Equine rhinovirus 1 is more closely related to foot-and-mouth disease virus than to other picornaviruses.

Equine rhinovirus 1 (ERhV1) is a respiratory pathogen of horses which has an uncertain taxonomic status. We have determined the nucleotide sequence of the ERhV1 genome except for a small region at the 5' end. The predicted polyprotein was encoded by 6741 nucleotides and possessed a typical picornavirus proteolytic cleavage pattern, including a leader polypeptide. The genomic structure and predicted amino acid sequence of ERhV1 were more similar to those of foot-and-mouth disease viruses (FMDVs), the only members of the aphthovirus genus, than to those of other picornaviruses. Features which were most similar to FMDV included a 16-amino acid 2A protein which was 87.5% identical in sequence of FMDV 2A, a leader (L) protein similar in size to FMDV Lab and the possibility of a truncated L protein similar in size to FMDV Lb, and a 3C protease which recognizes different cleavage sites. However, unlike FMDV, ERhV1 had only one copy of the 3B (VPg) polypeptide. The phylogenetic relationships of the ERhV1 sequence and nucleotide sequences of representative species of the five genera of the family Picornaviridae were examined. Nucleotide sequences coding for the complete polyprotein, the RNA polymerase, and VP1 were analyzed separately. The phylogenetic trees confirmed that ERhV1 was more closely related to FMDV than to other picornaviruses and suggested that ERhV1 may be a member, albeit very distant, of the aphthovirus genus.