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
Bird flu recently entered Australia - is it just a matter of time before it hits in New Zealand too? A widely-spreading strain poses a major threat to our endangered wildlife and there are urgent questions about its potential to infect us too. Science reporter Jamie Morton putseven burning questions about bird flu to Otago University evolutionary virologist, Professor Jemma Geoghegan.
But the reason why everyone is talking about it now is a specific strain – the H5N1 variant - which has changed genetically so it can infect a much broader host range.
We know that RNA viruses are always evolving, but these mutations have adapted it to affect a huge number of different bird species.
It’s also allowed it to spread to places it’s never been before – that variant is now everywhere except Australasia – while maintaining a high mortality rate.
So, it’s a huge problem for wildlife and animal health, and now we’ve seen its potential to jump to cattle and spread between cows – something we’ve never seen before with this virus.
Why is the strain’s recent leap into cattle so significant?
Since bird flu first emerged, we’ve known of more than 800 human cases – but these have always been in humans in direct contact with infected birds.
There have also been spill-over events involving other mammals - seals, sea lions, dolphins and minks - where the virus has jumped from birds. In the last few years, these have increased dramatically.
Thousands of marine mammals have sometimes become infected at once, but evidence suggests these outbreaks have always been tied to a common source of infection.
However, the virus’ recent jump into cattle in the US seems to have been caused by a genetic change that has made the virus transmissible between cows.
We have a lot of dairy cattle in New Zealand, and if this virus migrated here, it could be a huge problem for us.
Importantly, although the virus can and has been detected in store-bought milk in the US, pasteurisation means it’s not infectious and makes it very unlikely that you can get infected by drinking milk.
Last week, we learned bird flu had spread to Australia - our closest neighbour. What does that mean for New Zealand?
In Victoria, there has been a case of H7N3 in poultry, which evolved locally from low-pathogenicity strains in Australia.
The other case involved a child who’d travelled from India to Australia in March, and who was diagnosed with H5N1.
Although it’s H5N1 and the same subtype, it’s a different lineage to the specific strain that we are more concerned about – and that one still hasn’t made it to Australia.
This virus has usually been introduced to new places by wildlife and there’s not a lot that you can do to keep it out, especially considering the high pathogenicity and broad host range of this one.
But detecting it early is key, so you can try to control its spread and limit the destruction it might have here.
In terms of the tools that we have for informing decision-making, I think we learned a lot during Covid-19, and we must maintain that capability and capacity.
This time around, we are looking at a disease that primarily infects animals, so the government agencies involved in the response will be different.
Why is the danger to our wildlife so high?
Most of the birds in New Zealand have never been in contact with avian influenza virus.
This strain is very pathogenic, so it could very well be catastrophic, as it has been in other areas of the world.
More than 80 per cent of our birds are already in danger, so we risk having whole species and populations wiped out if it does arrive here.
University of Otago evolutionary virologist Dr Jemma Geoghegan.
And what about the threat to humans?
There’s currently no evidence that the virus can spread between humans.
The fact it’s spreading between cows is quite alarming, because cows, like us, are mammals.
But the upper respiratory tract cells of cows are very different to our own, so the virus would still have to undergo a lot of genetic change to become transmissible between humans.
If the virus got into pigs, that would present a risk to humans very different to the one we have now.
At the moment, there’s a fairly low risk for people who don’t have contact with birds, and there are already potential human vaccines for bird flu that can be quickly produced.
What can we all do to help?
The most important thing is to be on the look-out for diseased or dead wildlife – especially birds or marine mammals – and report them to Biosecurity New Zealand at 0800 80 99 66.
Even if it’s just one bird, it’s still worth reporting, because if this virus is rapidly detected, it could help us avoid a much bigger outbreak.
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.
