Scientists have been growing increasingly concerned by the spread and evolution of H5N1 avian flu, which has killed tens of millions of poultry birds in four years and been detected in two dozen countries. Photo / 123rf
Scientists have been growing increasingly concerned by the spread and evolution of H5N1 avian flu, which has killed tens of millions of poultry birds in four years and been detected in two dozen countries. Photo / 123rf
The rapid spread of bird flu around the world has scientists increasingly concerned. What’s the risk to people, livestock and native species in Aotearoa New Zealand? Science reporter Jamie Morton explains.
What is avian flu?
It’s a type of influenza that naturally occurs in birds and spreads throughsaliva, mucous and faeces. The type at the centre of global concern, H5N1, has now been formally detected in nearly 10,000 wild birds and more than 90 million poultry birds.
It’s led to the slaughter of more than half a billion farmed birds worldwide, while wild bird deaths are estimated to number in the millions.
So far, it’s spread to every region of the planet except Oceania - meaning it’s not in New Zealand yet.
Last year, it was confirmed the virus had reached as far as Antarctica, with tests confirming H5N1 in dead skuas found near an Argentine polar base on the Antarctic Peninsula.
Why are scientists concerned about its evolution?
The virus was first noted back in the 1990s, but since 2021, scientists have observed mutations that have allowed it to dramatically expand its host range.
“It doesn’t just infect certain types of wild birds anymore, but a range of hosts - and that has enabled it to spread to geographic regions where it’s never been found before,” Otago University evolutionary virologist Professor Jemma Geoghegan said.
Otago University virologist Professor Jemma Geoghegan.
More than two dozen mammal species have also been infected, including red foxes in Europe, cattle in the US, wild bears in Canada, minks in Denmark, and seals and sea lions in both hemispheres.
How worried should we be about its spread to cattle?
It’s still unclear how the virus showed up in three-dozen outbreaks among dairy herds in the US - potentially through exposure to infected birds - but Geoghegan said evidence suggests it was now being passed from cow to cow.
That’s concerning, given livestock like cows and pigs could act as “mixing vessels” to evolve new strains that could ultimately infect humans.
“In New Zealand, there is a lot more livestock here per capita than anywhere else,” Geoghegan said.
“We don’t have the virus at the moment, but if it was to travel here and get into our livestock, that would be very concerning.”
What threat does it pose to humans?
Instances of people being infected by bird flu have been rare - it’s been reported in just a few hundred people - but the case fatality rate is higher than 50 per cent.
However, the World Health Organisation (WHO) and other agencies consider the current risk to humans to be low.
Geoghegan said it was possible HN51 might not evolve to spread between humans, but its expansion into new countries and other mammalian species “provides more opportunity for that to eventuate”.
Geoghegan said the virus appeared to have been circulating in US cattle for a month before it was detected.
“The fact this virus is on every continent apart from Oceania means I’d be surprised if it’s not in other livestock farms and animals that we just don’t know about.”
Could bird flu reach New Zealand?
The biggest risk for the virus reaching our shores was through migrating birds - including the bar-tailed godwit, red knot, ruddy turnstone and Pacific golden plover - either from Antarctica or the north.
The bar-tailed godwit.
For that reason, Geoghegan and colleagues recently began carrying out sampling among sea, shore and water birds, including “flyway” sites where birds typically enter the country.
The team is also investigating how the virus could transmit among birds here, and methods to monitor it better and faster.
What do we have in place to prevent and control its spread here?
The Ministry for Primary Industries (MPI) has systems aimed at preventing it from arriving here through other pathways and detecting suspected cases early.
In the event of an incursion, Biosecurity NZ would take the lead and co-ordinate a unified response with the Department of Conservation (DoC) and the Ministry of Health.
MPI says any actions, such as movement control, vaccination or depopulation, “would depend on the infected species and location”.
What would bird flu mean for our native species?
“The vast majority of our native species are birds and have never been exposed to a virus like this before,” said Geoghegan, adding it could pose a potential extinction threat to some especially endangered species if their populations became infected.
A bird flu vaccine is being trialled in takahe and other species. Photo / Corelia Schulz, Dreamstime
The DoC acknowledges options would be “limited” - and the best approach would be to have healthy populations of native species separated across multiple locations.
Vaccination might also offer a way to protect some core breeding populations in captivity.
A trial was under way to test a bird flu vaccine on takahē, tūturuatu [shore plover], red-crowed kākāriki, kakī [black stilt] and kākāpō.
What about vaccines for people?
Unlike with Covid-19, scientists believe a vaccine could be rolled out relatively quickly, with two options at the ready.
Most developed nations - including New Zealand - have stockpiled doses closely matched to avian flu.
The Ministry of Health has also been preparing a response plan for a potential bird flu pandemic.
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.
