Analysis: The first sign of the arrival of lethal avian flu in New Zealand would likely be a wave of mysterious deaths among our native birds, a top virologist says, rather than in a human case.
While the announcement last week of two instances of avian influenza in Australia – one in a person who had travelled from India, the other on poultry farms – has prompted worry in New Zealand, the greater cause for concern is the ongoing outbreak among dairy cattle in the United States.
The strain of influenza virus detected in the Australian who returned from India is H5N1, but a different variant than the one behind a global explosion of cases in birds and now some mammals in recent years. The egg farm detections in Victoria, meanwhile, are of the H7N3 strain and similarly disconnected from the global outbreak.
“That was kind of like a locally adapted [virus]. That happens sometimes – there’s mutations in the influenza virus that cause disease and quite a limited outbreak. It’s not related to the one that’s running around the world,” Jemma Geoghegan, an evolutionary virologist at the University of Otago, told Newsroom.
In other words, there’s no reason to think the H7N3 outbreak could have public health ramifications. The H5N1 virus, meanwhile, has historically struggled to transmit between mammals since its discovery in the 1990s, so the human case in Australia poses little public health risk.
The concern for New Zealand is whether that might change, particularly now that there is strong evidence the virus has adapted to spread between dairy cattle in the United States.
Since 2020, partially unnoticed by the general public due to the high profile of the Covid-19 pandemic, a new variant of H5N1 has been tearing through wild bird populations. The virus has leapt repeatedly into domestic birds and wild and domestic mammals, leading to the deaths of more than 100 million animals through disease or culling.
There are two developments that raise the risk for New Zealand. The first is the dairy cattle outbreak in the United States.
“Preliminary genomic evidence from the outbreak among the cattle herds in the US suggests that this virus now appears to be transmitting from cow to cow and that’s really concerning,” Geoghegan said.
“The virus has acquired a genetic mutation to allow more efficient transmission between mammals and this is actually the first evidence of mammalian transmission of this virus. That is something that we haven’t seen before, in the 30-year history of this virus.”
As with Covid-19, which became better adapted to spread between humans and to avoid vaccine-induced immunity by repeated exposures, there are concerns H5N1 could continue to adapt to mammals as long as it spreads among them.
Pigs have traditionally been a potent host for adapting avian influenza viruses for human transmission – this was the process that led to the 2009 H1N1 swine flu pandemic. Geoghegan said researchers were most concerned about this as an avenue for turning H5N1 into a threat to human health.
One recent study, which has yet to be peer-reviewed, also found that the udders of cows have both the receptors used by flu viruses to enter human cells and bird cells. It is the co-location of these receptors in pigs that is thought to make them such potent mixers of influenza viruses.
“The fact that whole genomes of this virus have been pulled from store-bought milk [in the United States] does suggest that this virus can survive in a range of environments. Not that it would be infectious in milk but that it’s there is something that’s pretty worrying,”Geoghegan said.
The occasional spillovers into humans which have occurred since 1996 have seen about half of those infected dying of the virus, although there’s no guarantee the virulence of H5N1 would remain the same if it were to become transmissible between humans.
The second development that throws up red flags for New Zealand is the arrival of the global H5N1 outbreak in Antarctica. While this doesn’t pose a human health risk, the virus could still deal serious damage to our native bird populations as well as, potentially, agricultural livestock.
H5N1 has so far only been detected on the Antarctic Peninsula, which is virtually across the continent from New Zealand. But the virus is already highly mobile and the populations it has been found in – including penguins, seals and gull-like arctic skuas – are common across the landmass.
“Birds disperse quite far across Antarctica and we know they come up to the sub-Antarctic islands as well.”
That said, the detection of the virus in highly researched bird populations in Antarctica could mean we focus too much on that vector of approach. Geoghegan says it’s just as possible the virus is running rampant in the northern hemisphere sites where birds spend the winter before returning to New Zealand in the spring.
“Our northern hemisphere flyway sites, through southeast Asia and so on, we don’t have too much data about wild bird populations there.”
When Newsroom reported in-depth on the state of the H5N1 outbreak and New Zealand’s readiness for it last year, the Ministry for Primary Industries advised the virus was unlikely to arrive here on the wings of a migratory wild bird.
“We are isolated from other land masses, do not have migratory waterfowl pathways and have strong border biosecurity,” Biosecurity NZ’s chief veterinary officer Mary van Andel said at the time.
“A variety of migratory shorebirds and seabirds travel a long distance to return to New Zealand each spring, but due to the high mortality of HPAI viruses like H5N1, the risk for live infected species making the journey to arrive here is considered low. Together with DoC, Biosecurity New Zealand has sent AI screening kits to the Subantarctic Islands for testing to support reporting in case unusual mortality events are detected there.”
Now, Geoghegan isn’t so sure.
“I don’t think that statement is true anymore because the virus has changed. That was kind of the case then, but the virus has evolved and we’ve seen how the genetic changes in the virus have now allowed the virus to massively expand its host range. It can affect such a wide variety of birds, not necessarily causing severe disease,” she said.
That’s why Geoghegan is working with Te Niwha, the infectious diseases research platform jointly hosted by Otago and ESR, to sample birds throughout the country. Understanding how diseases spread to New Zealand and then among our wild birds is key to preparing for the arrival of H5N1.
Hundreds of samples from the sub-Antarctic islands and the North Island flyway sites where migratory birds arrive from the northern hemisphere have been processed by Geoghegan and her team so far.
“We’re trying to understand viral transmission among birds generally, so that we might be able to model how a new virus like highly pathogenic flu could be transmitted into the mainland and around as well,” she said.
“The first signs of the disease in New Zealand is probably going to be a bunch of dead birds, to be honest.”
