Complete genomic characterization of bovine papillomavirus type 1 and 2 strains infers ongoing cross-species transmission between cattle and horses.

This research demonstrates that bovine papillomavirus (BPV) types 1 and 2, which are the cause of the most common skin tumor in horses called equine sarcoid, seem to be constantly transmitted between cattle and horses. Despite the identification of potential horse-specific mutations in the genome of the viruses, these do not fully explain the different responses to infection in horse and cattle populations.

Research Methodology

• A total of 98 complete BPV-1 and BPV-2 genomes were identified and examined. Extraction of these genomes was facilitated by adopting the Nanopore sequencing approach, a technology that allows long read sequencing of individual molecules in real-time.
• The researchers utilized separate BPV-1 and BPV-2 alignments in developing Bayesian phylogenetic trees. Phylogenetic tree construction allows the tracing of the evolution and divergence of different virus strains.
• The possible association of phylogeny with host species was explored using Bayesian Tip-association Significance software (BaTS), a program that allows for a statistical evaluation of trait associations with phylogenies.

Key Findings

• A total of 179 unique BPV-1 and 128 BPV-2 replacements were discovered. Among these substitutions, the E2 coding region in the viral genome contained an unusually high rate of non-synonymous mutations (changes that result in producing different amino acids), representing 81 % of all mutations found in the region.
• Notably, sizable deletions in the L1/L2 region of up to 1.5 kb were found only in samples derived from horses. The L1 and L2 proteins are important constituents of viral capsids (the outer casing of viral particles).
• However, the most commonly detected single nucleotide polymorphisms, changes in a single nucleotide at specific locations in genomes, were common between equine and bovine hosts. This observation coincided with BaTS analysis, signifying no significant phylogeny-host relationship.
• The study identified potential horse-specific mutations, but these didn’t result in the creation of horse-adapted genetic variants of BPV.

Conclusion

• The outcome of this study provides significant insights into the cross-species transmission of BPV from cattle to horses. It suggests that this transmission is an ongoing process instead of being an ancient event followed by the circulation of horse-adapted BPV strains in horse populations.