Resurgence of bird flu sounding alarms
More mammals are getting infected; risk for humans low
When Dr. Jonathan Runstadler was called to the scene at Nahant Beach in March, he found more than 70 dead birds littering the shoreline, including sea ducks, loons, and sea gulls.
State officials had called Runstadler, a virologist, to the North Shore to test the dead animals for bird flu, which has been devastating wild flocks in New England since early 2022. Within a few days, Runstadler, of the Cummings School of Veterinary Medicine at Tufts University, confirmed that the birds were the latest victims of a highly pathogenic strain of H5N1, a bird virus that resurged in Massachusetts in January after waxing and waning over the previous two years.
This potent version of H5N1 has killed millions of birds in the wild and on commercial poultry farms around the world since it first emerged in Europe in 2020. But of greater concern to scientists is this strain’s ability to infect mammals. In the summer of 2022, it killed more than 180 gray and harbor seals off the coast of Maine. Last year, tens of thousands of seals and sea lions off the coast of South America fell victim. Last month, a sick goat in Minnesota became the first livestock animal in the United States to contract H5N1, and within the last two weeks, the US Department of Agriculture announced that cows had been infected for the first time on farms in Texas, Kansas, New Mexico, Idaho, and Michigan.
“The globe is just being slammed by this virus,” said Wendy Puryear, also a virologist at Tufts.
Most of the mammals infected with H5N1 over the last several years are believed to have contracted it directly from wild birds rather than from each other. But on Monday, state and federal officials reported a person in Texas was being treated for bird flu after having direct exposure to dairy cattle presumed to also be infected. If proven true, it could be a very rare case of
mammal-to-mammal transmission of the virus.
“It seems to be infecting all sorts of animals that we didn’t previously see it infecting,” said Jennifer Nuzzo, a professor of epidemiology and director of the Pandemic Center at Brown University School of Public Health, who called the development “alarming.”
Scientists worry that as this highly pathogenic strain of H5N1 continues to move around the globe, it could evolve mutations that make it spread more easily between mammals, including humans.
“It’s one of those things we’re watching very closely,” Puryear said.
While previous versions of bird flu have proved fatal to humans, the person infected in Texas reported eye redness and inflammation as their only symptom and is recovering. According to the Centers for Disease Control, several vaccine candidates for bird flu are already in development and could be manufactured if necessary.
Puryear and Runstadler were part of the team that discovered bird flu in the gray and harbor seals off the coast of Maine. The virus has not been recorded in New England seals since then, but Runstadler suggested that could change “any day” as the disease continues to spread in coastal birds.
Most of the infected birds in Massachusetts live along the coastline, according to Andrew Vitz, MassWildlife’s state ornithologist. Data provided by the Department of Agriculture show an uptick in the state’s cases starting in mid-January, particularly in Canada geese.
In addition to the dead birds in Nahant Beach, Puryear said sick flocks have recently been reported in other parts of the North Shore, including Salisbury, Newbury, Plum Island, and Manchester-by-the-Sea.
Vitz said infections are currently at a similar level to this time last year, which then petered out during the summer. That’s different from summer 2022, when the number of dead birds ramped up throughout the spring and exploded in July.
“That surprised everybody in 2022, when it stuck around through the summer,” Vitz said.
Scientists are still trying to determine what has caused the recent increase in bird flu cases in Massachusetts. According to Puryear, spring migration patterns and the introduction of new H5N1 lineages to the region may be contributing.
It’s also uncertain whether cases will go down in April as they did last year or continue to spread, like they did in the summer of 2022.
“If I have learned anything about highly pathogenic influenza in the last year, it’s that we cannot predict or anticipate anything,” Puryear said. “It has just ripped up all the rule books and thrown them out the window.”
Even if the virus fades in the summer, Vitz said, he expects it to reemerge later on. Runstadler and Puryear agreed that the virus seems like it is here to stay.
The CDC had previously reported just one H5N1 case in humans in the United States since 2022, but the agency said people who regularly interact with commercial poultry should be careful when handling sick or dead birds. The new case reported Monday does not change the risk for the general public, which remains low, officials said.
The Massachusetts Department of Agricultural Resources has also advised backyard flock owners to take precautions to minimize contact between their chickens and wild birds.
Investigators are still trying to better understand whether transmission has occurred among marine mammals in South America. On Friday, the Department of Agriculture said the emergence of the virus within herds of cows indicated that “transmission between cattle cannot be ruled out.” Bird flu symptoms in cattle include decreased lactation and low appetite, according to the USDA.
Nichola Hill, a disease ecologist at the University of Massachusetts Boston, said the public plays an important role in identifying and reporting sick flocks. But she and other scientists advise people not to touch or interact with sick or dead birds. They said pet owners should be wary.
“It’s really not the time to let your dog off-leash on a beach and get a seabird between its jaws that may or may not be infected,” Hill said.
On Monday, the CDC said that existing bird flu vaccine candidates for humans could be manufactured quickly and that preliminary testing showed they could provide “reasonable protection” against H5N1 viruses.
“This is not like we’re starting from ground zero,” said Syra Madad, an infectious disease epidemiologist at NYC Health + Hospitals. “We’ve known about this [virus] for many, many years, and we luckily have effective therapeutics and candidate vaccines that can certainly be scaled up. From that standpoint, we’re at an advantage.”