Comparative analysis of ORF5 nucleotide sequences and amino acid sequences of the GP5 protein of equine arteritis virus (EAV) detected in the semen of stallions from Eastern Poland

The purpose of this study was to conduct a comparative analysis of the ORF5 gene fragment nucleotide sequences and the GP5 protein amino acid sequences formed on this matrix, for the equine arteritis virus (EAV) strains isolated from the semen of infected stallions from Eastern Poland. The study covered 41 stallions whose blood serum tested positive for antigens specific to the EAV. The presence of EAV genetic material was shown in material from 5 horses, in one of which permanent presence of viral RNA was detected over the entire 4-year study period (the material was sampled four times at yearly intervals). The mutual similarity among the ORF5 nucleotide sequences of EAV obtained in our own studies was 90.7-99%, whereas their similarity to a sequence of an isolate of the PL1 virus, determined in Polish horses previously, was 76.6-83%. A comparison of the primary structure of capsid glycoprotein encoded by the analysed section of ORF5 showed that amino acid substitution happens most frequently in region V1 of GP5, between positions 61 and 121. A phylogenetic analysis of our own isolates with sequences of viruses isolated from horses from the USA, Europe and New Zealand (available in the gene bank), made it possible to determine that the majority of the detected strains of the pathogen can be classified into the European group, with the Austrian strain of EAV as its protoplast.