Massachusetts’ bird flu outbreak is the largest in the state to date, local environmental and public health officials announced Wednesday.
They said 500 to 1,000 wild bird deaths, suspected to be from avian flu, had been reported around Massachusetts, though the actual number is likely higher.
Still, they said, the risk to humans is extremely low, and the biggest risk of infection remains through close, prolonged contact with a sick animal. Most human cases are mild, though one person in Louisiana died from the flu earlier this month. The person was older than 65, had underlying medical problems, and had been in contact with sick and dead birds in a backyard flock.
“We feel like awareness is the right approach as opposed to alarm,” said Catherine Brown, the state’s epidemiologist, in a press briefing. “While the current H5N1 avian flu has had significant impacts on dairy cattle, domestic birds, and wild birds in the US, avian flu viruses very rarely infect humans.”
The rise of bird flu in Massachusetts and nationwide comes at an uneasy time for public health, as the new Trump administration, hours after taking office last week, froze many federal health agency communications with the public through the end of the month. The halt has meant that data collected by infectious disease workers on bird flu, and many other health risks at the state level, have not been shared with, analyzed, or widely disseminated by the federal government agencies charged with monitoring such outbreaks.
Public health experts said the unprecedented pause has created a troubling blind spot.
Howard Koh, a professor at the Harvard T. H. Chan School of Public Health, said he’s alarmed by the Trump administration’s temporary gag order at a time when the trajectory of the bird flu threat is accelerating.
“A communications freeze is not what we need right now,” said Koh, a former Massachusetts public health commissioner and US assistant health secretary during the Obama administration. “That’s very serious. When communications should be paramount, instead it’s been silenced.”
Koh said he and his colleagues rely on data on avian flu transmission from bird to bird, bird to animal, and animal to human.
Dr. Philip Landrigan, director of the Program for Global Public Health and the Common Good at Boston College, said the pause robs states of information they need to understand the full picture of potential health risks.
“You are not able to control disease if you don’t know how many cases there are, and if people are sick and dying,” he said. “That is essential for developing a disease control system, whether it’s bird flu or measles.”
Brown, the state’s epidemiologist, called the two-week pause “disappointing” but added it is unlikely to significantly decrease the department’s ability to understand and track bird flu in Massachusetts.
The department, she said, has “routine communications with other states in the Northeast about many public health concerns, including a standing bimonthly meeting that’s specifically about avian flu and that includes both public health and animal health officials, and these communications are helping us maintain situational awareness.”
The bird flu — also known as highly pathogenic avian influenza, HPAI, or H5N1 — has likely killed wild birds in Boston, Amherst, and Plymouth in recent weeks. Officials closed a park in Brockton Friday after finding dead swans and Canada geese in a park pond.
Andrew Vitz, the state ornithologist with MassWildlife, said there is evidence that the virus is now “widespread” in the state among wild water birds. The state’s Executive Office of Energy and Environmental Affairs said in a statement the virus is “likely present even in places where there has not been a confirmed positive.”
The more the virus spreads, the greater the chance it will acquire genetic changes that would make it transmissible among humans.
This year’s harsh winter could be behind the spread of bird flu, experts said. Because there is less open water, due to frozen lakes, ponds, and reservoirs, birds are congregating in fewer more crowded areas and potentially transmitting the virus more easily.
Vitz said infections are concentrated around greater Boston and the southeast while Central Massachusetts and the Connecticut River Valley have fewer suspected cases.
“It’s important to understand that both wild and domestic birds can become infected with HPAI,” he said. “Raptors, waterfowl, and other aquatic birds are most at risk for infection, although any bird species should be considered susceptible to the virus.”
Since the current subtype of the virus was introduced to the US in late 2021, 145 million birds and more than 940 cattle have been infected, Brown said. Yet, there have been just 68 total reported human infections nationwide and no infections reported in Massachusetts.
“This is an animal virus right now,” she said. “While it can occasionally infect humans, it has not mutated in a way where it can infect people easily.”
The bird flu hasn’t reached New England cattle herds. Ashley Randle, the commissioner of the Massachusetts Department of Agricultural Resources, said the state has “consistently” tested the milk supply among licensed dairy farms since August and has achieved “100 percent negative results for HPAI.”
Randle added that evidence has shown that milk pasteurization kills the virus, so “both meat and pasteurized milk are safe to consume.”
The bird flu has broken out at farms in other states, disrupting the nationwide supply of eggs and causing local shortages and price increases.
“A lot of that is impacting the large commercial operations — that’s where we’re seeing the increase in egg prices that is impacting consumers’ ability to afford eggs," Randle said.
Brown said the main advice now for the public, in addition to staying away from wildlife, is to report groups of five or more dead birds at a single location to the Division of Fisheries and Wildlife and notify the state’s Division of Animal Health of possibly infected poultry.
Vitz said that some infected birds may not show symptoms of infection but can still transmit the virus. Animals that scavenge birds, such as foxes, are also more likely to have bird flu. He advised that dogs should be leashed and that cats should be kept inside.
Randle suggested people with backyard flocks or poultry operations eliminate standing water and restrict their animals’ access to ponds and streams.
“Biosecurity is incredibly important on farms and for backyard flocks, and we recognize how emotionally and financially devastating [bird flu] can be for flock owners,” Randle said.
Emily Spatz can be reached at emily.spatz@globe.com. Follow her on X @emilymspatz. Kay Lazar can be reached at kay.lazar@globe.com Follow her @GlobeKayLazar. Robert Weisman can be reached at robert.weisman@globe.com.