Topline
Scientists have proven how cows have spread H5N1 bird flu across the country and infected other cows, wild birds and even mammals like cats and raccoons, according to research published in Nature Wednesday, findings that suggest it may be capable of spreading effectively between people in the future as outbreaks on poultry and dairy farms spark concerns the virus could trigger a pandemic in humans.
Cows are spreading bird flu in the U.S., researchers found.
Key Facts
Using genomic data, computer modeling and data about the virus’ spread, researchers from Cornell University have shown how infected cows from Texas spread H5N1 avian influenza to a farm with healthy cows in Ohio, as well as to cats, a racoon and wild birds in the area.
It is one of the first times scientists have seen “evidence of efficient and sustained mammalian-to-mammalian transmission” of the H5N1 bird flu strain, said Diego Diel, an associate professor of virology at Cornell and one of the study’s authors.
While it primarily infects birds, the so-called highly pathogenic avian influenza strain is capable of infecting mammals—including humans—and Diel said repeated spillovers into mammals from birds or transmission between mammals raises the risk of the virus mutating in a way that “could lead adaptation to mammals, spillover into humans and potential efficient transmission in humans in the future.”
This H5N1 strain is particularly capable of targeting and infecting cells for the mammary gland, a specialized gland that produces milk and is unique to humans and other mammals, the researchers found, and milk from infected animals contained high quantities of the virus.
Genetic data showed the infected cows transmitted the virus to cats and a racoon found dead at affected farms, likely through drinking raw milk from infected cows, as well as wild birds, which the researchers suspect were infected from environmental contamination or aerosols kicked up during milking or cleaning.
While the data clearly showed evidence of mammal-to-mammal transmission, genetic analysis did not reveal signs that would lead to enhanced transmissibility in humans, Diel said, though he said it is crucial to keep monitoring the outbreak for signs the virus is adapting to mammals.
How Worried Should We Be About A Human Bird Flu Pandemic?
Before COVID-19, experts widely believed an influenza virus would be responsible for the next human pandemic. There have been four influenza pandemics since1900, including the 1918 Spanish Flu, and seasonal variations of the virus still sicken and kill millions of people every year. Influenza viruses are expert shapeshifters, mutating constantly in a way that helps them skirt our body’s defenses and survive the drugs we may have developed to fight them. It can also help them acquire different ways to infect existing hosts, as well as to find new hosts. This is why we need seasonal shots to protect against new circulating variants and why experts are worried about more major shifts that can trigger a pandemic. H5N1 has long been a concern to health officials and agencies like the World Health Organization and the Centers for Disease Control and Prevention have designated it a pathogen of pandemic potential. Though it has only sporadically infected humans, usually after close contact with infected animals, it has still infected more than 800 people since 1996.
How Bad Is The Bird Flu Outbreak In The U.s.?
While it has torn through wild and domestic bird populations for years, experts consider increasing spillovers into mammals in recent years to be of “ enormous concern.” Scientists worried about outbreaks in marine animals like seals and sea lions, and the virus has been found in a wide array of mammals including dolphins, mink, dogs, goats, squirrels and polar bears. Outbreaks among cattle in the U.S. marked a particularly worrying turning point and have intensified concerns. The type of virus had not been documented in cows before and it shocked many scientists who did not think the animals were susceptible to it. A good deal about the outbreak is still unknown, however—experts have criticized officials’ failure to share crucial information and lax testing requirements, which they claim risks outbreaks growing unnoticed—and genetic data has divided scientists as to whether H5N1 is adapting to better infect humans. The intensive nature of cattle farming raises fears the virus could gain a foothold in mammals outside of bird populations, as well as spread the virus to humans working with them and consuming products like milk and beef. Officials stress the risk to humans from bird flu is low and monitoring for the virus on farms and in milk has been stepped up to look for signs it may be adapting to mammals like humans as hosts.
What To Watch For
The federal government has a stockpile of potentially effective vaccines to stave off pandemic bird flu but is tapping industry to develop more shots targeted towards the H5N1 circulating. Moderna in July received $176 million in federal funding to develop an mRNA bird flu vaccine in preparation for a human pandemic. GSK is also developing a bird flu mRNA vaccine after it acquired the product from German biotech CureVac.
Big Number
11. That’s how many human cases of H5 bird flu have been reported in humans in the U.S. during the current outbreak that began in 2022, according to the CDC. H5 is a broader category of virus and these infections are all believed to be the kind of H5N1 circulating in animals, though only five have been confirmed as such. All infections follow close interactions with presumably infected animals, the CDC said, four after exposures to dairy cows and seven to poultry. In that time, more than 100 million domestic birds have been affected, at least 9,555 wild birds and 168 dairy herds. Hawaii is the only U.S. state without confirmed H5N1 infection in wild birds, poultry or animals.
Tangent
A man in Mexico died after contracting another strain of avian influenza, H5N2, in June. It was the first time the virus, separate from the H5N1 spreading among cattle, had been seen in humans and raised more questions over bird flu’s ability to reach humans. The WHO said the man had no history of exposure to poultry or other animals and it is not clear where the man may have been exposed to the virus. The agency said the risk posed by H5N2 is low and there have been no further cases reported following an investigation.
Further Reading
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