Genetic variation and phylogenetic analysis of 22 French isolates of equine arteritis virus.

The researchers investigated the genetic diversity and evolutionary relationships among multiple strains of the equine arteritis virus (EAV) in France, finding significant variation and suggesting different geographic origins of these strains.

Methodology and Genetic Diversity

• The researchers collected 22 isolates of EAV from French horses across four breeding seasons, spanning from 2001 to 2004.
• They studied the genetic variation of these EAV strains by sequencing certain regions of the virus’s genome, known as open reading frames (ORFs) 2a-7.
• The nucleotide sequences of these isolates were compared to the prototypical Bucyrus strain of EAV and to each other.
• They found considerable genetic diversity among the French EAV strains, with the ORFs varying by between 14 and 328 nucleotides compared to the Bucyrus strain and up to 346 differences between the strains with each other.

Phylogenetic Analysis and Geographic Clustering

• Phylogenetic analysis, which is used to infer the evolutionary relationships between different strains, was carried out based on partial ORF5 sequences of the 22 French isolates, combined with data from an additional 216 EAV strains sourced from GenBank, a global genetics database.
• This analysis revealed that the global EAV strains clustered into two major groups: North American and European. Furthermore, the European strains were divided into two large subgroups – EU-1 and EU-2.
• A similar pattern of grouping was observed when phylogenetic analysis was performed using 100 EAV ORF3 sequences.

Temporal Grouping and Geographic Origins

• Interestingly, the researchers found that the EAV isolates obtained in France before January 28, 2003, clustered with either the EU-1 or EU-2 subgroup, indicating these were locally circulating strains.
• However, the 11 EAV isolates obtained after January 30, 2003, clustered with the North American group, strongly suggesting that these strains were introduced into France around that time, possibly due to international movement of horses.