Multifocal Equine Influenza Outbreak with Vaccination Breakdown in Thoroughbred Racehorses

• Published in: Pathogens (Basel) Vol. 7; no. 2; p. 43
• Main Authors: Gildea, Sarah, Garvey, Marie, Lyons, Pamela, Lyons, Rachel, Gahan, Jacinta, Walsh, Cathal, Cullinane, Ann
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 17-04-2018; MDPI
• Subjects: Animal health; Antigens; Breakdown; Diagnostic systems; Disease; Epidemiology; equine influenza Clade 2; Field tests; Genetic analysis; Horses; Influenza; Outbreaks; Polymerase chain reaction; Racehorses; Racing; TaqMan RT-PCR; thoroughbred racehorses; Vaccination; vaccination breakdown; Vaccines; Viruses; Ireland; equine influenza Clade 2; vaccination breakdown; thoroughbred racehorses; TaqMan RT-PCR
• ISSN: 2076-0817; 2076-0817
• DOI: 10.3390/pathogens7020043

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.