The influenza virus (EIV)
Equine influenza is a major cause of respiratory disease in horse populations around the world. Current viruses belong to the subtype H3N8 and, like human influenza viruses, undergo antigenic drift due to the gradual accumulation of mutations in the surface glycoproteins. In particular, changes in the viral haemagglutinin (HA) help the virus avoid immunity acquired from previous infection or vaccination. As a result, vaccine strains need to be updated regularly. Current OIE recommendations are to include a representative strain from each of the two sublineages of EIV, Florida Clade 1 and Florida Clade 2.
|Cartoon showing influenza virus structure
Image kindly supplied by Dr Paul Digard
|Structure of influenza HA showing amino acid
differences between Florida clade 1 and
Florida clade 2 viruses