The successful eradication of equine influenza from Australia was one of the greatest achievements of veterinary medicine in recent years, a recently published review suggests.
The review by Dr Romain Paillot, who is head of immunology in the Infectious Diseases Department at Britain’s Animal Health Trust, and Dr Charles El-Hage, from the Centre for Equine Infectious Diseases at the University of Melbourne, examined the use of a recombinant canarypox-based equine flu vaccine during the 2007 outbreak.
The pair, writing in the journal Pathogens, said it was the most extensive equine influenza outbreak observed in recent years.
Extraordinary measures were rapidly implemented in order to control and prevent the spread of the highly contagious disease, they said.
The control strategy involved stringent movement restrictions and disease surveillance, with emergency post-outbreak vaccination strategies.
Sixteen months after the first case and 12 months following the last reported case, Australia regained its equine influenza-free status with the World Organisation for Animal Health (OIE).
Australia had been free of the disease until August 2007, when the first case was diagnosed in New South Wales.
The outbreak originated from the importation of one or more sub-clinically infected horses from Japan, which was experiencing a flu outbreak at the time.
Paillot and El-Hage said these horses had either responded poorly to recent vaccination or were infected during the immunity gap, a period of low protective immunity that may occur in some vaccinated horses between the primary vaccination course and the first booster.
Australia’s horse population was naive to the infection, which meant the breach of quarantine at the Eastern Creek Animal Quarantine Station near Sydney and the subsequent virus escape led to a significant outbreak.
More than 76,000 horses were infected across 10,600 properties. Its rate of spread was reported in some cases to be around 1km to 1.5km a day in the absence of horse-to-horse or human-to-horse contact.
Following the initial spread of the flu virus that occurred at horse competitions in New South Wales and Queensland, an immediate 72-hour nationwide “horse standstill” was imposed. Within three weeks a zoning system was in place with varying levels of restrictions on horse movements.
An emergency vaccination programme was initiated in late September, some four weeks after the outbreak was declared. It involved 130,000 to 170,000 horses. The vaccination strategy included ring vaccination around in 10km wide vaccination buffer zones; predictive vaccination, which targeted horse populations posing strategic or economic risk to contribute to spread of the disease, such as thoroughbred racehorses and competition horses; and blanket vaccination, to maximise immunity in specific area.
Paillot and El-Hage said the virus was contained to about 3.5% of the Australian land mass. Provisional freedom from equine flu was declared on March 14, 2008, and full freedom on June 30, 2008.
In December 2008, 12 months after the last reported case, Australia regained its official equine-flu-free status from the OIE.
The pair traversed the choice of Merial’s ProteqFlu product, a live recombinant (canarypox) vectored vaccine. They said the successful use of this vaccine during the 2003 South African flu outbreak and the ability to differentiate infected from vaccinated animals through testing were important elements in favour of the canarypox-vectored vaccine.
“The importance and role played by emergency vaccination in Australia was debated, as the number of new infected cases was already decreasing at the time of vaccination, and natural protective immunity was increasing.
“However, models of the outbreak revealed that vaccine implementation; alongside biosecurity measures and movement restriction, were effective in the eradication of equine influenza in Australia.”
They noted that early vaccination is now considered to be a strategic and key control measure in case of future equine flu outbreaks in Australia. The current federally sanctioned plan involves ring vaccination around infected areas; predictive vaccination for high-risk enterprises and densely populated areas; blanket vaccination in specific and infected areas; and preventive vaccination in specific areas and populations to facilitate business continuity.
The pair said responses to vaccination and other control measures used in Australia had been rarely documented in horses with such detail before.
“In our opinion, successful eradication of equine influenza in Australia represents one of the greatest achievements of veterinary medicine in recent years,” they concluded.
The Use of a Recombinant Canarypox-Based Equine Influenza Vaccine during the 2007 Australian Outbreak: A Systematic Review and Summary
Romain Paillot and Charles M. El-Hage
Pathogens 2016, 5(2), 42; doi:10.3390/pathogens5020042