What’s the risk of a bird flu outbreak in humans?

Thursday, 25 April 2024

Preparations are underway for a possible outbreak, with various ministries working on a response plan that can be implemented quickly.

Bird flu has been quickly making its way around the world over the last four years, killing animals across multiple continents.

New Zealand has escaped an outbreak so far, but should it turn up, what is bird flu? And should we be concerned about it?

What is bird flu and what is the new strain?

Bird flu, also known as avian influenza, or HPAI, is a type of flu caused by the influenza A virus. It is similar in nature to other types of flu where a virus strain attaches itself to a host.

Wild aquatic birds are a natural reservoir for influenza viruses and have existed as long, or longer than birds, so millions of years.

There are many types of bird flu, but the strain that is spreading globally is the highly contagious H5N1 strain, which was first discovered in 1997.

This strain primarily spreads among birds and poultry, but can infect humans.

H5N1 is endemic in many bird populations, especially in Southeast Asia and there were over 100 outbreaks of the virus between 2006 and 2009 mainly centred in Asian countries.

From 2003 to 2024, there have been 889 cases and 463 reported deaths in humans due to H5N1. This puts the case fatality rate for humans at 52%.

Workers place dead chickens into plastic bags after they were killed at the Wholesale Poultry Market in Cheung Sha Wan, Hong Kong.

Why does this matter?

A new highly pathogenic strain has emerged in recent years and the mutations that have accumulated in this particular strain have allowed this version of the virus to infect a broad range of hosts.

This current outbreak began in 2020 and has continued to spread globally. H5N1 is now found in Asia, Europe, the Middle East, Africa, North America, South America, and even Antarctica.

The latest outbreak of bird flu has spread to cows.

The virus has so far not been detected in Australia, New Zealand, or the Pacific.

Experts have called this latest outbreak panzootic (animal pandemic) due to its global impact and how the virus has infected more than 200 species of wild birds.

It has also spilled over to mammalian hosts as well, including marine mammals, cattle and even cats. This has concerned the World Health Organisation who said this could increase the risk of the virus infecting humans.

The virus has killed millions of birds, including chickens around the world.

Professor of Evolutionary Virology at the University of Otago Jemma Geoghegan says it is hard to say if the virus could spread between humans at this stage.

“There's never been evidence to suggest that it has evolved those key mutations to allow it to become airborne, or likely to pass between us. But there's been some experimental work to suggest that only a few mutations are needed to allow that.”

Geoghegan said the more cases of the virus spilling over to mammalian hosts, the more likely those hosts will provide a vessel for mammal to mammal transmission.

Is it likely to come to New Zealand, are we prepared?

New Zealand’s native birds could be impacted if bird flu arrived here.

Yes there is a high chance it will come to New Zealand, and in fact one professor says it is not if, but when. Distinguished Professor of Infectious Disease Epidemiology and Public Health at the University of Otago Nigel French says the worry is it coming up through Antarctica or via the flight path of birds.

“There's various ways we could get it, and so any surveillance has to be mindful of that. It's one of those things, it could arrive tomorrow, or it could be years before it arrives,” French said.

Preparations are underway for an outbreak, and a spokesperson for the Ministry of Health told Stuff that the Ministry of Health, the Department of Conservation, and the Ministry of Primary Industries are working together on a response plan that can be implemented quickly if the virus were to reach New Zealand.

In a statement they said It is very rare for humans to be infected and because of this, they do not anticipate a major impact on the healthcare system.

The virus has spread to mammals such as cows, but human to human transmission has not occurred yet.

In preparation for an outbreak, however, the ministry said they are reviewing their testing infrastructure to ensure they are prepared to detect cases of the virus in humans.

They are also preparing updated health guidance, both for the public and for specific groups who might be exposed to infected birds and marine mammals in the event that the virus is found in New Zealand.

For now, the ministry is advising people who are exposed to wild birds or marine mammals to maintain good hygiene, wash their hands regularly, and avoid contact with sick or dead birds.

They added that travellers overseas should avoid poultry and fur farms and contact with animals in live markets. Returning travellers should contact their doctor if they feel unwell and inform them of their travel history.

DOC are also already trialling vaccines on a bunch of endangered native birds and French said we wouldn’t be in the same situation as Covid in terms of there being no vaccine initially.

A man collects eggs from chickens in holding pens in Cambodia.

“The emphasis would go on making sure the current vaccine was fit for purpose and appropriately distributed. So in New Zealand, we would have to make sure that we would have access to available vaccines.

What are the experts saying?

Experts remain concerned about what an outbreak could do to our native birdlife, especially given many of these species have not encountered bird flu before.

“It is likely if this highly pathogenic strain of bird flu was to come here it would have a really devastating effect on wildlife. And then there’s other things to consider, like we have a really big agricultural livestock industry as well,” Geoghegan said.

We are not really going to be able to stop it, but we can, if we catch it early, potentially prevent it from spreading to other hosts and other geographic regions around the country and also infecting people. So you know, really quick alert systems are needed to be able to stop it as soon as it does arrive,” she added.

“In terms of our native bird life where we have some really small populations, if it were to get into those populations it could potentially wipe them out. It could result in wild bird extinctions, particularly among shorebirds,” French said.

As for it being the next pandemic, well it already is in some respects.

“It's a pandemic among wild birds or wildlife at the moment,” Geoghegan said. “Whether it becomes a human health issue is a sort of wait and see.”

French said there are concerns it could develop into a pandemic much like Covid. “The World Health Organisation is thinking that the next pandemic could be an influenza pandemic as has happened before, and there is increasing concern that highly pathogenic avian influenza could cause a pandemic. There's a number of events that need to happen before that could happen though.”