MORE than 50,000 layer hens will be killed because of the detection of an unidentified strain of bird flu at an egg farm near Maitland.
The Department of Primary Industries has put the farm under quarantine and is trying to determine if the virus has spread.
NSW chief veterinary officer Ian Roth said the department's "first response team" was at the farm to monitor the lockdown and the CSIRO was doing final checks to confirm the virus.
"The suspected virus is definitely not the highly pathogenic H5N1 strain that has gained worldwide attention, nor is it closely related to that strain," Dr Roth said.
"Australia has previously had a small number of avian influenza viruses, which were all quickly and successfully eradicated."
It is understood the property owners are co-operating and the egg industry's peak body, Australian Egg Corporation, has been advised.
Dr Roth said tracing and surveillance were under way and there was no indication, so far, that the disease had spread.
"Department of Primary Industries and the Livestock Health and Pest Authority are continuing surveillance and tracing to confirm the virus hasn't spread," he said.
"We currently have no evidence to suggest it has spread."
The H5N1 strain of bird flu can be transmitted from birds to humans and there are fears it could mutate and cause a pandemic, being transferred from person to person. To date, research has not shown that any other strain of the virus can be transmitted to humans.
* Avian influenza refers to influenza A viruses usually found in birds. They infect a broad range of avian species, and other species including humans, pigs and horses.
* There are many different strains of avian influenza virus but only a few cause severe disease in poultry and other birds, and even fewer cause infections in humans.
* Australia has previously had five outbreaks of avian influenza in poultry, all related to H7 viruses, with the last in 1997.
* The H5N1 virus is one strain of avian influenza, but Australia has never had it identified in poultry or humans.
* The H5N1 virus can cause severe infections in humans. By the end of 2010 there had been more than 500 human cases of H5N1 reported worldwide, with a death rate of more than 60per cent.
* Public health authorities are concerned that an H5N1 virus may undergo changes that allow it to spread easily between humans, which could cause a pandemic.
Source: NSW Health