Bird flu at Mainland's Otago farm, no disease yet on other farms

Following the detection of a high pathogenic strain of avian influenza, H7N6, at one of Mainland Poultry’s commercial egg farms in rural Otago earlier this week, Biosecurity New Zealand has conducted initial testing and monitoring at the Dunedin-based company’s other farms in New Zealand.

While extensive work continues, there are no signs yet of bird flu on the company's other chicken farms in Otago, Biosecurity New Zealand has announced. About 1000 samples were received for testing at the Ministry for Primary Industries’ (MPI) Wallaceville laboratory in Wellington, and it is prioritising analysis according to assessed risk.

“The first batch of results, and ongoing monitoring at Mainland Poultry’s properties that have links to the Hillgrove site, show no signs of new disease at this stage, which is promising. However, we are continuing rigorous testing as the disease has an incubation period,” Biosecurity New Zealand’s deputy director-general Stuart Anderson said.

Culling continues

“There have been no signs of production loss or ill birds at Mainland Poultry’s five other properties to date, and we will keep monitoring closely.”

Anderson said samples from a smaller free-range chicken farm near Dunedin are being closely analysed and test results are expected soon.

“Testing is normal in biosecurity responses where illness is identified. We acknowledge this is an extremely difficult time for the affected farmers, through no fault of their own, and we are working to support them.”

Anderson said work is continuing to support Mainland Poultry to humanely cull chickens in two of its sheds on one of its Otago farms.

“The material is being taken to a secure landfill in Southland, which is equipped to take this kind of waste.

“The cull is using the industry standard practice of CO₂ containerised gas, which farms regularly use to euthanise chickens.

“The incubation period for the virus is usually 3 to 14 days, with a possibility up to 21 days, so testing will continue over the next 2 to 3 weeks,” Anderson said.

Situation management

Biosecurity New Zealand has increased its presence on the ground in Otago and has set up a regional control centre to manage the situation.

Professor Jemma Geoghegan, Virologist, University of Otago, said the detection of H7N6 at a New Zealand farm is worrying; however, it is not the H5N1 strain that she and her colleagues are most worried about.

“Usually the H7 subtype is low pathogenic and is found in wild birds without causing disease. On some rare occasions, these viruses can spill over to poultry and evolve to become high pathogenic where they cause severe disease.

“This is what we saw happen in Australia a few months ago too. With chicken farms in such close proximity to wildlife, these sorts of spillovers are always a risk.

“The H7 subtype, while it has infected humans before, doesn’t spread very easily between them so this is low risk for public health.”

Early detection

Nigel French, Distinguished Professor of Infectious Disease Epidemiology and Public Health, Massey University, said, “While there is a strong focus on early detection of the globally circulating ‘panzootic’ H5N1 strain of bird flu, MPI and infectious disease experts in Aotearoa have always been aware of the possibility of a local ‘conversion event’.

“Rather than importation through migratory wild birds, this is where a low pathogenic strain (LPAI) can develop into a high pathogenic strain (HPAI), locally, in a flock infected with the low pathogenic strain. LPAI strains are known to circulate in NZ wildlife, so this was always a possibility that needed to be prepared for.

“Such an event happened in Victoria, Australia earlier this year — that was a strain of H7N3 that most likely entered the flock through wildlife. This detection was followed by further detections of other strains of HPAI in other states, all most likely local conversion events.

“If the affected farm has been detected early there is a good chance this outbreak will be contained. However, vigilance and raised awareness for avian influenza is needed, whether it is for the globally circulating H5N1 strain, or locally evolved strain.”

Image credit: iStock.com/Gins Wang