Major study: What scientists just learned about bird flu in NZ

When researchers analysed 16 years of Ministry for Primary Industries sampling, covering some 19,000 wild birds, they found the key carriers of avian flu within New Zealand weren’t migrating seabirds, but mallard ducks.

As a fast-evolving type of bird flu sweeps the world, a new study has revealed more about lower-risk avian flu strains that have long been in New Zealand.

The H5N1 strain - not yet detected in New Zealand - can cause severe infection and has been responsible for tens of millions of bird deaths around the world.

Its recent jump to cattle and other mammals has put health agencies - in New Zealand and globally - on high alert.

Local scientists say H5N1 could devastate populations of threatened native bird species if it turned up here.

And in a double-threat for New Zealand, it could also cause major headaches for our primary sector.

Its most likely route into the country is through migratory birds, like bar-tailed godwits and red knots, flying in from the north or south from Antarctica - where it was detected earlier this year.

Now, a just-published analysis has shown that - at least up until now - the risk of migrating birds bringing risky strains of bird flu has been low.

Its authors said that, even if shorebirds flying from Alaska were infected before departing, it remained “uncertain” they could complete an 11,000km non-stop flight to New Zealand, or maintain the virus within them the whole way.

But red knots that had stop-overs in China, Southeast Asia and Australia posed a different risk, they said, as they could become infected with new viruses on the way.

The risk could also shift as rapidly-mutating strains like H5N1 widened their range across species and regions.

When the researchers analysed 16 years of Ministry for Primary Industries data for avian flu, covering some 19,000 wild birds, they found the carriers most identified by the sampling weren’t migrating birds, but mallard ducks.

Annual prevalence of low-pathogenic bird flu strains – or those less likely to cause severe infections in birds – among the ducks tested was shown to range as high as 83 per cent.

Biosecurity New Zealand’s virology team manager, Anastasia Chernyavtseva, said the genetic analysis suggested these viruses had been circulating here for decades, with no evidence of recent introductions.

However, she added, ongoing surveillance of wild birds was “increasingly important” given rapid shifts in bird flu overseas.

Infectious disease expert Distinguished Professor Nigel French said that, although they were the most likely route, migrating birds weren’t the only path for higher-risk strains to turn up here.

One was endemic strains being “converted” into more infectious ones, through subtle genetic changes within the virus.

“This has happened on multiple occasions in multiple locations over decades, and the number of recorded ‘conversion events’ has increased over time.”

That also proved to be the cause of a recent outbreak in Australia, where hundreds of thousands of chickens were slaughtered to control spread of an H5N1 strain closely related to the one sweeping the world.

French said close monitoring remained key to being able to detect and respond to any incursion quickly.

“The public of New Zealand can also play a crucial role in surveillance by knowing what to look out for and what to do if they find potential signs of bird flu in wild birds, wild mammals or domestic poultry.”

Jamie Morton is a specialist in science and environmental reporting. He joined the Herald in 2011 and writes about everything from conservation and climate change to natural hazards and new technology.