All about bird flu / avian influenza with Dr. Maurice Pitesky

Last Updated on February 18, 2025 by Susan von Frank

Bird flu, aka avian influenza… What is it? If you raise backyard ducks and other poultry, how does bird flu effect you? Where did these viruses come from, how are they changing right now, and what should we expect moving forward? If you raise poultry, how can you reduce risks to your family and your flock? 

We reached out to one of the country’s top avian influenza experts, Dr. Maurice Pitesky, to get the latest, most accurate information to help you better understand avian flu, its risks, and protective steps you might consider.  

Who is Maurice Pitesky?

Maurice Pitesky runs the Pitesky lab at UC Davis School of Veterinary Medicine-Cooperative Extension (UCCE). He is a faculty member at the UC Davis School of Veterinary Medicine-Cooperative Extension (UCCE) with an appointment in poultry health and food safety epidemiology. Dr. Pitesky’s research interests are focused in three major areas:

1. GIS based mapping/modeling to understand how avian diseases move in time and space;
2. Novel data analysis and visualization tools to gain insights into poultry production and food safety; and
3. Gaining a better understanding of non-conventional commercial poultry production.

Avian flu Q & A with Dr. Maurice Pitesky, D.V.M., MPVM, Dipl., ACVPM

This interview originally took place via a Zoom call. The written Q & A (below) has been lightly edited for brevity and clarity.  

Question 1. The terms “bird flu” and “avian flu” are rather broad… My understanding is there are two distinct bird flu species currently infecting animals (including domestic ducks) throughout North America: H5N9 and H5N1, along with subvariants of H5N1 such as B3.13 and D1.1. Is that correct or can you elaborate if not?

That kind of captures it. At the broadest level, we talk about avian influenza / bird flu. And we’re in this version, especially the H5N1, B and D genotypes specifically, which seems to be popping up in all kinds of different species: wild birds, domestic birds, wild mammals, domestic mammals, humans – for the D genotype. Because the virus is an RNA virus, and because it’s segmented, it’s just in little pieces, kind of like our cells have 23 pairs of chromosomes.

The avian influenza virus has eight segments, if I can remember correctly. (I’m not a molecular person.) Long story short, when they sequence the virus, they can get new insights on how the virus is mutating and reassorting.

But in a general kind of sense, we still put it under that umbrella of “avian influenza,” even though we have avian influenzas that infect mammals and other species now. For example, the B and D genotypes have been found in dairy cows.

In California, where we have a huge dairy state, we primarily find the B genotype. In Nevada, we just had a very interesting case of wild birds transmitting the D genotype to dairy cattle. And that also got a farm worker pretty sick with what was basically a version of pink eye plus some flu-like symptoms.

Not to go into too much detail here, but the fascinating thing that’s going on in dairy cattle here in California, is that with the main B genotype, when the cows get sick, they lose production, don’t move around as much, and don’t eat as much.

However, in Nevada, with the D genotype, the cows didn’t show any clinical signs at all. And it’s almost like a “Trojan horse” because a worker got sick. And the only reason we found the D genotype is because they found it through testing of the bulk milk. 

So that’s a little scary from a public health perspective. And also, the “nice” part about when animals get sick, when they get infectious diseases, is that it gives the farmers and first responders in the state and federal departments of agriculture kind of like a heads up that we’re probably dealing with some type of disease, possibly an influenza.

Question 2. Can you briefly describe the history of these viruses? For instance, how long have they been around, which came first, how closely are they related, etc?

Most folks, when trying to describe the history of these viruses, go back to 1996 in Southeast Asia and China.

There was a case where an influenza virus moved from wild birds to domestic poultry, I don’t know if they were ducks or chickens. And then the virus kind of mutated and the version that came out is this kind of H5N1 highly pathogenic avian influenza.

And then that virus went back to wild birds. That happens because of the spatial interface between domestic agriculture and wild birds, which is kind of a method of disease transmission that we need to keep a very close eye on.

From there, it’s spread on and off throughout the world, primarily through wild waterfowl. Historically, ducks and geese didn’t seem to show any infectious signs. So when we had highly pathogenic avian influenza, H5N1, I believe it was in 2014, 2015 in North America, we didn’t have the die offs of wild birds that we’re seeing right now. What we’re seeing now is extraordinary and very unique at multiple levels.

First of all, we’ve got this virus on six continents. And then, like I mentioned, it’s kind of ubiquitous in wild and domestic birds and wild and domestic mammals and also in the environment. We’re finding it in wetlands, lagoons, human wastewater… So it’s kind of been shed all over the environment and the amount of species that are positive for it is extraordinary. 

But to answer your question, most people go back to that 1996 event. I think if you went before that, you would still find influenza viruses floating around. But this specific H5N1 seems to start around that period of time as far as domestic culture.

Question 3. What do you think is the primary mode of transmission for these viruses: feces, saliva, something else?

If you look at ducks and geese, which are still the primary reservoir for avian influenza, they can shed the virus in their feces or their respiratory effluent.

So that can be spread as ducks and geese go on their evening feeding flights. That can spread the virus through aerosol routes.

In California, for example, we’ve lost 95% of our natural wetlands. So because of that we have more wild birds, including waterfowl, that are congregating on less and less habitat. So it’s been speculated that we’re getting increased transmission because there’s more densely concentrated waterfowl and other species.

And you guys [on the east coast] have some of the same problems. You know, it’s interesting because people want to know what we’ve done accidentally to create this situation.  

Obviously, I think there’s a role that climate change has played in this. But I think the bigger role is the human-built environment, and how we haven’t always thought (to put it politely) where we put our farms relative to habitat for wild birds.

For instance, in the Central Valley of California, we have a thousand dairies or so, we have about 600 poultry facilities, and during the winter we have over 6 to 8 million wild waterfowl. And since we have vastly reduced natural wetlands, then the birds use what I call suboptimal habitat.

And a lot of that suboptimal habitat is very close to a lot of these farming facilities where we produce our milk and meat. 

Question 4. My understanding is that the risk profile of avian influenza infection varies by animal species. For instance, with H5N1 many mammals and bird species are highly symptomatic when infected with H5N1 and also have very high mortality rates (chickens being a good example). However, wild Mallard and Mallard-derived domestic ducks have typically been considered “trojan horses” when it comes to H5N1; that’s to say, they might carry and spread the virus, but they’re typically asymptomatic and very rarely die from infection.

• Is this assessment correct?
• If so, what accounts for the risk profile differences between host species?
• With ducks, do the same risk profile generalizations for H5N1 hold true with its subvariants and/or with H5N9?

The short answer, at least from my knowledge, is we don’t know. So, when you look at, for example, why are layer flocks more affected than broiler flocks? Why are turkeys more affected than broilers? There might be some species variability there, but I don’t think we know enough to really say for certain.

So I think some of it is geographical in the sense that most of our turkeys and layers are in areas where there just happens to be a lot of wild waterfowl habitat. But we do have broilers that have gotten sick and ducks obviously that have gotten sick also.

Some people talk about different breeds and species that might have some resistance, but I think from a practical perspective, I’m not sure what the value of that even is. They’re still susceptible and they still get infected and they still get disease. I know in California we’ve definitely had ducks that have been susceptible.

Question 5. At present, which bird flu species or variant seems to represent the biggest health threat to ducks? To people?

For people, the answer is definitely the D genotype [of H5N1].  The person who died in Louisiana, who was over 65 years old, I think that person was a backyard poultry enthusiast and got the D genotype that way. There’s been several other folks, including a teenager who has been in an ICU in British Columbia for a while that also contracted the D genotype.

The dairy worker in Nevada got sickened with the B genotype. The B genotype is the one that we find on dairies, and we’ve had several dairy workers exposed to that one. So on the human side, there’s a risk with both genotypes, although I think there’s probably evidence that D is a little more severe than B at this point.

But these viruses are extremely volatile as far as their genetics, so they can continue to reassort. And one of the worst case scenarios we really worry about is in humans. You know, you have dairy workers, for example, who aren’t vaccinated. And you’ve got human influenzas in some cells mixing with some of these avian influenzas. And you worry about a scenario where you can get a reassortment that would cause a highly virulent, highly pathogenic strain to come out.

Now, on the duck side, you’re asking about the B versus the D genotype and the H5N1 or the H5N9, because there was that duck farm in California that had both H5N1 and H5N9. I don’t know enough about it to truly comment on it, but in a generic sense, we don’t know what the significance of the virus [H5N9] is with respect to pathogenicity, infectivity, if it’s as ubiquitous as far as the different species that it can infect… 

I will point out that when you look at the types of variants that are floating around in wild birds, it’s not just one variant. There are a lot of different types of avian influenza. There was a paper that came out maybe six months ago that showed that the dominant strain was this D genotype, but that there are other strains that are floating around in wild birds.

As far as which variants are going to persist and which ones are going to evolve: a lot of that happens in the summer in the Arctic when all the birds head back north again and they interface there. 

For example, I’m from California, so the Pacific Flyway interfaces with the East Asian Flyway up in the Arctic. So we don’t have a really robust surveillance system up there. But come summer and fall, we can kind of start not only looking for virus from cloacal and oropharyngeal swabs from the birds, but you can also start sampling the ducklings and goslings to see what percentage of them are carrying virus, because that’s really important to understand, you know, the transmission dynamics.

A couple years ago, there was a study done by a colleague of mine that showed about 40% of the ducklings and goslings were carrying H5N1, which is obviously evidence to suggest that the virus continues to cycle from adults to babies.

One thing that kind of strikes me too, as I’m talking to you about these species going back and forth around the globe, is the importance of having a global collaborate effort to better monitor, track, and understand these viruses because they are not bound by borders. 

If you go on the USDA’s website or Canadian Food Inspection Agency’s website, I always get a little frustrated where the surveillance stops at the border. I know a lot of these people, and they’re all good scientists, but I’m like, “my God, what if I have a turkey farm or layer farm in Minnesota or Iowa. I kind of want to know what’s going on up north before fall migration.” It’s not an easy process to see what viruses have been detected, and when and where they’ve been detected.

And this goes to the issue of: we currently don’t have very good information networks. We have a lot of siloed data. We collect a lot of good data, but the way that it’s networked is much harder.

Question 6. Assuming this terminology is correct because I am not a scientist, but has there been any indication of hybridizing, horizontal gene transfer events happening between H5N1 and H5N9 yet? Is that outcome likely — or even an inevitability with enough time?

I don’t think so, but I’m not the gene jockey. But I would say it’s kind of playing a game of probability, so that the more virus that’s present in different species and in different environments, the more potential for reassortments. 

When you get a reassortment, you get a significant shift in the genetics of the virus. And that’s scary because now you have the potential for not only something virulent and infectious, but something that we’re immunologically naive to. That’s a problem. So the more virus you have floating around, the greater the risk. 

And this kind of goes to the concept of vaccination. So I’m not an expert in vaccines, but I keep telling anyone that’ll listen, “okay, if we’re going to go down the road to vaccination like they do in Egypt and most countries in Asia, we need to have a really robust surveillance tool.”

Because from a practical perspective, the vaccine will only work if we’re doing surveillance and making sure that the dominant versions of the virus that are in wild birds, which are ostensibly then going to be in commercial poultry and cattle, among others, that we’re matching them, or else we’re just vaccinating blindly.

The other problem is that when you vaccinate, you do kind of put your thumb on the scale of evolution. There was a paper that recently came out suggesting that vaccinated flocks seem to have higher mutation rates in the hemi glutenin protein, that’s the H part of the H5N1. And that’s a little scary from a public health perspective and probably a veterinary health perspective.

However, the way the study was set up, it wasn’t causal. So we don’t really understand why. But it was definitely an interesting observation.

Like I said, I’m not against vaccination. I don’t know enough about it, but my guess is we’ll probably have to do it. We have a lot of chickens in the US, so the idea that we’re just going to vaccinate everything is probably a little simplistic. So we probably need to target it and we probably need to align our vaccination if we’re going to ramp up for vaccinating animals.

There’s a lot of controversy about this that I’ll defer to others on. But if we’re going to do that, we need to put a robust surveillance system in place. And unfortunately, every time I see someone saying we need to vaccinate, they never — even though they’re scientists — talk about having a robust surveillance system of wild birds in place first.

Hey, we’re humans, so sometimes we can only do one thing at a time. But I’m afraid we’re going to start vaccinating, and then we’re going to be like, “Oh, shoot. Now we need to put a surveillance system in place.” And that’s not the order we should go in. 

Question 7. Assuming that a farm animal is infected, is there a high risk of avian flu infection for people who do the following:

• drink raw milk?
• eat under-cooked meat?
• consume raw eggs? (Now I’m thinking about people who eat beef tartare – ha.)
• eat cooked eggs?

Raw milk – So my answer to that would be yes. Even though if there was a raw milk dairy producer here, they might say, “well, show me an example of someone who drank raw milk and got sick.”

To which I would say two things. One, a lot of feral cats have died on dairy farms, ostensibly because of raw milk consumption. And two, we are seeing farm workers that are getting pretty severe infections in their eyes, like a pink eye infection.

If cats are dying and we know the virus is infectious in humans, as someone that studies epidemiology and knows that outbreaks are easier to stop before they happen, I would say you are playing with fire with that knowledge and then telling me that we could still sell raw milk to people. 

So I would say that’s the context in which we should not be selling or consuming raw milk.

Undercooked meat – We’ve also had some situations where turkeys had virus in their meat. Their meat was sold under some commercial brand, and for some people, it’s a thing to feed their cats raw turkey. Then their cats got avian influenza. So yes, it’s a risk factor.

Cats have more similarities than differences with other mammals. Plus they live in a situation where they’re co-housed with humans in a lot of situations. So in my mind, why would we do that?  

Raw eggs – In general, laying hens stop producing eggs when they get the virus. They stop producing eggs and they die. So in a broad sense, we don’t have to worry too much about any eggs being produced by infected hens.

But there could be a scenario where an egg had some feces on it, so there’s virus on the shell. And it was in a backyard flock, so they didn’t wash the eggs (which they should do with backyard eggs in my opinion). So that could be a risk. 

We do have some research suggesting the virus can be present in a raw egg, but that’s not the tissue that the virus really focuses on.

The CDC says that one out of every 10,000 eggs has Salmonella Enteritidis on it. So steak tartar is a risk for that. But I would say for avian influenza, it’s an even lower risk because it’s just not a tissue that the virus seems to co-locate in for the most part. 

Question 8. Does high heat (e.g. cooking food) kill both H5N9 and H5N1? Any important details as to what temperature and duration is required?

Yeah, they’re actually pretty wimpy viruses. So as long as you pasteurize milk, it eliminates the risk. If the virus is detected in milk, in theory, they’re supposed to pasteurize and dump it.

What was happening is there was raw milk that was infected that was being dumped in dairy lagoons. Then wild birds would go into those lagoons. And that wasn’t happening because dairy farmers are stupid or lazy. It’s just that pasteurization is expensive and you’re not going to be able to make money. I’m not a regulatory person, but I think dairy farmers should get indemnified, like poultry farmers do, for lost milk sales.

But you have to give something to get something. And they [dairy farmers] should be required, among other things, to participate in a more robust fashion in human public health surveillance and in biosecurity audits.

Question 9. What should a person do if they find a dead bird or animal in their yard? Leave it alone? Put on an N-95 mask and nitrile gloves and dispose of the animal inside a plastic bag? If you have foraging backyard ducks or chickens, does the answer to this question change?

Yeah, great question. So I would contact your state department of Animal Health, state Department of Agriculture and see if they want to collect it for surveillance purposes.

Until you hear back, then at a minimum, you should probably put on a surgical mask and some gloves, and put the bird in a plastic bag. And if you don’t hear back from anyone, just double bag it, tie it off, and put it in the trash, because what you don’t want to happen is further transmission of any disease to any wild or domestic animals in your immediate region.

Question 10. Any tips for reducing the risk of infection from wild animals to backyard ducks / poultry? A few things we thought of (and please correct any that are off-base):

1. Don’t put out wild bird feeders near your flock.
2. Don’t put out artificial bird houses near your flock.
3. Possible: Don’t keep food out all day. Instead, only feed small amounts of food at set times so all the food is eaten immediately (to reduce risk of other animals like squirrels and wild birds contaminating the food).
4. Possible: Keep ducks inside a covered run during the day rather than allowing them to free-range in areas where wild bird or animal feces may be present.

Those are all good, but a few comments on #3. I would say the nuance there is you can feed them, but just make sure, for example, at night that there’s no spilled feed, and you put away any feed or water. And that’s why I like pelleted feed instead of crumble feed, because pelleted feed is just a little easier to clean up.

And then the only other thing, and you know more about ducks than I do, but I guess I’m wondering how you keep rodents and wild birds out of the litter, water, and food in there. So question for you: is there a way to do that that you think would be helpful or not really?

Aaron response: Yeah. We have a rodent-proof duck coop. So there’s no way rodents can burrow in. When the ducks are in there at night, nothing can get to them. So even if they make a mess, nothing else other than a duck is going to access it. And then during the day when we let them out, we can just close up and lock our coop, so nothing can access it by day either. When we’ve left the coop open in the past, we have seen wild birds and squirrels in the duck coop during the day looking for food.  

Question 11. What should a backyard poultry keeper do if they notice their birds becoming sick?

You know, before you buy birds, you should have a veterinarian that you have a good relationship with so you can chat with them. But that’s important at the beginning to have that person identified. A veterinarian who can give you some guidance on how to proceed.  

Because who knows what you’re dealing with? It might be something completely unrelated.

Question 12. Any tips for reducing the risk of infection from backyard ducks / poultry to their human caregivers? Should people be taking precautions like masking and wearing gloves around their poultry – especially if they’re immunocompromised?

Yeah. Now, in addition to boots and overalls, I recommend people wear surgical masks just to give them some protection because there’s a lot of aerosols generated and the virus is so ubiquitous in the environment. 

I’m trying to like thread this needle in the sense that I know people don’t like wearing N95s. And to me, a surgical mask offers some protection. I think with kids, gloves are a really good idea because they have a tendency to go to their face and eyes with their hands.

Aaron: Our son knows never to touch his face when he’s helping us with the ducks. Shoes stay outside and never come indoors. And the first thing we do when we get back inside after duck duties is wash our hands with warm, soapy water. 

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We’d like to thank Dr. Pitesky of UC Davis School of Veterinary Medicine-Cooperative Extension (UCCE) for taking the time to share so much useful information about avian flu! If you’re a backyard poultry keeper, we hope you find this information actionable and helpful. 

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Or check out the latest duck articles from Tyrant Farms!