Equine influenza – surveillance and control

Equine influenza virus (EIV) is considered the most important respiratory virus of horses because it is highly contagious and has the potential to disrupt major equestrian events. Equine influenza (EI) can be controlled by vaccination but it has been demonstrated repeatedly in the field that antigenic drift impacts on vaccine efficacy. EI surveillance maintains awareness of emergence and international spread of antigenic variants. It not only serves as an early warning system for horse owners, trainers and veterinary clinicians but is fundamental to influenza control programmes based on vaccination. Data on outbreaks of EI and strain characterisation is reviewed annually by an Expert Surveillance Panel (ESP) including representatives from OIE and WHO. This panel makes recommendations on the need to update vaccines based on analysis of evidence of disease in well vaccinated horses, antigenic changes, genetic changes and when possible, experimental challenge data. However, the disparity in the level of surveillance and virus collection in different countries results in potentially biased information about the relative prevalence of different viruses. There is a need for increased surveillance on a global level and a greater awareness of the benefits of updating the vaccines. The vaccine companies have traditionally been slow to respond to the ESP recommendations. Veterinary clinicians have a major role to play in purchasing vaccines with epidemiologically relevant strains and promoting their benefits to their clients.