Abstract
BackgroundEquine herpesvirus type 1 (EHV-1) infection is a major cause of pyrexias in winter among Japanese racehorses. In 2014–2015, the Japan Racing Association (JRA) changed the EHV-1 vaccine from an inactivated vaccine to a live vaccine (both produced by Nisseiken). To evaluate the effect of changing the vaccines, the capacities of these vaccines to induce virus-neutralizing (VN) antibodies were compared, and an epizootiological investigation of EHV-1 was performed at the JRA Ritto Training Center during epizootic periods from 2010–2011 to 2016–2017.ResultsThree-year-old horses that received the first dose of live vaccine showed higher geometric mean (GM) VN titers (205 and 220) than those that received inactivated vaccine (83, P < 0.05). The response rates after vaccination with the live vaccine (76 and 90%) were higher than that after vaccination with inactivated vaccine (42%, P < 0.05). Four-year-old horses from 2015 to 2017 that had received the live vaccine in the previous epizootic periods had higher GM titers (205 to 246) than those from 2011 to 2014, which had received the inactivated vaccine (139 to 164, P < 0.05). The estimated numbers of horses infected with EHV-1 or EHV-4, or both, in 2011–2012 (29 [95%CI: 21–37]) and 2013–2014 (37 [95%CI: 27–47]) were higher than those in the other periods (7 [95%CI: 2–12] to 16 [95%CI: 9–23]). Likewise, the seroconversion rates to EHV-1 in horses that stayed at the training center in 2011–2012 (66.0%) and 2013–2014 (52.0%) were higher than those in the other periods (12.0 to 28.6%).ConclusionsThe live EHV-1 vaccine is highly immunogenic and provides greater VN antibody responses than the inactivated vaccine. Unlike the period when the policy was to use inactivated vaccine, there was no detectable epizootic EHV-1 infection at the training center during three consecutive periods after the introduction of the live vaccine. These results suggest that the replacement of inactivated vaccine with live vaccine, together with the achievement of high vaccination coverage, reinforced the herd effect, and contributed to better control of EHV-1 epizootics in the training center.
Highlights
Equine herpesvirus type 1 (EHV-1) infection is a major cause of pyrexias in winter among Japanese racehorses
Pyrexia caused by EHV-1 epizootics among Japanese racehorses has been an important issue, because it delays training schedules and cause horses to be withdrawn from races [2]
Administrative coverage of EHV-1 vaccine in the 3-yearold population and in the whole population We investigated the coverages of the EHV-1 vaccine in the 3-year-old population and in the whole population of all ages at the training center on 1 January of each epizootic period from 2010–2011 to 2016–2017
Summary
Equine herpesvirus type 1 (EHV-1) infection is a major cause of pyrexias in winter among Japanese racehorses. To evaluate the effect of changing the vaccines, the capacities of these vaccines to induce virus-neutralizing (VN) antibodies were compared, and an epizootiological investigation of EHV-1 was performed at the JRA Ritto Training Center during epizootic periods from 2010–2011 to 2016–2017. Pyrexia caused by EHV-1 epizootics among Japanese racehorses has been an important issue, because it delays training schedules and cause horses to be withdrawn from races [2]. The horses are usually introduced into the training centers at two-year-old, and most of them received first contact with EHV-1 during their first winter there [3]. EHV-4 infection in the training centers is generally sporadic and most cases are subclinical [3]
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