Analysis of horse movements and events during the 2007 outbreak of equine influenza in New South Wales, Australia.

OBJECTIVE: To analyse horse event and horse movement registration data collected between September 2007 and December 2008 during the outbreak of equine influenza in New South Wales, Australia. RESULTS: A total of 9356 events were registered, involving 504,382 horses and 242,952 riders. Registered horse movements totalled 224,084, involving 349,327 horses (excluding mobs) travelling 34.4 million km with an average of 154 km per journey. The number of recorded events and movements were low while movement controls were most stringent, then increased from December 2007 as restrictions were eased, to peak in April 2008 with up to 290 events and 15,730 movements weekly, after which registrations declined as the disease was eradicated. The main types of events registered were pony clubs (38%), race meetings and trials (17%), competition (13%), and clinics and lessons (11%). CONCLUSIONS: Registration of horse events and movements allowed movement controls to be progressively eased while retaining the ability to trace the movements of large numbers of horses if needed. The number of recorded events, movements and distances travelled confirms the highly mobile nature of the recreational horse industries, helps to explain the rapid and widespread dispersal of the disease before movement restrictions were imposed, and also demonstrates the value of those restrictions as a control measure. The data provide a quantitative snap-shot of horse events and movements, albeit distorted by the prevailing movement restrictions as well as by limitations in the data recording that should be addressed when developing traceability systems for horses in future.