant contributors to equine respiratory infections. In the last decade, particularly, researchers have demonstrated that ERVs are highly prevalent in the horse population and are associated with clinical disease that can’t be differentiated from that caused by other viral respiratory infections. 

Until recently, researchers’ and veterinarians’ lack of knowledge about ERVs was largely due to their belief that these viruses were insignificant contributors to respiratory viral outbreaks and clinical disease. It is clear now that ERVs have circulated for decades within the global horse population. 

From a recent systematic respiratory outbreak study in Canada, along with an experimental infection study, we have established that the disease is characterized by increased body temperature, serous (clear, runny) to purulent (pus-containing) nasal discharges, submandibular lymphadenopathy (lymph node enlargement beneath the lower jaw), abnormal lung sounds, and excess airway secretions. In the challenge model, we detected mucus secretions up to 21 days post-infection. 

Because ERV clinical signs are nonspecific, veterinarians base disease diagnosis on common laboratory techniques such as virus isolation, serology (blood tests), and reverse transcription polymerase chain reaction (RT-PCR, a type of DNA test) on nasal and/or nasopharyngeal swabs. Veterinarians can detect viral DNA in nasal secretions, blood, and urine, but they usually isolate ERV from upper airway secretions collected using nasal and/or nasopharyngeal swabs from horses with suspected clinical respiratory viral infection. These secretions are thought to be the major source of infection spread. Isolation can be challenging when samples are collected past the acute phase of the disease, as is the case with most respiratory viruses, and this phase does not usually last more than three to four days. By the time horse owners call their veterinarians to examine such cases, most respiratory infections are beyond the acute phase. 

Veterinarians can use serology, on the other hand, as a confirmatory tool, or even as a primary diagnostic method. To establish a definitive diagnosis using this method, the veterinarian should analyze two serum samples collected 10 to 14 days apart. Conventionally, clinicians consider a fourfold increase in antibody titers (the concentration of specific antibodies in the blood produced to fight the disease agent, ERV) to be significant; however, titer changes are time-dependent and in some cases less-than-fourfold titer increases are significant. Molecular techniques such as conventional RT-PCR and real-time RT-PCR have become more routine practice in diagnostic veterinary laboratories due to their high sensitivity and quick turnaround times. Nevertheless, practitioners must interpret any positive results with caution because the test does not differentiate between the presence of live and/or remnant viral particles. 

Prevention and control measures for ERV are similar to those used to safeguard against other respiratory viruses (e.g., isolating newly acquired animals and applying routine disinfection methods). Currently a commercial ERV vaccine is only available in the United States, but approval is under way in other countries. The infection course and clinical duration of ERV infection are no different than those for other common respiratory viruses. For these reasons, provide ERV-infected animals basic medical care, adequate rest (if they’re athletes), and minimal environmental dust exposure, since dust, mold, and other pollutants increase airway irritation and inflammation.

About the Author

Andrés Diaz-Méndez

Andrés Diaz-Méndez, MedVet, MSc, PhD, is a postdoctoral fellow at the Firestone Equine Respiratory Research Laboratory.

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