Health officials are calling for new vigilance against avian flu, but some experts are confused as to why reporting new human cases has stopped.
Are government cuts weakening searches for cases? Are immigrant farm workers who have described many cases in the United States afraid to move forward for testing amid the Trump administration’s deportation? Is the natural decline of infection?
“I don’t know why there were no cases,” said Jennifer Nuzzo, director of Brown University’s Pandemic Center. “I think we should assume that no infections occurring in farm workers have been detected.”
H5N1 bird flu has been widely spread among wild birds, chicken and other animals around the world for several years, and became a problem with people and cattle in the US early last year
Over the past 14 months, 70 people in the US have been reported to be infected. Most of them are dairy and poultry farm workers. One person died, but most of the infected people were mildly ill.
The most recent infectious disease confirmed by the Centers for Disease Control and Prevention took place in Nevada, Ohio and Wyoming in early February.
California was a hot spot, with three-quarters of the dairy cow country’s infectious diseases. But people’s tests and cases have fallen. At least 50 people were tested each month in the second half of 2024, but three in March and one in April, and so far in May. Overall, the state confirmed H5N1 infections in 38 people, but none since January 14th.
In a call with a US doctor this month, a CDC official noted that avian influenza is seasonal. Cases peak in autumn and early winter, perhaps due to the migration patterns of wild birds, the major spreader of the virus.
That could mean that the US is experiencing a natural, perhaps temporary-reduction of events.
It is unlikely that severe human infectious diseases requiring hospitalization will be noticed, said Michael Osterholm, an expert at the University of Minnesota infectious diseases.
Furthermore, patchwork systems that monitor viruses in sewage and wastewater suggest that recent activity is limited.
New infections are still being detected in birds and cattle, but not as often as many months ago.
“It’s not surprising that human cases have also decreased given the fact that the number of animal detections has decreased, according to USDA data,” the CDC said in a statement.
Dr. Gregory Gray said he was not worried that the CDC had not identified any new cases on the month.
“I don’t think anyone is hiding anything,” said Gray, an infectious disease diagnoser at the University of Texas Medical Chapter in Galveston.
However, some Osterholm and other experts believe that at least a mild infection is likely to be undetected. And they worry that their efforts to find them are being eroded.
The resignation at the U.S. Department of Agriculture and Food and Drug Administration’s veterinary center could delay government surveillance for avian flu, said Keith Poursen, director of the Wisconsin Veterinary Diagnostics Institute.
Three of the 14 experts accepted an offer of resignation that was postponed by the National Institutes of Animal Health Network. They are one of more than 15,000 USDA staff members who accept the offer, a spokesperson for the agency said.
Dozens of staff have also been fired from the FDA Veterinary Institute’s investigation and response network. This investigated animal diseases caused by problems involving contaminated pet food. Cats from several states became ill and died after eating raw pet food, which was found to contain H5N1-infected poultry.
“Since Trump took office, target surveillance has really fallen sharply,” said Angela Rasmussen, a virologist at the University of Saskatchewan in Canada.
She wonders if immigrant farm workers are too scary.
“We cannot argue with anyone who is at risk of being shipped to a Salvador glug to report exposure or ask for testing,” she said.
The CDC says the risk to the general public remains low
The CDC characterizes the risk to the public as low, but it is higher for people who work with cattle and poultry and are in contact with wild birds.
Earlier this month, an agency’s assessment said there is currently a “moderate risk” that the avian flu circulatory system could cause a future pandemic, but the CDC emphasized that other new forms of avian flu have been labelled similarly in the past.
Still, research continues.
Scientists at Texas A&M University have collected blood samples from dairy workers from multiple states to test signs of past H5N1 exposure, said David Douprate, a workplace health and safety expert who leads the project. The one-year survey is funded by a grant of nearly $4 million from the CDC and is expected to close in July.
Douphrate said it utilized its 20-year relationship with dairy producers and workers to access the farm.
“We’ve been a very good attendance,” Dooparreto said. “They are very pleased.”
Similar surveillance is “urgently needed” among cats, says Kristen Coleman, a researcher at the University of Maryland College Park, is studying a new animal disease. She recently released a paper reviewing the infectious diseases of cats between 2004 and 2024.
The barn cat who died after drinking raw milk was one of the first signs of a dairy cow’s contracting avian flu in 2024. Since then, the Agriculture Bureau has identified more than 120 domestic cats that have been infected with the virus in the United States.
Infectious diseases are primarily found in dead cats. Not much is known about mild infections, whether cats can recover from avian flu, or whether the virus can spill on people.
Coleman has collected blood samples from American cats to see if there is evidence of previous exposure to the virus. However, this process is slow and research funding is uncertain.
“It’s easy to downplay something because that’s what humans usually do,” she said. “But all we really need to do is ramp up.”