Characterization of an Equine Rhinitis A Virus (ERAV/ON/05) and Development of an Experimental Infection Model in Horses
In 2005 an equine rhinitis A virus (ERAV) isolate was recovered from a febrile horse during a respiratory outbreak in Ontario. This isolate (ERAV/ON/05) was propagated in cell culture and used to study its genomic characteristics and to investigate the clinical features in experimentally infected ponies. The fulllength genome of this isolate was sequenced and compared with other ERAV available in GenBank. The isolate genome is 7839 nucleotides (nts) in length with a variable 5’UTR and a more conserved 3’UTR. When the isolate was compared to other reported ERAV, an insertion of 13 nts in the 5’UTR was identified. Phylogenetic analysis demonstrated that ERAV/ON/05 was closely related to the ERAV/PERV isolate, which was recovered in 1962 in the United Kingdom. An experimental model was developed to study the clinical infection in naïve healthy ponies (ERAV/ON/05 n=4 and placebo n=4). ERAV/ON/05 induced clinical respiratory disease compared to placebo. The clinical signs consisted of pyrexia, nasal discharge, increased and abnormal lung sounds, increased size of submandibular lymph nodes and persistent mucopus in the trachea (up to 21 days post-infection). The virus was isolated from the lower and upper airways up to day 7 post-infection, corresponding with the detection of neutralizing ERAV antibodies. Assessment of the cytokine profile from bronchoalveolar lavage (BAL) cells demonstrated that this infection induced down-regulation of the mRNA expression of IL-4. One year later, four previously infected ponies with neutralizing antibodies to ERAV were assigned to a reinfection trial. None of the re-infected ponies developed clinical disease, and only one animal had a four-fold increase in antibody titres to ERAV. Attempts to recover the virus from the re-infected ponies using cell culture were negative; however, a down-regulation of the mRNA expression of IL-4 and IFN-β was identified in BAL cells. In conclusion, this study shows that the genome of ERAV has not significantly changed in the last 50 years and more importantly the virus induces clinical respiratory disease similar to other common equine respiratory viruses.