Sequence analysis of ORFs 5, 6 and 7 of equine arteritis virus during persistent infection of the stallion--a 7-year study.

Nucleotide and amino acid sequences of ORFs 5, 6 and 7 of EAV during persistent infection in the stallion of the Malopolska breed were analysed in the study. A total of 11 blood and semen samples were collected between 2004 and 2011. The titre of specific EAV antibodies in this carrier stallion was maintained at a high level throughout the study and was equal approximately 1:128. The sequence analysis of ORF5 showed 16 variable sites including 12 with synonymous substitutions and 4 with non-synonymous substitutions. The degree of nucleotide sequence identity among the strains ranged from 98.92% to 100%, whereas amino acid homology ranged from 98.06% to 100%. Ten substitutions were identified including 7 with synonymous mutations and 3 with non-synonymous mutations in ORF6. The degree of similarities among the strains ranged from 94.55 to 100% and from 98.41% to 100% at the level of nucleotide and amino acid sequence, respectively. Only a single point mutation at position 255 of ORF7 (99.6% identity) was found in nucleotide sequences of these strains. Phylogenetic analysis showed that all strains present in the semen of this carrier stallion created a separate cluster of "quasi-species" within the second European subgroup of EAV.