Epidemiological investigations of the New Zealand horse population and the control of equine influenza : a thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Veterinary Epidemiology, Massey University, Palmerston North, New Zealand

Abstract

The aim of this thesis was to develop a disease model to evaluate the effectiveness of movement restriction and vaccination for the control of equine influenza in the New Zealand horse population. In order to achieve this aim, a series of epidemiological investigations into the characteristics, movement behaviour and biosecurity practices of the New Zealand horse population were conducted. The New Zealand equine population has never experienced an outbreak of the highly infectious, respiratory virus, equine influenza (EI). As such, New Zealand horses are naїve to the virus and completely susceptible to infection. Disease models are one tool that can be used to examine the effectiveness of control strategies and can be used to initiate informed discussion regarding potential control options. In order to develop an EI InterSpread plus model, data were required regarding the New Zealand equine population. Data were collected via cross-sectional survey regarding the non-commercial horse population, through face-to-face interviews with stud managers and through the analysis of data regarding race meetings. Properties keeping horses for competition, recreation or racing were more likely to report a movement event than properties that did not. Movement events and the frequency of movement increased with increasing numbers of mares and stallions on a stud farm and with the presence of a shuttle stallion. There were significant differences between Standardbreds and Thoroughbreds travelling to race meetings and horses travelled further to attend premier race meetings. The level of biosecurity practiced was low and unlikely to be effective at preventing EI transmission during an outbreak. The disease model investigated three vaccination strategies in conjunction with movement restriction, compared to movement restriction alone. Additionally, the timeliness of vaccination strategies and enhanced surveillance were investigated. The results of the InterSpread plus model showed that the predicted length of an EI epidemic and the number of properties infected were fewer, if vaccination was implemented. The vaccination strategy that predicted the fewest number of infected properties, and the shortest epidemic duration, was implemented on day seven after official detection at a three kilometre radius around an infected property. This thesis highlights the complexity inherent in developing disease models to support decision making.