Equine influenza virus from the 1991 Swedish epizootic shows major genetic and antigenic divergence from the prototype virus.

The study reveals significant genetic and antigenic changes in the equine influenza virus from the 1991 Swedish epidemic compared to the prototype virus. It emphasizes that these disparities require frequent updates of the vaccine to control future outbreaks.

Overview of the Study

• The study focuses on understanding how the H3N8 equine influenza virus involved in the 1991 Swedish epidemic differs from A/eq 2/Fontainebleau/79, a prototype virus that represents the Swedish vaccine strain.
• This investigation was conducted using hemagglutination inhibition tests to observe the antigenic properties of the virus strains.
• The researchers also conducted a comparative analysis of the amino acid sequence of the hemagglutinin (HA) from an isolate from the 1991 outbreak and that of the A/eq 2/Fontainebleau/79 strain.

Findings of the Study

• The findings revealed 23 amino acid substitutions in the HA of the 1991 isolate when compared with the A/eq 2/Fontainebleau/79 strain.
• Among these, 10 substitutions were found in areas of the HA known to bond with antibodies in human H3 influenza viruses.
• The amino acid changes and the serological data gathered indicate that a substantial antigenic drift (evolutionary change) has occurred in the equine H3N8 viruses in Sweden.

Implications of the Findings

• These findings suggest that there have been significant evolutionary changes in the H3N8 equine influenza virus since the prototype strain used in vaccines.
• This indicates that the current vaccines may not be fully effective against recent strains of the virus due to these antigenic changes.
• Given the observed genetic and antigenic divergence, the study concludes that it is essential to regularly update the strains of the virus included in vaccines to control future equine influenza outbreaks effectively.