E5 nucleotide polymorphisms suggest quasispecies occurrence in BPV-1 sub-clinically infected horses.

BPV-1 is known as the main causative agent of equine sarcoid, but the virus has also been detected in skin and blood of healthy horses. Previous reports demonstrated the presence of E5 variants in sarcoids of donkeys and horses; we investigated whether this genetic variability might be also found in BPV-1, PBMC associated, of sub-clinically infected horses. With this aim, we analyzed the E5 gene of 21 BPV-1 strains from diseased and sub-clinically infected horses. Our analyses lead us to demonstrate that multiple sequence variants can be present in the blood of sub-clinically infected horses, with alternative bases corresponding to either synonymous or non-synonymous codons in the E5 oncogene sequences. The results give support to the proposed existence of "equine adapted" BPV-1 strains with the occurrence of viral variants, resembling quasispecies, in clinically healthy horses with viremia.