Invisible line 'protects Australia from bird flu'
Australia's best defence against an outbreak of avian influenza is an invisible line passing through the Indonesian archipelago between Bali and Lombok that birds are reluctant to cross, a team of zoologists says.
In the latest Ecology and Society journal, the Australian researchers say the so-called Wallace Line, which forms a distinct boundary between the Asiatic and Australian faunal realms, has to date protected Australia from the most recent bird flu outbreak.
The finding is part of an analysis the team undertook to determine the risk of highly pathogenic avian influenza epizootics, in particular the deadly H5N1, entering Australia through bird migration in the north.
However the five authors say the relative isolation of Australia cannot be assumed to be a complete barrier against the arrival of the deadly H5N1 strain that has claimed 245 human lives worldwide.
The team highlights West Papua, which lies on the Australian side of the Wallace Line, where H5N1 was found to be responsible for the deaths of 93 chickens in three villages in July 2006 as a possible pathway for the disease to reach Australia.
According to the World Health Organization, there have been 245 recorded human deaths from the H5N1 form of bird flu. More than 150 million birds have either died or been destroyed across Asia since the current outbreak began in mid-2003.
Currently the disease is only transmitted between poultry and humans who come in close contact with the diseased fowl.
However, health authorities fear the virus could mutate into a form that is transmissible between humans and lead to a global pandemic.
"To date Australia is the only inhabited continent not to have recorded high pathogenicity avian influenza since 1997, and H5N1 has never been recorded," lead author Professor Hamish McCallum, of the University of Tasmania, and colleagues say.
And the prevalence of avian influenza in wild birds is much lower in Australia than elsewhere. Since 2004, only 1% of more than 16,000 wild birds have tested positive for the disease.
Part of the reason the authors say is the "remarkably little avian migration" across the Wallace Line.
"The Wallace Line is a trenchant biogeographical border between the Australo-Papuan region and the rest of the world," says co-author Dr Leo Joseph, director of the CSIRO's Australian National Wildlife Collection.
"Most Australo-Papuan bird life reflects the long-standing isolation of the region. The big exception to this is the millions of shorebirds that come from Siberia every summer.
"But there is no evidence that waterfowl, which are the primary reservoir of avian influenza, move across the Wallace Line."
Migratory waterbirds, in particular many ducks and geese, have been implicated in spreading the virus.
The authors highlight the Trans Fly region, centred on the southern floodplains of New Guinea's Fly River, as a possible disease pathway because of the large number of waterbirds that move between this area and northern Australia.
However the Trans Fly region is almost 100 kilometres from the most recent outbreak of H5N1 in West Papua.
The authors add that "even if highly pathogenic avian influenza were to arrive in Northern Australia in migrating waterbirds, population density of humans, and thus domestic poultry is very low in this region".
But they point out that some species of waterbirds are known to be highly dispersive within Australia and could form links between the northern wetlands and southern wetlands close to major poultry production areas.
"Another potential concern is that avian influenza .. has been found in white ibis, which have increased dramatically in the last few years, particularly in association with humans," they say.
Joseph says follow-up research to fill gaps in knowledge that will improve the accuracy of risk mapping is already under way.
Co-author Dr David Roshier, of Charles Sturt University, is leading a team using satellite tracking to view the movements of up to 20 wandering whistling duck in Papua New Guinea.
Researchers are also undertaking population genetic studies to determine current and historical connections between bird populations, and using isotope ratios of elements in bird tissues such as feathers to track bird movements, Joseph says.