Multifocal Equine Influenza Outbreak with Vaccination Breakdown in Thoroughbred Racehorses.

Sarah Gildea,Marie Garvey,Rachel Lyons,Jacinta Gahan,Ann Cullinane,Pamela Lyons,Cathal Walsh

doi:10.3390/pathogens7020043

Sarah Gildea, Marie Garvey + Show 5 more

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https://doi.org/10.3390/pathogens7020043

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Abstract

Equine influenza (EI) outbreaks occurred on 19 premises in Ireland during 2014. Disease affected thoroughbred (TB) and non-TB horses/ponies on a variety of premises including four racing yards. Initial clinical signs presented on 16 premises within a two-month period. Extensive field investigations were undertaken, and the diagnostic effectiveness of a TaqMan RT-PCR assay was demonstrated in regularly-vaccinated and sub-clinically-affected horses. Epidemiological data and repeat clinical samples were collected from 305 horses, of which 40% were reported as clinically affected, 39% were identified as confirmed cases and 11% were sub-clinically affected. Multivariable analysis demonstrated a significant association between clinical signs and age, vaccination status and number of vaccine doses received. Vaccine breakdown was identified in 31% of horses with up to date vaccination records. This included 27 horses in four different racing yards. Genetic and antigenic analysis identified causal viruses as belonging to Clade 2 of the Florida sublineage (FCL2). At the time of this study, no commercially available EI vaccine in Ireland had been updated in line with World Organisation for Animal Health (OIE) recommendations to include a FCL2 virus. The findings of this study highlight the potential ease with which EI can spread among partially immune equine populations.

Highlights

Despite a comprehensive government-funded surveillance programme, mandatory vaccination of mobile equine populations and annual World Organisation for Animal Health (OIE) recommendations regarding vaccine composition, equine influenza (EI) remains one of the principal respiratory diseases affecting horses in Ireland, as it is in many countries around the world
Equine influenza was identified among horses and ponies on a total of 12 non-TB and seven TB premises in Ireland
This followed an absence of any confirmed EI activity in Ireland in 2013

Summary

Introduction

Despite a comprehensive government-funded surveillance programme, mandatory vaccination of mobile equine populations and annual World Organisation for Animal Health (OIE) recommendations regarding vaccine composition, equine influenza (EI) remains one of the principal respiratory diseases affecting horses in Ireland, as it is in many countries around the world. Virus strains circulating in Europe during the past decade have primarily been identified as Clade 2 of the Florida sublineage of the American lineage (FCL2) [1,2,3,4,5,6,7,8]. The failure of companies to update vaccines with epidemiologically-relevant virus strains facilitates disease spread even among well-vaccinated populations [9,10,11,12,13]. This, in conjunction with other host and environmental risk factors, results in a potential threat to equine industries in countries where participation in equestrian events is of fundamental economic importance.

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