Report of the International Equine Influenza Roundtable Expert Meeting at Le Touquet, Normandy, February 2013.

Abstract

Equine influenza (EI) is an important equine respiratory pathogen and a high-priority disease for the equine industry globally. Equine influenza virus (EIV) has a global distribution; it is endemic in many countries and there are occasional incursions in Japan, South Africa and Hong Kong, with only Australia, New Zealand and Iceland being considered free. In 2007, EIV was introduced into Japan and Australia, severely disrupting the equine industry, with control and eradication costing an estimated $AU1.6 billion in Australia. Equine influenza virus has subsequently been detected in recently imported, vaccinated horses in quarantine stations in Japan and Dubai. Many of the bodies responsible for regulating racing and equestrian sport in Europe and North America have required EIV vaccination since the 1980s, in order to safeguard competition and facilitate the movement of horses. The majority of horses in the racing and competition sectors are vaccinated against EIV, but outside these sectors the proportion of vaccinated horses is unknown. In most countries, too few horses are vaccinated to provide the herd protection required to prevent propagation of an epizootic, if an incursion of an EIV strain with sufficient antigenic differences to currently circulating strains were to occur. Surveillance in order to monitor outbreaks and to characterise the antigenic and genetic characteristics of circulating EIV strains, in particular changes in the haemagglutinin (HA) surface glycoprotein, is central to EI control. France, Germany, Ireland, the UK and the USA have the most extensive surveillance schemes. Haemagglutination inhibition (HI) assays and HA sequence data allow predictions of antigenic and genetic drift to be made. Antigenic mapping (cartography) is used to assist interpretation of HI data. Haemagglutinin sequence data are shared between collaborating laboratories, which facilitates phylogenetic analysis and mapping of the evolutionary changes in EIV. The expert surveillance panel (ESP) of the World Organisation for Animal Health (OIE) reviews these data and publishes recommendations for EI vaccine strain updates periodically. Most recently (2010), the ESP recommended that H7N7 viruses and Eurasian H3N8 viruses are no longer required and that strains representative of clade 1 (A/eq/South Africa/04/ 2003-like or A/eq/Ohio/2003-like viruses) and clade 2 (A/eq/Richmond/1/ 2007-like viruses) viruses of the Florida sublineage should be included. Equine H3N8 viruses change more slowly than human influenza viruses, and thus ESP recommendations have changed only twice in the last 8 years. However, at the time of writing, there are no EIV vaccines meeting the European regulatory requirements that are completely compliant with these recommendations, probably because updating EI vaccines is comparatively burdensome, time consuming and expensive. Vaccination against EIV is a highly important control measure. Vaccination has had a significant beneficial effect on the prevalence of EIV infection, but there is no room for complacency: outbreaks still occur annually, despite vaccination. In 2012, individual cases or outbreaks of EI associated with clade 1 and clade 2 viruses, closely related antigenically, but not identical, to the recommended vaccine strains were recorded in both nonvaccinated and vaccinated horses in Argentina, Chile, France, Germany, Ireland, the UK and the USA. The lack of clarity and the conflicting opinions on key aspects of EI within the European equine industry create a risk that the value of EI vaccination may be challenged, with the potential outcome that vaccination, and hence (national) herd protection, may fall to a level at which the prevalence of EI increases, equine welfare decreases and the equine industry experiences significant economic losses through interference with competition, breeding, movement and trade. A meeting of international experts on EI was held in Le Touquet, France, on 6 February 2013. The goal of the meeting was to address and reach consensus on some of the most pressing questions on EI and its control, including surveillance, the spectrum of clinical disease, diagnosis, biosecurity, protective immunity, key factors in vaccine selection, vaccine efficacy, vaccine strain updates, reasons for vaccination failure and future research. Nine critical questions on current issues in EIV became apparent during the panel’s discussions and form the basis for this report.