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About Equine Flu 

Over the last two years there have been 52 recorded outbreaks of equine flu in the UK.

All isolated viruses are known to be of the Florida Clade 2 sublineage of H3N8 equine influenza and nearly all outbreaks were in unvaccinated horses or in those whose vaccinations were not up to date.3 The aim of Equine Flu Awareness Month is to boost awareness and vaccination compliance against this highly contagious disease.

Equine flu is not spread by direct contact alone. It can travel more than 2 kilometres in the air and be passed on via tack or equipment, quickly spreading from an individual to the whole yard and beyond.4, 5 Clinical signs can be subtle, especially in horses with a history of vaccination, and horses presenting with as little as a low-grade cough and/or serous nasal discharge should also arouse suspicion.

Historical precedent indicates a large outbreak occurs every 10 to 15 years.6 With the last major UK outbreak occurring in 2003, vaccination, surveillance of virus activity and development of vaccines to match the circulating strains are key to preventing an outbreak.

Equine Flu Awareness Month will integrate the Horserace Betting Levy Board (HBLB) Equine Influenza Surveillance Programme at the AHT with disease outbreak alerts and education to increase awareness of flu surveillance and vaccination, focusing on April 2016 and the start of the show season.

Surveillance in the UK

The HBLB Equine Influenza Surveillance Programme at the AHT monitors genetic and antigenic changes in equine flu viruses circulating in the UK. This scheme is sponsored by the HBLB and provides free advice and diagnostic testing for equine flu to all registered veterinary practices.

Samples from practicing vets are vitally important to find out where and how frequently outbreaks of flu are occurring, and are also used to monitor any changes that occur in currently circulating viruses.6

Sampling suspected cases of flu

Testing should be considered in unvaccinated and vaccinated horses showing clinical signs, and in any horses known to have come into contact with the virus as they can shed high levels of virus before showing any signs.

Appropriately timed sampling can provide important diagnostic information at yard level, but also makes a significant contribution to national equine flu surveillance.

The approach to diagnostic testing should be guided by the time that has elapsed since clinical signs were first noted. Nasopharyngeal (NP) swabbing is most likely to detect the virus in the days soon after clinical signs appear, when shedding is at its highest, whereas paired serology to detect a rising antibody titre can be used later in the course of disease.

Suggested approaches are:

  • 2–3 days from onset of clinical signs: NP swabs
  • 3–7 days from onset of clinical signs: NP swabs + 1st blood sample for serology, followed by a 2nd sample 14 days later


Best time to sample for Equine Flu

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1. Baker D. Equine Vet J 1986;18(2):93–96. 2. Merial Proactive Insight benchmarking 2015. 3. Equiflunet. Available at:
http://equiflunet.org.uk/ (Accessed December 2015). 4. Davis J et al. Transbound Emerg Dis 2009;56(1-2):31–38. 5. Firestone S et al. PLoS ONE 2012;7(4):e35284. 6. Elton D, Cullinane A. Equine Vet J 2013;45(6):768–769. 7. OIE Expert Surveillance Panel on Equine Influenza Vaccine Composition – conclusions and recommendations (March 2015). Available at: http://www.oie.int/our-scientific-expertise/specific-information-and-recommendations/equine-influenza/ (Accessed December 2015). 8. Paillot R et al. Vet Immunol Immunopathol 2006;112:225–233. 9. Paillot R et al. Vaccine 2007;25;5606–5612. 10. Paillot R et al. J Comp Path 2014;137;876–880. 11. Minke et al. Am J Vet Res 2007;68:213–219. 12. Paillot R et al. BEVA Congress. 2014. 13. Animal Health Trust, Merial sponsored Tell-Tail alerts 2014 and 2015. 14. Merial practice data, 2011. 15. Merial practice data, 2010–2013 inclusive.