How to cite this article: Vet. Res. (2010) 41:19
DOI: 10.1051/vetres/2009067

Comparison of two modern vaccines and previous influenza infection against challenge with an equine influenza virus from the Australian 2007 outbreak

Neil A. Bryant¹, Romain Paillot¹, Adam S. Rash¹, Elizabeth Medcalf¹, Fernando Montesso¹, Julie Ross^{1, 2}, James Watson³, Martyn Jeggo³, Nicola S. Lewis^{1, 4}, J. Richard Newton¹ and Debra M. Elton<sup>1

1</sup>  Animal Health Trust, Centre for Preventive Medicine, Lanwades Park, Kentford, Newmarket, CB8 7UU, United Kingdom
²  Present address: Department for Environment. Food and Rural Affairs, Nobel House, 17 Smith Square, London, SW1P 3JR, United Kingdom
³  CSIRO Livestock Industries, Australian Animal Health Laboratory (AAHL), East Geelong VIC 3219, Australia
⁴  Department of Zoology, University of Cambridge, Downing Street, Cambridge, CB2 3EJ, United Kingdom

Received 23 July 2009; accepted 28 October 2009; published online 29 October 2009

Abstract - During 2007, large outbreaks of equine influenza (EI) caused by Florida sublineage Clade 1 viruses affected horse populations in Japan and Australia. The likely protection that would be provided by two modern vaccines commercially available in the European Union (an ISCOM-based and a canarypox-based vaccine) at the time of the outbreaks was determined. Vaccinated ponies were challenged with a representative outbreak isolate (A/eq/Sydney/2888-8/07) and levels of protection were compared.A group of ponies infected 18 months previously with a phylogenetically-related isolate from 2003 (A/eq/South Africa/4/03) was also challenged with the 2007 outbreak virus. After experimental infection with A/eq/Sydney/2888-8/07, unvaccinated control ponies all showed clinical signs of infection together with virus shedding. Protection achieved by both vaccination or long-term immunity induced by previous exposure to equine influenza virus (EIV) was characterised by minor signs of disease and reduced virus shedding when compared with unvaccinated control ponies. The three different methods of virus titration in embryonated hens' eggs, EIV NP-ELISA and quantitative RT-PCR were used to monitor EIV shedding and results were compared. Though the majority of previously infected ponies had low antibody levels at the time of challenge, they demonstrated good clinical protection and limited virus shedding. In summary, we demonstrate that vaccination with current EIV vaccines would partially protect against infection with A/eq/Sydney/2888-8/07-like strains and would help to limit the spread of disease in our vaccinated horse population.

Key words: equine influenza / vaccine / protection / outbreak / antibody

Corresponding author: romain.paillot@aht.org.uk

© INRA, EDP Sciences 2009