Genetic characterization of equine arteritis virus during persistent infection of stallions.

The research article presents a study of how the genetic structure of the Equine Arteritis Virus (EAV) evolves during a persistent infection in male horses. The researchers analyzed the genetic sequence of the virus extracted from a carrier at two different times and found significant variations compared to the published genetic structure of EAV. They noted this variation notably in certain genes and proteins. Despite these differences, they suggest that these variations do not contribute to immune evasion, thus pointing to other determining factors for the virus’s persistence.

Research Method and Virus Genetic Characterization

• For their investigation, the research team focused on a specific carrier of the Equine Arteritis Virus, referred to as ‘CW’. They collected samples from this stallion at two separate occasions five years apart (CW96 and CW01).
• The researchers obtained the complete genome sequences of these viruses and compared them to the published sequence of EAV (known as EAV030).
• They discovered that the CW viruses only had between 85.6% and 85.7% nucleotide identity with the EAV030. There were unique insertions and a deletion in the leader sequence of the CW viruses, and their total nucleotide count exceeded that of the EAV030.
• Significant variations were found between the viruses present in the semen of stallion CW and the EAV030, particularly in the replicase gene (ORF1a and 1b). The most pronounced variation was observed in the segment of ORF1a encoding the nsp2 protein.
• The GP3 and GP5 envelope proteins (encoded by ORFs 3 and 5) also had significant variation when compared to the ORFs encoding the standard EAV proteins.

Variations and Persistence of Infection

• The team made comparative sequence analyses of the CW96 and CW01 viruses. They identified that ORFs 1a, 1b, and 7 remained highly conserved during a persistent infection, but there was considerable variation in ORFs 3 and 5.
• Despite these significant genetic changes, they found that the emergence of phenotypic viral variants did not allow the virus to evade a high-titre polyclonal equine antisera in neutralization assays. Therefore, they suggested that immune evasion may not be the mechanism permitting persistent EAV infection in male horses.
• They performed northern blot analyses on the RNA obtained from the viruses in ten different persistently infected stallions. All the viruses lacked large genomic deletions, suggesting that defective interfering particles are unlikely to play a substantial role in the maintenance or clearance of persistent EAV infection.