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Breeder demographic survey and molecular period prevalence of equid alphaherpesvirus 1 in Ontario

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Title: Breeder demographic survey and molecular period prevalence of equid alphaherpesvirus 1 in Ontario
Author: Cooper, Carina
Department: Department of Pathobiology
Program: Pathobiology
Advisor: Lillie, Brandon
Abstract: Equid alphaherpesvirus 1 (EHV-1) causes disease in all ages of horses, from abortion and neonatal death to encephalomyelopathy in adults. The main objective of this thesis was to investigate the current opinions of breeders in Ontario, provide prevalence estimates, and describe current vaccine use for EHV-1, which have not been studied. A survey of 88 breeders in Ontario indicated 72.7 % currently vaccinate their herds, and most consult veterinarians for assistance only when encountering abortions, not respiratory disease. Most herds were vaccinated either twice annually or using a "pre-foaling protocol". In a follow up study, a period prevalence estimate was generated by sampling 381 broodmares from 42 farms across Ontario every two months from December 2016 through October 2017. Samples were collected from the nose, blood and vaginal mucosa and analysed using droplet digital PCR (ddPCR). A total of 85.0 % of broodmares were positive for EHV-1 at some point during the sampling period, and vagina was identified as a source of EHV-1, with viral DNA collected more often from the vagina than the nose. Using mixed logistic regression models, we found no association between virus presence and age or breed. Nasal shedding occurred more often in pregnant mares, and vaccination was only associated with reduced virus in blood samples. When describing the virus neutralization titer response in this population, 32.3 % of mares did not respond to vaccination, and 48.5 % of all mares had no biologically significant changes in titers over the sampling period. Using IgG subisotyping, differing immune responses were observed depending on vaccine product most recently administered. There was no association between IgG subisotype and neutralizing virus titers, nor was there an association with serological titers and ddPCR positivity. Titers did generally increase with age and were typically highest in Standardbred and Thoroughbreds. In conclusion, although most respondents were concerned about EHV-1 enough to vaccinate, many did not, leaving the population at risk for outbreaks. Although vaccines were widely used, they were not consistent in their immune stimulation, potentially creating a false sense of security among breeders. Furthermore, most broodmares harbour the virus and shed intermittently.
Date: 2020
Terms of Use: All items in the Atrium are protected by copyright with all rights reserved unless otherwise indicated.
Embargoed Until: 2021-08-19

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