Bird Flu in cows and people?

No need to panic, but here's what you should know.

Bird flu, sometimes avian influenza, refers to H5N1 influenza virus, which, you guessed it - typically infects birds.

H5N1, like influenza viruses that infect humans, are considered influenza A viruses.

But “flu” is a catchall for a large group of viruses, the influenza viruses, within the Orthomyxovirus family (which are RNA viruses with a segmented genome). Within influenza viruses, there are different types of viruses: influenza A, B, C, and D.

Influenza types A and B can cause illness in humans (what we collectively refer to as “the flu”). But, there are MANY different types of influenza A and B viruses. There are a total of 198 possible subtypes of influenza A and many subtypes of influenza B.

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Flu A and flu B viruses are classified further based on their surface proteins.

Flu A subtypes are classified by 2 proteins on the outside: hemagglutinin (HA) and neuraminidase (NA): there are 18 HA and 11 NA subtypes (this is where the 198 combinations come from). This is also why we have an annual flu vaccine that includes a few different subtypes, because many different flu viruses are circulating around the world at a given time. For example, this year’s vaccine includes 2 Flu A and 2 Flu B viruses: H1N1, H3N2, B/Austria, and B/Phuket.

Influenza viruses are enveloped viruses with segmented, negative-sense RNA genomes.

The segmented genome bit is important, and its why new flu viruses can emerge so rapidly.

Normally, viruses change over time as a result of accumulated mutations, which can lead to shifts in the virus identity. That’s what’s been happening with SARS-CoV-2 over the last 4 years: whenever you hear about a new variant or strain, it’s a result of this process, called antigenic drift.

But flu viruses ALSO undergo a more dramatic change, called ANTIGENIC SHIFT. Because the genome of flu viruses are segmented, this means when the viruses interact with each other, they can freely exchange pieces and lead to the emergence of a brand new influenza virus. This mixing is how new influenza viruses can emerge quickly.

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What’s going on with this recent bird flu report in cows and people?

When flu viruses that normally infect other species come into contact with each other, they can spread to other species they might not normally infect as often. H5N1 flu is called avian or bird flu, because that type historically infects birds. But it can also infect humans and other animals.

H5N1 flu does not commonly infect humans, but it’s possible. H5N1 is a highly infectious strain of influenza virus known to cause severe (often fatal) respiratory disease in birds. If the H5N1 in question is considered highly pathogenic, it may be referred to as HPAI (high pathogenic avian influenza). In this case, H5N1 mortality among birds, especially domestic poultry, can near 100%.

HPAI virus evolves as a result of wild birds infected with LPAI [low pathogenic avian influenza] interacting with poultry where the viruses mutate to HPAI. Unfortunately, because HPAI outcompetes LPAI even among wild birds, that category of H5N1 is now circulating more broadly, with wild birds also being killed at high rates by H5N1 (this is a topic for a broader ecological discussion in the future).

Unfortunately, spread of HPAI H5N1 is getting more common.

An outbreak in wild birds and poultry was detected in late 2021 and spread across the entire country. In order to try and quell it, farmers needed to cull millions of poultry. Over 80 million birds were killed in 2022, some by H5N1 infection, but mostly by culling to reduce the spread.

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H5N1 can (and does) infect humans, but it is quite rare.

Every year, there are a handful of bird flu cases that occur in humans, usually among farm workers or ornithologists who have been directly exposed to an infected bird. But these cases are pretty rare. While rare, the mortality rate among humans is also quite high, and can near 60%, far higher than typical H1N1 or H3N2 flu viruses that cause our seasonal influenza.

So that’s a concern, in and of itself. However, with prompt medical attention and recognition of symptoms, mortality rates can be improved. Luckily, this recent report of the person in Texas indicates they had mild symptoms (only eye redness) and are isolating and recovering.

What’s new with this recent report is that the human appears to have been infected by an intermediate host, a cow.

This isn’t the first time non-human mammals have been infected with H5N1, but the first documented instance of subsequent transmission to a person.

And it appears to be cropping up in non-bird species, including wild animals, more often, likely as a result of displacing the previously predominant version of LPAI H5N1. Indeed, in 2023 and 2024, reports of infections were noted among goats, sea lions, dairy cows in multiple US states, including in milk samples.

As a note: it is safe to consume dairy and poultry products. Milk is pasteurized, which inactivates pathogens (another reason to get off the raw milk train), and poultry products should always be cooked, which accomplishes the same thing.

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The bigger issue: H5N1 has the potential to cause another pandemic.

Right now, H5N1 can infect humans, but doesn’t do so very readily. However, current genomic surveillance does indicate that H5N1 may be evolving increased transmissibility among non-bird species.

This is obviously a serious concern for global ecology and biodiversity, which I plan to discuss in the future. In addition to that though, it means that humans possible points of exposure may increase.

So if the current H5N1 virus mutates through antigenic drift or even the more gradual antigenic shift, it could lead to a new H5N1 (or an entirely different flu virus) that can not only cause high mortality in humans, but also infect us more more readily. That could be the conditions needed to trigger another global outbreak.

On the flip side, mutations could also lead the virus to become less deadly - remember, mutations are random, so anything can happen as viruses replicate and errors during replication occur.

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So, what should you do?

At the moment, nothing too different from what you’re already doing. This outbreak has been ongoing for several years, and public health and agriculture agencies are already implementing protective measures.

• The US government has a stockpile of H5N1 flu vaccines in case.

• We also have a stockpile of chickens that can lay eggs that we produce flu virus in for vaccine manufacturing (fun fact: the neighboring lab at my graduate school was one of the main labs that developed seed virus for flu vaccine, and our walk-in incubator was always filled with chicken eggs).

• There are some countries that are working on bird-specific vaccines for H5N1, which could limit and slow the spread amongst poultry populations and also prevent unnecessary death of these animals.

A few other details to reduce the possible (but unlikely) risk:

• Avoid direct contact with wild birds and observe them only from a distance

• Avoid touching surfaces that may be contaminated with saliva, mucous or feces from wild or domestic birds

• Avoid unprotected contact with domesticated birds (poultry) that look sick or have died

• Wear protective gear such as gloves and masks if you do need to interact with sick birds (or other animals)

• Practice good hand hygiene after contact with any animal, including chicken and birds

• Hunters who come into contact with potentially infectious birds should always wear gloves when dressing birds and practice good hygiene

• Report any sick birds or unusual bird deaths

  • In the US, the State Department of Agriculture (1-866-536-7593) should be notified immediately if any type of poultry appears infected. Your state may also require reporting any suspected bird influenza cases.

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The vast majority of communicable diseases that cause illness in humans are zoonotic, which means they can be spread from non-human animals to humans. While historically, the proportion was about 60%, in the last decade, zoonotic agents accounted for 75% of human diseases. Influenza viruses are considered zoonotic, and the fact that we are seeing increased spread among other species is a cause for vigilance and concern.

It also raises bigger questions about our interaction with the planet, the global population and land development, and more.

Right now? There is no need to panic, but you should be aware of the complexities of human health, and stay tuned for more information.

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Thanks for joining in the fight for science! 

Thank you for supporting evidence-based science communication. With outbreaks of preventable diseases, refusal of evidence-based medical interventions, propagation of pseudoscience by prominent public “personalities”, it’s needed now more than ever. 

Your local immunologist,

Andrea