NS-gene based phylogenetic analysis of equine influenza viruses isolated in Poland.

This research article describes a phylogenetic analysis of equine influenza viruses in Poland utilizing the NS (nonstructural) gene. The authors identified unique nucleotide and amino acid positions that may distinctively characterize certain strains of the virus, contributing to understanding of virus evolution and potentially identifying previously unrecognized evolutionary trends.

Background on Phylogenetic Analysis

• The study is based on phylogenetic analysis, a method widely used for understanding the evolutionary relationships among different species or strains of viruses. By comparing the genetic information, it can help in tracing the evolutionary history back to their most recent common ancestors.
• Commonly, this type of analysis with influenza viruses involves the study of hemagglutinin or neuraminidase genes – the two major proteins that determine the subtype of the virus. In this research, however, the focus was on the NS gene, which is more conservative (less likely to mutate).

Analysis of Equine Influenza Viruses

• The researchers studied the full length NS sequences for equine influenza viruses, including Polish strains, from the GenBank database. They were particularly interested in certain nucleotide and amino acid positions that might distinguish the Florida sublineage, and EIV strains of Florida 2 isolated after 2007.
• A group of equine influenza virus strains (“Aboyne-like”) distinguished by specific substitutions in the NS sequences was identified. These included A/eq/Pulawy/2005, A/eq/Aboyne/1/2005, and A/eq/Lincolnshire/1/2006. These substitutions led to changes in the NS1 protein and NEP – two proteins coded by the NS gene.

Hypotheses on the Origin of “Aboyne-like” Strain

• The researchers proposed two hypotheses regarding the origin of the “Aboyne-like” group: one possibility is independent transfers of avian influenza viruses into the equine population; the other possibility is reassortment between H7N7 and H3N8 strains of equine influenza virus.
• Similarities observed between the NS sequences of “Aboyne-like” viruses and those isolated in the 1950s or 1970s support a hypothesis of a “frozen evolution”, a phenomenon that explains why these viruses have conserved certain genetic characteristics over time.