New Zealand enjoyed few restrictions on horse movements between the two countries before the outbreak.
MAF Biosecurity activated its Exotic Disease Response Centre when it became clear a number of horses had been imported into New Zealand before Australia realised the disease had been introduced to that country.
A just-released report outlines the New Zealand response to the initial threat of the Australian outbreak - dealing with the possibility the infection may have been introduced.
The location of horses imported from Australia during the crucial August period last year.
The report noted that the disease was suspected in a clinically sick horse at the Eastern Creek Quarantine Station, near Sydney, on August 17.
The disease was confirmed on August 20 and biosecurity officials in New Zealand were notified of this case on August 23. Sick horses were also seen on August 22 outside of quarantine at the Centennial Parklands Equestrian Centre (CPEC) adjoining Centennial Park in central Sydney.
These horses were confirmed on August 24 as having equine flu and Biosecurity NZ was notified of the outbreak the next day.
"Prior to this incursion, Australia and New Zealand were the only major horse breeding countries of the world to have remained free of EI.
"Because of the relatively free movement of horses between Australia and New Zealand before notification of the EI outbreak, it was important to assess whether equine influenza virus had been inadvertently introduced into New Zealand.
On the day of notification Biosecurity NZ stopped all imports of horses from Australia and increased border controls for horse equipment and horse semen.
That same day the Exotic Disease Response Centre was activated at the Investigation and Diagnostic Centre at Wallaceville, Upper Hutt.
"At this time the date of EIV release from Australian quarantine was unclear but considered unlikely to have occurred before August 1, 2007. Consequently, the objective of the EDRC was to determine the EI status of all equine imports from Australia during August 2007.
A complete list of 96 imported horses was obtained from several sources: MAFBNZ import group, trans-Tasman import companies, and lists supplied from Equestrian Sports New Zealand, New Zealand Thoroughbred Racing and Harness Racing New Zealand.
A response team phoned New Zealand owners of the horses on the day Biosecurity NZ was notified of the Australian outbreak.
Horse owners were asked about the health of the horses and other equines that had been in contact with it.
The horse owners were asked voluntarily to keep the imported horses and any horses that had been in contact with them separate from other equines, and remove them from paddocks adjoining boundary fences.
All horses imported from Australia during the previous 24 days, and their contacts, were examined and tested, as were any horses with respiratory disease. No horses had clinical signs consistent with equine influenza and all horses tested were negative to the virus.
Tracing was also undertaken to clarify the location of source farms in Australia, the network of contacts within Australia and New Zealand, and infected zones in Australia.
Risk management criteria were developed to evaluate the risk posed by imported horses and the property visits were prioritised accordingly.
The New Zealand EI response plan completed by MAFBNZ and ratified by the New Zealand Equine Health Association (NZEHA) in 2006 was used as the basis for procedures and data collection forms for farm visits.
The 96 imported horses had come in 16 consignments during August. Fifty-five horses arrived before August 15 (lower risk) and 41 thereafter (higher risk).
The horses had been delivered to 41 North Island and 12 South Island properties.
All veterinary visits and transfer of samples to the Animal Health Laboratory were completed by September 1. Between August 31 and September 3 all owners were informed that horses had tested negative.
The Exotic Disease Response Centre was stood down on September 3.
The report said: "Initially Australian authorities identified 8 August 2007 as the most likely start of the risk period. Biosecurity NZ took the precaution of adding a buffer period and investigated the EI status of all horses imported from 1 August 2007.
"This approach proved to be well founded as Australian epidemiological assessment indicated that the entry of EIV into NSW may have occurred as early as 3 August 2007."
It went on: "The threat of equine influenza virus introduction remains a constant risk to the New Zealand horse population."