Bird Flu Is Raising Red Flags Among Health Officials
H5N1 is a dynamic virus that poses an increasing threat in terms of spillover and pandemic potential.
Daniel Acker/Bloomberg via Getty Images
On January 6, the Louisiana Department of Health announced that a patient hospitalized last month for H5N1 avian influenza had died, becoming the first U.S. death from the virus. To make matters worse, samples taken from the individual suggest that the virus mutated within the patient after infection—meaning it had begun to adapt to infect humans better—raising new questions about H5N1’s pandemic potential.
There have been 66 confirmed human cases in the U.S., the majority of which have resulted from exposure while working on poultry or dairy farms. Most cases are mild, and the risk to the general public currently remains low, but the escalation of high mortality in other mammals is another red flag for public health experts.
In this Q&A, adapted from the January 14 episode of Public Health On Call, Stephanie Desmon speaks with Meghan Davis, DVM, PhD ’12, MPH ’08, associate professor in Environmental Health and Engineering, and Andrew Pekosz, PhD, professor in Molecular Microbiology and Immunology, about why it’s time to double down on efforts to limit H5N1 transmission among cattle and birds, concerns about cats and other mammals, and how to prevent the virus from gaining a foothold in humans.
Last week, there was a death from the bird flu. Where do things stand today?
Andy Pekosz: We're seeing signs that this virus is really moving into humans. There was an infection in a person in Louisiana, who apparently acquired the infection because he had a backyard flock of chickens that had become exposed to wild birds. The chickens the person was raising, as well as the wild birds, were found dead. The person who was exposed to H5N1 was hospitalized, and died from the infection.
If that wasn't serious enough, when the CDC scientists sequenced samples from this individual, they found that the virus had started to mutate at two particular sites that we know are important for H5N1 to adapt to better replicate in humans. This mirrors a case that happened about two months ago in British Columbia. We need to double down our efforts to make sure we limit H5N1 infections in humans, to try to lower the opportunity for this virus to learn how to infect humans effectively.
Does flu season complicate the situation?
AP: On the positive side, a lot of hospitals and areas are now testing extensively for influenza. That increases our monitoring, because if we find influenza-positive cases, we can determine whether they're seasonal flu or H5N1. In that way, our testing is becoming more robust.
The concern is that in a person who is infected with both seasonal influenza and H5N1, those viruses may exchange genetic material and make a virus that's better able to infect humans. That's called reassortment. It’s a very rare event, but we know that reassortment has resulted in the influenza viruses that have caused the last three human pandemics.
Are we at a dangerous point with this virus?
Meghan Davis: We are if you're a house cat. When this virus infects cats, it causes extremely severe disease and very high mortality rates.
We've had a number of product recalls linked to H5N1 cases, not just of contaminated raw milk, but also raw meat pet food products. If people are exposed to the virus through their pets, it may be a different kind of exposure than what we've seen before. In individuals who are immunocompromised, that could mean either different kinds of mutations in the virus or a different clinical manifestation of disease.
We still have a very large outbreak in cattle.
MD: Yes, although California, which is the leading dairy state and the epicenter of what we're seeing currently, is starting to get a handle on it. We've seen a decrease in the new herds identified. But we're still at over 300 herds nationally.
AP: It's important to note that those two serious human influenza infections—the one in British Columbia and the one in Louisiana—are H5N1 viruses, but they're a slightly different form of the virus than is infecting dairy cows.
H5N1 is a very dynamic virus. There's lots of versions of it circulating in lots of different animals and birds, and it's continuing to pose a greater and greater threat in terms of spillover and leading to a pandemic.
Should we be concerned about person-to-person transmission?
AP: Absolutely. The mutations that have been detected in infected people probably alone won't allow the virus to transmit. We have no evidence of transmission yet, but we need to do more surveillance in broader populations that are at risk. We know that the virus can cause mild disease in certain situations, but that means we probably need to test more extensively to figure out how much of that mild disease is being caused in these spillovers into humans.
MD: If we start to see sustained human-to-human transmission, that is a huge red flag and cause for concern beyond the normal “threat level: high” for public health professionals. That would mean that the public, outside of these high-risk groups, would need to be more concerned.
It's also important to mention that we have seen sustained animal-to-animal transmission, and not just in birds, but also in mammals, and not just dairy cows. There have been studies that have shown ferrets can transmit to other ferrets, and this is another species that is particularly susceptible to influenza viruses. This gives the virus more opportunities to “fine tune” if there is a mutation—to select for strains that could be more adapted to mammalian transmission.
What can we do going forward to avoid a pandemic?
MD: We should certainly be doing more animal surveillance, and we are starting to. For dairy cows, there's a way to test en masse, using bulk milk tank tests. This means that you're checking the pooled milk from hundreds of cows for H5N1. If you get a positive test, you can go back to the original farm to identify which cows may be infected. This is absolutely essential for controlling spread from dairy cow to dairy cow, whether through direct cow movement, personnel, equipment, or another mechanism.
We suspect, because we see a lot of farms in proximity to each other getting it, that there could be roles for other animals in the transmission. While this makes sense for wild birds, we need to do more surveillance on creatures like field mice, some of which were confirmed to be infected in Colorado. Understanding that disease ecology is essential.
Looking at other species would also be very important. We know that goats are susceptible, so small ruminants could be the next area where we increase our surveillance. The more we know about where the virus is in animals, the more we're able to not only halt the spread within at least the species that we raise for food, but also know which people may be at greatest risk of exposure.
Is the general public at risk?
AP: We know that the infected cases that we've documented have come from exposure from working on a dairy farm or at a poultry facility, or exposure to backyard flocks of birds or wild birds that are infected. Though we haven't had a confirmed human case of H5N1 from raw milk, we've had plenty of examples of animals getting infected by it. If you're in one of those areas, you should practice more caution, or in the case of raw milk, just don't consume it.
Should people handling poultry wear a mask or thoroughly wash their hands to avoid infection?
MD: You should take a lot of care if you have any encounters with livestock. There is a possibility for birds early on in infection to not have as many symptoms, and there are a lot of things you can get from poultry, so I always recommend using excellent hygiene when coming into contact with them.
Checking what's happening in your area by going to the USDA website may also help you make some decisions based on the current risk in your area. Right now is when people [who are exposed to poultry] should be on high alert and change what they do if it's in the area.
If you keep backyard poultry, there are resources available. The USDA and many land grant universities with extension services have a lot of materials on what you can do to protect your birds and your own health when working with them.
What factors would indicate to you that this is becoming a greater threat to humans?
AP: The critical thing is understanding whether the virus that's in dairy cows right now will pick up mutations that will help it to be more transmissible in mammals. We know that mammary milking equipment is transmitting the virus from animal to animal. If the virus changes the way it transmits and becomes a respiratory pathogen among dairy cows, that would be another sign that this virus is changing and posing more of a risk to the human population.
What is the impact of all of this on the dairy industry?
MD: Honestly, this is an existential crisis. There's a lot of cost that goes into raising and keeping animals. We don't yet know what the hit is going to be in terms of long-term health for animals that were infected. We know they can survive, but many of them could have impacts to their productivity for years, perhaps the rest of the animal's life.
In addition, the dairy industry has not had to address this kind of biosecurity need in a very long time. Most of the barns—which are expensive to build—in warmer climates are dry lot dairies, meaning that they've got a roof and no sides, which allows birds, cats, mice, and other things to come in. Reengineering these farms could take a very long time. You have 25,000 or more decision-makers among the dairy production industry, and there are so many different ways of raising dairy cows, that there's not going to be a one-size-fits-all solution.
This interview was edited for length and clarity by Morgan Coulson, an editorial associate in the Office of External Affairs at the Johns Hopkins Bloomberg School of Public Health.
