The ongoing outbreak of “bird flu” has spread widely across both wild bird populations and commercial poultry operations …
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![Laying hens are at risk from the H5N1 avian virus, which is highly contagious for chickens. [Courtesy photo]](/uploads/original/20200820-155007-chickens.jpg)
The ongoing outbreak of “bird flu” has spread widely across both wild bird populations and commercial poultry operations, raising concerns for animal health, food production, and the broader economy. On Jan. 31, SciLine hosted a panel of experts to share insights into the outbreak’s scale, what is driving the spread and economic impacts.
Some key takeaways from the briefing:
This strain of the avian influenza virus was first detected in birds in 1996 and has spread globally since then, due in part to trade that was not monitored for biosecurity, Dr. Carol Cardona, of the University of Minnesota, explained. The outbreak in the United States started in 2022. It has spread to all 50 states. The virus is highly contagious in domestic poultry.
Wild waterfowl such as migratory ducks and geese are the primary carriers of this virus, said Dr. Maurice Pitesky, of the University of California, Davis. “Unfortunately, dairy and poultry infrastructure overlaps with areas waterfowl live in the winter,” he continued. Development in former wetland areas has also caused waterfowl to nest closer to farms.
“We’ve lost a lot of our natural wetlands, where ducks and geese spend 14 hours a day,” he said. Pushed out of their natural habitat, the waterfowl now use dairy ponds, flooded rice fields and other areas flooded by rain.
Waterfowl might be nesting at one farm one day and another farm the next day, he said.
“When birds go on their feeding flights, they can spread virus to other areas,” he continued. The bird poop, which could contain the virus, can be spread on the feet of rodents and tracked into barns.
Milk and meat from infected animals pose no risk to consumers if food is properly prepared, the experts stressed. For milk, that means pasteurization, which kills the virus. For eggs and meat this means heating to the temperature recommended for food safety by the USDA. The USDA recommends a minimum internal temperature of 165 degrees Fahrenheit for chicken and eggs; and, 145 degrees for beef.
The virus has crossed over into mammals. H5 has been found in dairy cattle, foxes, bears, domestic cats, tigers, rabbits, humans, raccoons and more.
The virus has wiped out millions of chickens in the United States. Infections in cattle may result in reduced milk production.
“Veterinarians are very concerned about the cats,” said Cardona. “Cats go between a feral state where they live on farms to a very domesticated house pet state,” she continued. The felines may interact with the poultry or cattle and then infect the human population.
She said they are also concerned about the mice infection, which happened recently. “We’ve seen that H-5 breaks all the rules. It has been detected in mice on some cattle farms,” she said.
Some countries vaccinate poultry, said Cardona. The United States does not.
“In the United States, we said back in the 70s or 80s that we wouldn’t vaccine for Highly Pathogenic Avian Influenza and would not trade with countries that did,” she explained. “At that time, we had much less knowledge about the types of surveillance you would have to do to make sure you weren’t bringing in the virus with an immunized bird.”
The concern was that an immunized bird could still carry the virus, she explained.
“Today we have held on to that protective ideology,” she continued.
Cardona said the hesitation to vaccinate comes from the broiler part of the poultry industry. Farmers who raise broilers don’t want to immunize chickens due to trade restrictions, she said.
“France is immunizing now,” she said. “We’re often the first to cast that political stone and pull out of trade agreements.”
The entire globe has H5 except New Zealand, said Cardona. “We have to all come together to fight this virus.”
“As a veterinarian it’s very important that this is a tool that can be used to protect birds, to protect humans from spillover cases, to protect cattle,” she said. “I’m very pro immunization.”
Pitesky said more coordination is needed among countries.
“What’s going on in southeast Asia, what’s going on in the Middle East, what’s going in Europe, those detections matter to us,” Pitesky said.
For example, he said the United States and Canada are tracking infections in separate data bases.
“We need to move toward sharing the data,” he said, noting there is a “lot of siloing going on.”
He said countries should also share data on the efficacy of vaccine use.
The virus could continue to cost the United States billions of dollars.
“It impacts the birds that are laying the eggs and then we have a supply shortage and that leads to higher prices,” said Dr. Jada Thompson, of the University of Arkansas. It also impacts the breeding program.
“When we start thinking about the cost of an outbreak, we see the change in retail prices for eggs at the grocery store,” said Thompson. More costs come from replacing flocks, additional biosecurity, testing, and monitoring. “The costs aren’t just the direct ones we can see, they are all up and down the supply chain and multiplied along the line,” she continued.
“Prices aren’t going to recover tomorrow, but they are going to recover,” said Thompson. “Things are not going to change overnight. This is going to be ongoing until this disease is controlled.”
Migrating birds that have been infected in their northern nesting grounds shed the virus as they travel south, Cardona explained. “The migratory birds at the top of the flyway are shedding more viruses than they are at the bottom,” she explained. “Ninety percent of the cases are across the northern part of the United States. A lot of that has to do with some of this exposure.”
Pitesky said farmers can use biosecurity measures to reduce the spread of the virus. “They can look at things like the ventilation system, whether the farm or barn has curtains. They should look at outward facing biosecurity and inward facing security,” he said. “Ninety percent of efforts in the past have been focused on internal security.”
According to the Centers for Disease Control , most human cases of flu caused by the H5 in the United States have been mild, so far, and most were in people who had known exposure to sick or infected animals. The severity of illness associated with flu has ranged from mild to severe. According to the CDC website, "as of Jan. 6, 2025, there were 66 confirmed human cases of H5N1 bird flu, including one death, in the United States since 2024 and 67 since 2022."
The reported symptoms of bird flu in humans vary. Eye redness has been the predominant symptom among recent U.S. cases of the virus infection. Respiratory symptoms and fever were also reported.
Symptoms usually start with normal flu-like symptoms, including:
SciLine is a free service for journalists and scientists based at the nonprofit American Association for the Advancement of Science (AAAS), the world’s largest multidisciplinary scientific society. Editorially independent, nonpartisan, and funded by philanthropies, SciLine has the singular mission of enhancing the amount and quality of scientific evidence in news stories.
According to University of Florida Institute of Food and Agricultural Services (UF/IFAS), the Florida poultry industry has about 78.5 million broilers and 11.3 million layers.
Broilers are chickens raised for meat production. The breeds raised for broilers are known for their rapid growth. A broiler is usually processed for meat at 6 to 8 weeks of age and weighs around 4 pounds when it is sent to market.
Layers are chickens raised for egg production. The breeds chosen for layers can lay about 300 eggs per year. Pullets (young hens) start laying when they reach 20-24 weeks. The average lifespan of a laying hen in Florida is between 3 to 7 years, but with ideal care they can reach 10 years. Most commercial hens are culled (and may used for pet food) after 3 years, as their egg production decreases after this time.
