This article is republished from The Conversation under a Creative Commons license. Read the original article.
Bird flu has been detected in a pig in the US. Why does that matter?
C Raina MacIntyre, UNSW Sydney and Haley Stone, UNSW Sydney
The United States Department of Agriculture last week reported that a pig on a backyard farm in Oregon was infected with bird flu.
As the bird flu situation has evolved, we’ve heard about the A/H5N1 strain of the virus infecting a range of animals, including a variety of birds, wild animals and dairy cattle.
Fortunately, we haven’t seen any sustained spread between humans at this stage. But the detection of the virus in a pig marks a worrying development in the trajectory of this virus.
How did we get here?
The most concerning type of bird flu currently circulating is clade 2.3.4.4b of A/H5N1, a strain of influenza A.
Since 2020, A/H5N1 2.3.4.4b has spread to a vast range of birds, wild animals and farm animals that have never been infected with bird flu before.
While Europe is a hotspot for A/H5N1, attention is currently focused on the US. Dairy cattle were infected for the first time in 2024, with more than 400 herds affected across at least 14 US states.
Bird flu has enormous impacts on farming and commercial food production, because infected poultry flocks have to be culled, and infected cows can result in contaminated diary products. That said, pasteurisation should make milk safe to drink.
While farmers have suffered major losses due to H5N1 bird flu, it also has the potential to mutate to cause a human pandemic.
Birds and humans have different types of receptors in their respiratory tract that flu viruses attach to, like a lock (receptors) and key (virus). The attachment of the virus allows it to invade a cell and the body and cause illness. Avian flu viruses are adapted to birds, and spread easily among birds, but not in humans.
So far, human cases have mainly occurred in people who have been in close contact with infected farm animals or birds. In the US, most have been farm workers.
The concern is that the virus will mutate and adapt to humans. One of the key steps for this to happen would be a shift in the virus’ affinity from the bird receptors to those found in the human respiratory tract. In other words, if the virus’ “key” mutated to better fit with the human “lock”.
A recent study of a sample of A/H5N1 2.3.4.4b from an infected human had worrying findings, identifying mutations in the virus with the potential to increase transmission between human hosts.
Why are pigs a problem?
A human pandemic strain of influenza can arise in several ways. One involves close contact between humans and animals infected with their own specific flu viruses, creating opportunities for genetic mixing between avian and human viruses.
Pigs are the ideal genetic mixing vessel to generate a human pandemic influenza strain, because they have receptors in their respiratory tracts which both avian and human flu viruses can bind to.
This means pigs can be infected with a bird flu virus and a human flu virus at the same time. These viruses can exchange genetic material to mutate and become easily transmissible in humans.
The Conversation, CC BY-SA
Interestingly, in the past pigs were less susceptible to A/H5N1 viruses. However, the virus has recently mutated to infect pigs more readily.
In the recent case in Oregon, A/H5N1 was detected in a pig on a non-commercial farm after an outbreak occurred among the poultry housed on the same farm. This strain of A/H5N1 was from wild birds, not the one that is widespread in US dairy cows.
The infection of a pig is a warning. If the virus enters commercial piggeries, it would create a far greater level of risk of a pandemic, especially as the US goes into winter, when human seasonal flu starts to rise.
How can we mitigate the risk?
Surveillance is key to early detection of a possible pandemic. This includes comprehensive testing and reporting of infections in birds and animals, alongside financial compensation and support measures for farmers to encourage timely reporting.
Strengthening global influenza surveillance is crucial, as unusual spikes in pneumonia and severe respiratory illnesses could signal a human pandemic. Our EPIWATCH system looks for early warnings of such activity, which can speed up vaccine development.
If a cluster of human cases occurs, and influenza A is detected, further testing (called subtyping) is essential to ascertain whether it’s a seasonal strain, an avian strain from a spillover event, or a novel pandemic strain.
Early identification can prevent a pandemic. Any delay in identifying an emerging pandemic strain enables the virus to spread widely across international borders.
Australia’s first human case of A/H5N1 occurred in a child who acquired the infection while travelling in India, and was hospitalised with illness in March 2024. At the time, testing revealed Influenza A (which could be seasonal flu or avian flu), but subtyping to identify A/H5N1 was delayed.
This kind of delay can be costly if a human-transmissible A/H5N1 arises and is assumed to be seasonal flu because the test is positive for influenza A. Only about 5% of tests positive for influenza A are subtyped further in Australia and most countries.
In light of the current situation, there should be a low threshold for subtyping influenza A strains in humans. Rapid tests which can distinguish between seasonal and H5 influenza A are emerging, and should form part of governments’ pandemic preparedness.
A higher risk than ever before
The US Centers for Disease Control and Prevention states that the current risk posed by H5N1 to the general public remains low.
But with H5N1 now able to infect pigs, and showing worrying mutations for human adaptation, the level of risk has increased. Given the virus is so widespread in animals and birds, the statistical probability of a pandemic arising is higher than ever before.
The good news is, we are better prepared for an influenza pandemic than other pandemics, because vaccines can be made in the same way as seasonal flu vaccines. As soon as the genome of a pandemic influenza virus is known, the vaccines can be updated to match it.
Partially matched vaccines are already available, and some countries such as Finland are vaccinating high-risk farm workers.
C Raina MacIntyre, Professor of Global Biosecurity, NHMRC L3 Research Fellow, Head, Biosecurity Program, Kirby Institute, UNSW Sydney and Haley Stone, Research Associate, Biosecurity Program, Kirby Institute & CRUISE lab, Computer Science and Engineering, UNSW Sydney
This article is republished from The Conversation under a Creative Commons license. Read the original article.
It was just a few days ago that I said to the wife “sure trump will win the election as soon as pigs can fly”.
I’m so sorry, everyone. I feel guilty
Related article: “If it doesn’t spread from pigs to pigs and it just happened on that one farm, it’s not a big deal,"
Here we go again. It’s fine, just drink some bleach /s
Bird flu? Yeah, they tend to do that?
Yeah another pandemic under Trump let’s gooooo. Surely millions of Americans won’t die when he suggests consuming eagle flu to eat the bird flu
The religious fruitcakes will never get the hint that their god is trying to tell them something.
Yeah, the message is we shrugged off disease, famine, and as much barbarity as we could. We did it, as in humans, all for a better world for our progeny. Its not some mystic divine rite that protects us and drives us, but human minds sharp enough to puncture the veil and approximate the future. The noble mentat reduced to an idol.
I’m concerned for my American friends that have just elected a leader that believes that, and I’m paraphrasing here, “if they stopped testing, they wouldn’t have any cases” as well as hired a guy firmly bent on undermining vaccines and vaccine information.
You’re barely even paraphrasing, that’s almost a direct quote.
Trump: ‘If We Stop Testing, We’d Have Fewer Cases’
Trump: ‘If we didn’t do testing, we’d have no cases’
Trump on coronavirus testing: ‘If we stopped testing right now, we’d have very few cases, if any’
Damn, and here I thought Covid was supposed to make my memory worse.
It’s ok, RFK will fix it.
/s (just in case)
i try to look for silver linings and i think that this and rfk combined makes it possible for another covid like pandemic to take place and maybe that coupled with the dnc’s resurgence could change things around for the country.
experience tells me that this won’t happen because the dnc is incapable of self introspection; but i try to stay positive and always expect change. lol
As things progress, I get more and more afraid. But, I mean, he even wants to remove fluoride from drinking water.
I just hope there is enough adults in the room to keep them in check. It doesn’t seem that way :(
I just hope there is enough adults in the room to keep them in check. It doesn’t seem that way :(
i think that this is the problem that led us into the election results; assigning all the work to an “adult”.
this isn’t an indictment on you; i think that is what most americans do and the “adults” we’ve been trusting became disconnected a long time ago. there were plenty of voices warning us about it, but we went with those “adults” anyways because of tradition; we’re all adults and being one doesn’t mean that you’re right and foresight requires hindsight (eg 2016 election).
and also since we’re all adults things like taxes or voting or fixing our system are our responsibility. only the rich can afford to pay professionals like accountants, lawyers, politicians, etc. to do their “adulting” for them and the dnc’s dependency on doing the same thing means that their version of “adulting” is automatically different than the rest of ours.
No worries, they just elected a guy that said drinking bleach and irradiating people from the inside would be a good idea to deal with viruses and bacteria.
Bird flu? I have the cure. Bear Meat. - RFK Jr. 2025
Rare or medium-rare bear meat only.