Bird flu: do humans get it (and do I need to hard-boil my eggs)?
Avian influenza has again been found on Victorian poultry farms. It’s not the strain spreading worldwide killing birds, cats and elephant seals – and infecting people – nor last year’s variant that caused national egg shortages. But you do need to understand the concerns.
For many of us bird flu only registers as an issue as we wander past supermarket shelves stripped of egg cartons. But there is much to understand, and a deal to fear, about the potential impact of avian influenza into the future.
So with news of fresh cases of bird flu on three Victorian chicken farms, just days after the Albanese government declared Australia had eradicated a series of outbreaks during 2024 and was now virus-free, let’s take a dive into what’s going on.
What is bird flu?
Back to basics. Bird flu is caused by the avian influenza virus, of which there are many different strains out there. Most are “low pathogenic”, which means they have no clinical effects. They are part of the natural viral load of wild birds, their natural hosts. They are most commonly found in ducks, geese, and shorebirds, who spread them far and wide.
This is in contrast to highly pathogenic strains, which can lead to mass deaths or serious illness. Historically, these viruses were limited to poultry, where they evolved. In chickens, disease signs include diarrhoea, breathing difficulties, swollen heads or extremities, nervous signs such as shaking, or purple patches on legs or skin.
The virus tends to be quick-spreading because of the proximity of the birds to each other, and often fatal. More recently, one of the strains of high-pathogenicity avian influenza has jumped into wild birds, causing an animal pandemic. And it has infected some humans as well.
There are two “subtypes” of high-pathogenicity avian influenza causing concern at the moment: H5 and H7, both with serious consequences.
Dangerous strain #1 – H7
An H7 subvariant, H7N8, is what authorities are looking to contain and eradicate on three poultry farms (so far) in Victoria. The farms have been isolated in a bid to limit the spread.
This particular H7 strain is genomically different from the one that spread into 16 properties across NSW, Victoria and the ACT, including 11 poultry farms, in three outbreaks last year.
“When you think that there were three outbreaks in 2024, and prior to that only eight outbreaks of H7 bird flu dating back to the 1970s, you can see why this is being taken so seriously,” says Frank Wong, senior research scientist at CSIRO’s Australian Centre for Disease Preparedness.
Dr Wong says there is little option for authorities but to “depopulate” poultry farms where outbreaks occur, and last year’s cases saw more than two million chickens killed to contain the virus’s spread. Hence the current empty egg shelves, but more on that later.
The current outbreak in Victoria emerged just four days after the Albanese government declared Australia free of bird flu, having spent months working to eradicate the virus and ensure the safety of the poultry industry and the farms affected in 2024.
Dangerous strain #2 – H5N1
But while H7 strains of bird flu are worrisome, an even greater concern is the H5N1 strain, specifically the most recent H5N1 clade 2.3.4.4b variant.
This latest H5N1 variant has the world watching. It is spreading fast in epidemiological terms. And it is proving lethal for the species of birds and mammals exposed to it. Already more than 350 species of wild birds and more than 50 species of mammals have been infected.
It has reached into dairy farms, into zoos, household pets, and into some wild animal and bird populations with devastating effects. It has infected species such as sea lions and elephant seals, which may eat infected birds and then transmit it to each other because they live so close to each other.
“The consequences are likely to be catastrophic,” says Michelle Wille, a virus ecologist based at the University of Melbourne’s Centre for Pathogen Genomics.
“For instance in Peru, 40 per cent of all Peruvian pelicans have died from the virus. These are huge numbers and it shows the virus is potentially devastating for wildlife.”
She also points to Argentina, where 18,000 Southern Elephant seals died after becoming infected, almost all between one and two weeks old.
In the US, cattle farms have been affected right across the country. The latest data from the Centres for Disease Control shows there have been 972 bird flu cases in cattle across 17 states.
And The Wall Street Journal reported this week that domestic cats were testing positive for bird flu and becoming seriously ill or dying.
It points to research in December that found 10 domestic outdoor cats had died of avian influenza in South Dakota. While it wasn’t clear how the cats had been infected, some of the bodies were found with feathers around them.
Dr Wille is just back from a trip to Antarctica, and confirmed H5N1 2.3.3.4.b has made it there.
In fact, Australia is the only continent the virus hasn’t reached, but Dr Wille believes it is just a matter of time.
“There are three potential routes for arrival into Australia, all hingeing on migratory birds. One is the long journey from the northern hemisphere of millions of birds, the second might be Australian ducks journeying to Indonesia or PNG and back and there’s an increasing chance they may come from the south via Antarctica.”
“I think it’s highly likely this virus will arrive at some point. The fact we are an island continent won’t save us,” Dr Wille says.
Australian governments are alive to the threat, and have ramped up their preparedness plans as this variant spreads across the globe.
Last year, the federal government announced an additional $100m investment to “strengthen surveillance, preparedness and response capability and mitigate the impacts of a potential H5 bird flu outbreak on Australian agriculture, environment and human health.”
Can I catch it? And will it kill me?
First question first. Yes, humans can catch avian influenza. It is rare, but possible.
The most likely way for a human to catch bird flu is through close contact with infected birds, their faeces or feathers.
This spillover effect is why farm workers are at increased threat, and why they have specific advice about the need to wear PPE and be thorough with their hygiene when dealing with infected stock.
Travellers to countries where there have been outbreaks of H5N1 bird flu are advised to avoid poultry farms and wet markets.
Another risk factor is drinking “raw”, or unpasteurised, milk.
So will it kill me?
Dr Wong says people who do end up infected with the current strains of bird flu “commonly have only mild symptoms such as conjunctivitis or mild respiratory issues, and many have no symptoms at all, though there have been a small number of severe cases”.
“And humans can’t pass it to humans,” he says.
But previous strains of H5N1 have been much more lethal, with symptoms including pneumonia and encephalitis.
Dr Wille said that across the decades, around 40 to 60 per cent of those humans worldwide infected with all variants of H5N1 have died.
“This latest strain does appear to be milder in its effect on humans, though we need to watch out for future mutations,” she says.
US scientists are starting to become more concerned about the ability of the virus to mutate into variants that are more easily transmissible to, and between, humans.
“If the virus figures out a way to adapt and start transmitting between humans, infections in the general population could go up exponentially overnight,” Scott Hensley, a professor in the microbiology department at the University of Pennsylvania, told the WSJ.
“This is a major threat right now,” Professor Hensley says. “We know that it’s only one or two mutations away from leading to very severe disease. And influenza viruses acquire mutations all the time.”
Seventy people in the US have contracted the H5N1 strain of bird flu. Dairy and poultry farm workers are at biggest risk. Humans have been infected, though very rarely, through interaction with other animals, including one case when a person was exposed to an infected cat at an animal shelter in New York City.
The one reported case of H5N1 bird flu in Australia last year was a two-year-old child who brought it in from overseas. She spent some time in hospital before recovering. In the US a man has so far died with the virus, though it is understood he had a range of comorbidities.
What’s that got to do with the price of eggs?
As in the US, responding to an outbreak is usually done through a benignly titled “depopulation program”.
Last year, more than 100 million chickens were euthanised in a bid to stop the further spread of bird flu, and in Australia around two million were killed after the 2024 outbreaks.
While the populations regenerate, egg production has slowed, leading to shortages on the shelves. The two main grocery chains continue to impose box limits on egg purchases.
And the price of eggs has jumped, both here and in the US, where they have reached a record high. According to the Australian Bureau of Statistics, the price of eggs rose 11.2 per cent in the last three months of 2024. The latest outbreak will likely ensure no alleviation in price any time soon.
But are eggs safe to eat? Should I hard-boil them?
There have been no reported cases of people getting infected with bird flu from eating food, and the advice from the Australian Centre for Disease Control is clear on this.
“Bird flu is not a food safety concern for consumers,” it advises. “All food products in Australia must meet strict food safety production requirements before entering the commercial food chain. This includes testing for diseases like bird flu during outbreaks.
“There is no evidence that people can be infected with bird flu by consuming meat or eggs prepared in line with normal safe food handling practices.”
The NSW Food Authority also suggests “not eating cracked or dirty eggs, avoid eating raw eggs, and to cook poultry thoroughly”.
It notes that the chance of bird flu entering the human food chain is “very low”.
“This is because there are measures in place to prevent sick animals from entering the food chain. Also, avian influenza usually stops birds laying eggs, and the few eggs that are laid generally would not get through egg washing and grading because the shells are weak and irregularly shaped.”
But it does suggest carefully cooking poultry products at temperatures above 70C, which will kill any virus.
And the US Centres for Disease Control recommends cooking eggs to a minimum internal temperature of 74C in order to kill bacteria and viruses, including bird flu and salmonella.
So what does this mean in practice? Well if you want soft boiled eggs, they will need to be cooked below 70C. Same with poached eggs that have a runny centre.
But this is an issue of risk-reward, bearing in mind the strict hygiene standards in Australian food production and handling. The approach recommended by Eggs Australia (the advocacy body representing egg farmers) and the New Zealand Food Safety body is to ensure the white is completely set and the yolk has begun to thicken.
