BU infectious diseases expert says scientists are watching closely
News reports of chickens and wild birds dying off. Culling of commercial flocks to prevent further spread. Sharp increases in egg prices. At the moment, these are the main effects of a major global outbreak of the H5N1 strain of avian influenza—bird flu.
According to the Centers for Disease Control and Prevention (CDC), the risk to the public is low. But governments and scientists around the world are watching closely for any changes that could portend a new pandemic.
So far there has been little to no human-to-human transmission of bird flu, says David Hamer, a Chobanian & Avedisian School of Medicine professor of medicine and a School of Public Health professor of public health.
The virus would have to mutate to spread widely among people, says Hamer, who is also interim director of BU’s Center for Emerging Infectious Diseases Policy & Research (CEID).
There have been a small number of human cases in the last year, primarily in Asia and apparently caused by close contact with poultry. But the virus has already jumped to other mammals, including mink and foxes. And if human-to-human transmission does become a reality, the mortality rate could be high, says Hamer. Previous pandemics, such as the 1918 flu pandemic that killed about 40 million people, originated in birds.
However, humans have gotten better at facing down pandemics in recent years, from field surveillance identifying outbreaks to the creation of vaccines, says Hamer. In part that’s a side effect of the coronavirus pandemic.
Hamer serves as interim director of CEID until April 1, when director Nahid Bhadelia returns from a sabbatical serving as senior policy advisor for the White House COVID-19 Response Team.
We talked to Hamer about the threat from H5N1, how the disease is different from other strains of flu, and why a human H5N1 pandemic is something we very much want to avoid.
with David Hamer
BU Today: Let me start with a personal question. My wife volunteers at a local historic farm. One of her duties is tending to the chickens in the coop, and she brings home eggs. How concerned should we be? What precautions should we take?
Hamer: Avian influenza has reached some domestic poultry populations, but it’s much more commonly being found in wild bird populations. So I think the risk is still relatively low. I think if there were an outbreak, they would be able to recognize it, because they’d have sick chickens. But good hand hygiene is important. And then, if she wanted to be really cautious, wearing a mask while she’s handling the chickens would be a reasonable thing to do.
BU Today: We can’t get it from eating eggs?
Hamer: It’s spread by droplets, respiratory aerosols, but also apparently through close contact with infected birds. And so if you get it on your hands and rub your nose, eyes or mouth, you could become infected.
BU Today: The poultry industry is culling millions of sick birds worldwide, but the disease has also hit wild bird populations very hard?
Hamer: Wild outbreaks were confirmed in 47 US states, according to a Pan American Health Organization (PAHO) alert, so it is very widespread. We find it in ducks, gulls, pelicans, swans, vultures. It’s been found in just about all sorts of different species of wild birds.
BU Today: This is not a new disease?
Hamer: It’s been around for a couple decades; we’ve been watching sporadic cases. Most of the human cases have been in Southeast Asia, and with a couple of exceptions almost all of those are single episodes, or maybe a family at most, that often had home poultry operations, a lot of close contact with sick chickens, and then became infected. But the notable thing is that it hasn’t generated additional personal-to-person spread.
BU Today: It’s said there have been at least 14 human cases reported in recent months, 11 of them fatal. That’s bad, right?
Hamer: Our worry is that if it mutates, and becomes more able to spread person-to-person, we’re in trouble, because if you look at the sort of average fatality rate of avian influenza, it’s pretty high. One study suggests that it is 14 to 33 percent for H5N1 but they note the World Health Organization estimates up to 60 percent. This compares to 0.1 percent or less for the strains of influenza that cause annual seasonal outbreaks in humans.
BU Today: Could this just fade away?
I think it’s here to stay because of its widespread presence in wild bird and wild mammal populations.
BU Today: How is H5N1 different from other strains of bird flu?
The H and N stand for hemagglutinin and neuraminidase, two proteins that are involved in attachment of the influenza virus to human respiratory mucosa and its release into the respiratory tract. There are important differences between strains. H5N1 can attack the lower respiratory tract, which leads to a severe, life-threatening form of pneumonia, but it’s somewhat less able to bind in the upper respiratory tract and lead to lots of secretions that lead to transmission.
BU Today: How does the 2009 H1N1 pandemic compare to this new threat?
Influenza viruses can basically recombine between pigs, birds, and humans. The 2009 flu was a sort of recombination between pig and human elements, and it was so different that our immune systems didn’t recognize it. And that led to pretty much a global pandemic. That was interesting because a lot of the cases occurred in the spring and summer, which is not the typical time of year for influenza.
BU Today: But it needs to mutate before we really have to worry?
What I’m worried about is this: If there’s an interaction between pigs and domestic poultry, and there’s some sort of recombination between a swine influenza and an avian influenza that has the right characteristics to infect humans and be transmitted person-to-person, then we could have a pandemic.
BU Today: Given what happened with COVID-19, how prepared are we?
There is some vaccine development. We have treatments. We have antiviral drugs for influenza A and B, the main types of the virus that cause human infections. The neuraminidase inhibitors, the main category of drugs we use, should work against avian influenza, but we may need to be ready with additional new treatments that work if there’s an outbreak, as well as vaccines.
I also think we have better surveillance systems in place than we did 20 years ago, or even a decade ago. There’s a lot more attention being paid to identifying novel viruses, and I think COVID has helped accelerate that process. But we definitely need to be on our guard. Of new diseases, most are zoonotic—they’re coming from animals. And so we really need to be monitoring animal populations anywhere there’s a greater interface between humans and animals. That’s backyard poultry operations and people in the rainforest where they’re cutting down the forest and having close contact with wild animals, both examples of settings where animal-to-human spillover events may occur.