It's now official: the highly pathogenic bird flu A(H5N1) that's been spreading across the globe since 2020 has now been passed from a cow to a dairy farmer in the US, the first confirmed cow-to-human transmission of this virus on record.
The good news is the case was caught quickly and the virus manifested as inflammation in the eye, rather than any type of upper respiratory infection. So the chances of it having been passed on to anyone else, if human-to-human transmission is even yet possible, are lower.
What's more, after nervously watching it spread through poultry and wild animals, we've now got some solid data on how the bird flu presents in humans, which should help experts in assessing the threat to public health and in identifying more cases if and when they appear.
"It's a huge thing that the virus has jumped from birds to mammals, dairy cows in this case, and then to humans," says environmental toxicologist Steve Presley, the director of the Biological Threat Research Laboratory at Texas Tech University.
Presley and his colleagues are behind the newly published paper on this one case of cow-to-human bird flu transmission, confirmed in tests carried out in highly biosafe laboratory conditions, and shared with the US Centers for Disease Control and Prevention (CDC).
The farm worker reported redness and discomfort in their right eye towards the end of March 2024. Though they hadn't been in contact with birds or poultry, they were working with cows some of whom had been showing signs of sickness.
It's only recently that this bird flu passed from poultry to livestock in the US, which was something of a surprise for experts because it was the first time ever that highly pathogenic avian influenza (HPAI) had been detected in dairy cattle. Closer monitoring of dairy cows and those who come into contact with them will now be required.
This is only the second human case of this bird flu in the US, and human-to-human transmission hasn't been observed anywhere yet. But each time the pathogen finds a human host, it has more chances to adapt and mutate to be more infectious to our species which seems to have happened in this case.
"The virus identified in the worker's specimen had a change (PB2 E627K) that has been associated with viral adaptation to mammalian hosts and detected previously in humans and other mammals infected with HPAI A(H5N1) viruses and other avian influenza A virus subtypes," Presley and his CDC and Texas state health authority colleagues write in their paper.
The current bird flu outbreak started in 2020, and although human infection is rare, there's a high mortality rate. That means it's vital that we understand how disease is being passed between animals, and where this is happening.
We know it's now in a host of mammals, including foxes, seals, sea lions, bears, and domestic cats. With the stakes so high, and the pandemic fresh in people's minds, scientists are working overtime to try and minimize the ongoing spread of the influenza.
"[This study is] going to lay the foundation, I believe, for a lot of research in the future of how the virus is evolving," says Presley.
The research has been published in The New England Journal of Medicine.
Bird flu is spreading into unprecedented territory in the United States, infecting scores of cows at dairy farms in nine states and jumping to one farm worker only the second confirmed case ever of a human getting infected by the H5N1 virus within the United States. Federal and local agencies are working to monitor and curtail the spread of H5N1. We asked scientists who study bird flu what we know about the virus and how it might be kept at bay or could expand into the next pandemic.
Avian flu is, as its name suggests, most commonly found in wild and farm birds worldwide, with periodic outbreaks occurring among mammals. H5N1, a particular strain of bird flu, periodically flares up more expansively; it was cited for causing more than 100 million bird deaths globally in 2022 and has been detected in dozens of species of mammals. In the United States, the virus has been detected in more than 200 different mammals, including cats, goats, and raccoons.
Most often, the virus gets transmitted when one animal eats an infected animal or comes in contact with bodily materials like feces and saliva from an infected animal, as explained by the Centers for Disease Control and Prevention (CDC).
Avian flu viruses rarely infect humans. The World Health Organization (WHO) reports that from 2003 to April 1, 2024, 23 countries reported a total of 889 human cases of H5N1. The most common symptoms in people, according to the CDC, include eye redness (conjunctivitis), respiratory difficulties, fever, cough, sore throat, and pneumonia.
However, more than half of the worldwide human cases (463) resulted in death. It is a highly pathogenic strain, explains Erin M. Sorrell, PhD, MSc, senior scholar at the Johns Hopkins Center for Health Security and associate professor at Johns Hopkins Bloomberg School of Public Health in Maryland. It has the ability to replicate outside the traditional locations where low-pathogenic influenza does: the intestinal tract for poultry; the upper and lower respiratory tracts in humans. The virus becomes systemic in its infection.
In the United States, the first known case of transmission to a human occurred in 2022. The CDC says that person, who worked directly with infected poultry, reported mild fatigue and recovered.
The second known case was reported in March 2024, in a dairy farm worker in Texas. The only symptom was conjunctivitis in both eyes, which receded, according to a case assessment by the CDC and Texas health agencies.
As of now, this is a low-risk situation for humans, says Michael Osterholm, PhD, MPH, director of the Center for Infectious Disease Research and Policy at the University of Minnesota. But that could change as the virus spreads among more animals, he warns.
There are varying levels of concern among scientists who are watching the outbreak. One reason for that concern is that it has begun spreading to dairy cows animals that have a lot of close contact with humans.
Dairy cows do not normally get infected with Influenza A viruses, which is what bird flu is, says Jenna Guthmiller, PhD, assistant professor in the Department of Immunology and Microbiology at the University of Colorado Anschutz School of Medicine.
The assessment of the Texas case notes that the worker reported no contact with sick or dead wild birds, but direct and close exposure to dairy cows. Some of those cows showed signs of illness that had been appearing at other dairy farms in the area, including decreased milk production, reduced appetite, lethargy, fever, and dehydration. A map from the U.S. Department of Agriculture (USDA) shows the states where the virus recently has been found.
Tests of cattle in the area where the worker got infected determined that the bovine outbreak started when a wild bird infected a cow at a Texas farm in December, perhaps through bodily secretions into the cattles food or water supply.
The concern is that cows might become hosts that spread the virus to humans, Guthmiller says. That spread can occur a number of ways, including through milk from the udders that farm workers could absorb through their eyes, nose, or mouth.
So far, the risk of humans getting infected is low, the CDC states in summaries about H5N1. But Rick Bright, PhD, former deputy assistant secretary for preparedness and response at the Department of Health and Human Services (HHS), says that because the virus is spreading among both birds and cows on farms where people work, the opportunity for infecting a human is increasing.
In the milking parlor of a farm, people work extremely close to the cows udders, even if they are primarily guiding the milking machines.
Your face, your shoulders, your head are at the level of the cows udders, says Guthmiller, who milked cows on the dairy farm where she grew up. We are literally putting our faces right where the flu viruses are coming out.
If a milking machine gets infected with the virus from one cow, the infection can be spread to other cows and to workers who use the same machine.
The main transmission that people believe is occurring is through these milkers becoming contaminated, then moving on to the next cow, Guthmiller says. She says it would add significant time and cost for a farm to try cleaning the milkers after each cow.
It seems that this virus is transmitting [from cow to cow] before cows even show any symptoms, or their symptoms are mild, Guthmiller says. Cows cant tell us that theyre not feeling well.
Data that signal warning signs of an illness, like decreased production from a few cows, take a long time to come to the notice of managers who are monitoring hundreds or thousands of cows. Meanwhile, humans and animals continue to have close contact with infected cattle.
Cows are routinely traded between farms. Theyre going from one farm to another, which could lead to outbreaks on more farms, Guthmiller says.
In April, the U.S. Department of Agriculture (USDA) mandated that dairy cows receive a negative test for Influenza A before being transported to another state.
The poultry industry has dealt with avian influenza for years, says Sorrell at Johns Hopkins. The common responses include culling entire flocks to stop the spread.
The dairy industry has no experience with testing and responding to cows with avian flu. It is much easier, faster, and cheaper for poultry farms to buy and raise new birds than for a dairy farm to do the same with cows, Sorrell explains.
Scientists are still learning about the extent of the disease and how it is being transmitted on farms.
We dont know how many cows are infected, we dont know how many people have been exposed, says Bright, now chief executive of Bright Global Health, which focuses on responses to public health emergencies.
Getting the answers requires surveillance of animal and human populations no easy task. Disease surveillance in the United States is a fractured and uneven endeavor, carried out mostly on a voluntary basis by state and local governments with guidance and prodding from federal agencies.
Scientists who have been critical of the federal effort say surveillance should include more testing of farm workers and cattle. But for various reasons (including lack of trust in government regulators), workers and farm managers are wary of government officials conducting tests. The tests could also help discover viral mutations that might facilitate the spread of the infection among humans.
Bright worries that by the time the virus is confirmed in even a small number of people (say, 10), it will have spread so widely that an epidemic might be at hand. Some scientists speculate that more dairy farmers already have become sick, but havent been tested for H5N1.
If we havent caught the virus before it mutates to efficiently transmit person-to-person, all bets are off in terms of being able to control it, Bright says.
Farm workers could wear personal protective equipment (PPE) such as gloves, goggles, and masks but PPE is rare on dairy farms. (The infected worker in Texas reported wearing gloves.)
Most diseases of cows dont affect humans, so theres very little biosecurity on dairy farms, Guthmiller says. Were not concerned with getting something from the cows.
Plus, PPE is especially uncomfortable and inconvenient in a milking facility. Masks impede breathing and get soaked from sprayed milk. Goggles get sprayed as well and they decrease visibility. People arent wearing safety glasses, Guthmiller says. That would be an annoyance.
The CDC has asked local jurisdictions to offer PPE to dairy farms. Reports are that few farms have taken up the offers.
Pasteurized milk does not transmit H5N1 and is safe to drink, the FDA says. The conclusion is based on repeated qPCR (quantitative polymerase chain reaction) tests of pasteurized milk and other pasteurized dairy products (including cottage cheese and sour cream) that showed no live, infectious bird flu virus. The agency said that fragments of the flu were found in some samples, but that those fragments had been inactivated by the pasteurization process.
Influenza viruses are very sensitive to heat from the pasteurization process, which kills them, Sorrell says.
On the other hand, raw milk, which has not gone through that process, is not protected from the virus, Sorrell explains. A study of cats that got sick or died from H5N1 this year concluded that they had been infected by drinking unpasteurized milk from the cows on dairy farms.
The USDA conducted testsof commercially sold ground beef in states where H5N1 had been confirmed in cattle. No samples have shown traces of H5N1.
The United States has two candidate vaccines available to manufacturers for the production of a vaccine against H5N1 if an outbreak occurs among humans, according to the CDC.
Some scientists are not convinced that vaccine production could ramp up quickly enough to meet the need. Bright notes that the vaccines are produced through the decades-old process of injecting a virus into eggs, then harvesting the fluid to create an inactivated virus. Its a slow process.
Some scientists, including at the University of Pennsylvania Perelman School of Medicine, are exploring the use of mRNA technology to speed up production of a vaccine for bird flu, in much the same way as some COVID-19 vaccines were quickly developed.
Bright and Osterholm note that adjusting vaccines to address mutations of a virus is a perpetual challenge. Anything we have in the stockpile right now may not even come close to matching up with the new virus, Osterholm says.
In early April, the CDC sent a health advisory to clinicians and state public health departments to consider the possibility of H5N1 infection in patients who develop respiratory illness or conjunctivitis, and who had been exposed to potentially sick or dead birds or livestock.
The USDA and HHS have instituted several ways to financially support farms to help curtail the spread of H5N1, including reimbursing them for PPE, for costs of testing and treating their cattle, and for lost milk production in herds affected by the virus.
The CDC is working with state and local health departments to monitor people exposed to infected cattle, and is boosting its analysis of data about Influenza A among people, including in wastewater samples and emergency room visits.
For a person who does become infected by the virus, the CDC recommends antiviral drugs that are used for influenza.
Despite these and other steps, some scientists worry that government agencies are not doing enough to monitor the often-invisible spread of H5N1. The thing that is a concern to me is the lack of [widespread] testing of animals and milk on farms, Guthmiller says. By not having a better grasp of this outbreak, it could get a lot worse for dairy cows, for our food chain, and could have the potential to jump into a pandemic.
A flurry of reports about the genetics of the bird flu currently infecting U.S. cattle are offering insight into how the virus has and continues to spread. Since it first emerged in late 2020, this particular type of bird flu has infected a dizzying array of bird species, about 20 mammal species and some people (SN: 3/6/23; SN: 4/3/24). But transmission from cow to cow and from cow to person and other animals is new.
Now researchers tracing the family tree of the H5N1 avian influenza virus say that the outbreak in cattle, first reported in late March, probably started in late December 2023 (SN: 4/25/24). Cases of low milk production a symptom of infection in dairy cows in the Texas panhandle were reported in late January and early February. The U.S. Department of Agriculture confirmed the H5N1 diagnosis on March 25.
Since then, the virus has spread to dairy cows in at least nine U.S. states. A dairy farm worker in Texas got an eye infection, presumably from contact with sick cows. And genetic remains of the virus have been found in grocery store milk, suggesting the outbreak is widespread.
Mia Kim Torchetti, a veterinarian who directs the USDAs Diagnostic Virology Laboratory at the National Veterinary Services Laboratories in Ames, Iowa, says she had hoped this incursion could be stamped out quickly, but as detections in birds and mammals pile up, I have rapidly lost hope.
Though all public health agencies consider the risk of the bird flu spreading widely in people to be low, the outbreak is still reminiscent of the early days of the COVID-19 pandemic.
In that case too, researchers had used genetic analyses to determine that the outbreak had started long before cases were recognized (SN: 1/29/20). And as with COVID, preliminary data are coming out in press releases and preprints without first going through peer review. That doesnt mean the results arent trustworthy, but it does suggest we are in the early days and conclusions may change. The early data also point to myriad versions of influenza viruses preceding the cattle outbreak, just as many waves of SARS-CoV-2 variants caused peak after peak of COVID cases.
We often call the avian influenza virus currently infecting cattle by its nickname, H5N1 bird flu. But its full name is highly pathogenic avian influenza A H5N1 clade 2.3.4.4b genotype B3.13.
That specificity denotes the virus place in its family tree. Highly pathogenic avian influenza A H5N1 viruses which are deadly to chickens and related birds are a huge family tree of bird flu viruses. They all have the H5 form of hemagglutinin, a protein that latches onto host cells so the virus can infect them. The first highly pathogenic avian influenza H5N1 virus was found in 1996. Since then, scientists have documented the trees expansion, with some limbs dying off and others making it big. One successful limb of the tree is clade 2.3.4.4b. It has sprouted branches of its own, including genotype B3.13.
Various H5N1s have winged their way around the world after infecting wild birds. A different version crossed the Atlantic in 2014 and caused an outbreak in North American poultry in 2015, but it didnt take hold, Torchetti says. This time is different.
Clade 2.3.4.4 viruses have been infecting poultry and wild birds for several years. But the limb of the tree were dealing with now H5N1 clade 2.3.4.4b emerged in Europe in October 2020 when two bird flu viruses swapped parts. It came to the Americas in 2021. It has killed more than 90 million birds in the United States since January 2022, including wild birds and commercial poultry and backyard and hobbyist flocks that were culled when the virus was detected.
Influenza viruses are all about the swap meet.
Instead of one long novel, the genetic instruction books of influenza A viruses are more like a series of eight novellas, known as gene segments. Each segment carries one or more of the 11 genes that the virus needs to infect host cells and copy itself. When people, birds or other animals are simultaneously infected with more than one type of influenza virus, the viruses may exchange segments and thus create a new type of virus. This process called reassortment has resulted in pandemic strains of flu, including the 1918 influenza pandemic and 2009s swine flu (SN: 5/22/09).
Viruses cant swap parts willy-nilly. Not all combinations are compatible with each other. But whats unusual about this clade of H5N1s is that it undergoes reassortment far more often than earlier relatives, Torchetti says.
In wild birds in the Americas, this interchange of genes has been occurring for the last almost 24 months among H5N1 and other bird flus, says Rafael Medina, a virologist at Emory University School of Medicine in Atlanta.
Torchetti and colleagues have found more than 100 genotypes in clade 2.3.4.4b, mostly generated by reassortment. About 20 of those genotypes managed to spread among wild birds, poultry and the occasional other wild animal, the researchers reported May 1 in a preprint posted at bioRxiv.org.
One such reassortment happened shortly before the start of the cattle outbreak, scientists reported May 3 at Virological.org. Genotype B3.13 is a mix of four gene segments from the H5N1 that arrived from Europe in 2021 and four gene segments from a low pathogenicity bird flu from North America. (Low pathogenicity viruses arent usually deadly and may not produce any symptoms in infected birds.) It shows up relatively rarely among the viruses sampled in birds, Torchetti says. The B3.13 genotype is actually not common. The cattle have made it common. In fact, if predicting which virus might spillover into cattle based on prevalence in wild birds, this one was a little bit of an underdog, she says.
All the dairy cattle that have tested positive for H5N1 bird flu have this genotype, suggesting that the virus made the leap from birds to cows just one time. That probably happened in Texas toward the end of last year, Torchetti and colleagues as well as the team posting to Virological.org conclude.
Of the four gene segments the B3.13 genotype picked up, one produces an enzyme that helps copy the virus and the other makes a protein that encases the virus RNA. These specific gene segments have a role in the efficiency of virus replication, but scientists dont yet know whether that swap or other changes allowed the virus to more easily infect cattle or grow in mammalian cells, says Tavis Anderson, a research biologist at the USDA Agricultural Research Services National Animal Disease Center in Ames.
With COVID-19 variants, specific genetic changes led to new properties of the virus that made it more contagious or helped it evade the immune system (SN: 12/16/21; SN: 3/1/22). But theres no obvious indicator of that happening with the H5N1 currently spreading, Anderson says. In other words, B3.13 has been successful at replicating in cattle, but that may be more happenstance than thanks to any special properties of the virus.
No one knows exactly where, when and how the virus passed from wild birds into cattle.
Cows may have grazed on grass that wild birds carrying the virus pooped on, or the cows may have picked it up through contaminated feed or other livestock-bird interactions, Medina says. Its present at such a high levels in nature [that] the potential of spilling over into domestic animals is something that shouldnt surprise us anymore, he adds.
Once in cows, the virus started spreading from cow to cow. Theres now concern that cows could serve as mixing vessels for new varieties, much the way that pigs have been crucibles for the reassortment of avian, human and swine influenza viruses (SN: 5/14/24; SN: 2/12/10). USDA monitors influenza viruses in domestic swine and wild hogs but hasnt detected any H5 viruses in those animals, Anderson says.
Genetic signals suggest that cattle carrying the virus spread it from Texas to Kansas, Michigan and New Mexico. Theres also a genetic link suggesting that the cows from Michigan spread the virus to North Carolina, but the USDA researchers have found no record of cows moving between those states. More likely, these researchers say, cows that were moved from Texas to North Carolina spread the virus there.
Genetic analyses and shipment records confirm that H5N1 bird flu spread from Texas to other U.S. states, probably when infected dairy cattle with no symptoms were moved from state to state. The virus has been detected in nine states.
Since getting into cattle, the virus has jumped into other species including cats in Kansas and Texas that drank infected raw milk. More than half of infected cats from one north Texas dairy died within a few days of having the milk, probably because the virus went to the cats brains and nervous systems, researchers reported April 29 in Emerging Infectious Diseases.
The B3.13 genotype virus has also spilled from cows to raccoons, poultry and wild birds including blackbirds and grackle, researchers said in the Virological.org report. There were as many as five spillbacks from cattle to poultry and three from cows to wild birds, Torchetti and colleagues found. More spillbacks create more possibilities for swapping gene segments and thus more opportunities for a lethal or transmissible virus to emerge, possibly even one that could spread in people. Though agencies agree that risk to people is low, they have warned that human cases from exposure to an infected animal should be expected to pop up from time to time. And though there may be limited spread between people, such as family members, experts dont expect the virus as is to spread easily from person to person.
The Texas dairy farm worker who got an H5N1 eye infection was carrying a slightly different but closely related version of B3.13 from the one found in cows, researchers from the U.S. Centers for Disease Control and Prevention and colleagues reported May 3 in the New England Journal of Medicine. The person had contact with some dairy cows showing signs of H5N1 infection that were similar to symptoms in cattle at nearby farms with confirmed cases.
A veterinarian who works at multiple dairies in the Texas panhandle encouraged the worker to get tested for H5N1. They went to a Texas Department of Health field site but didnt reveal where they worked.
The worker is one of 13 people worldwide confirmed to have been infected with a clade 2.3.4.4b virus, and the only one thought to have been infected by a mammal. Some, including the dairy farm worker and a poultry farm worker diagnosed in 2022, have had no symptoms or mild ones. Others have developed severe or critical illnesses. One person in China died in 2022. The dairy farm worker got an antiviral medication called oseltamivir and has fully recovered.
A close look at the genetic makeup of the virus that infected the dairy farm worker revealed that it carried a mutation in a gene known to help the virus replicate better in mammalian cells. But without samples from cattle or other people on the farm, researchers have little information about the evolution of the virus in cattle and whether it can pass from person to person.
Its possible that the workers virus is a slightly earlier version of the one from cows, the CDC researchers say. That suggests that after first jumping from a wild bird into a cow, the virus spread more widely in cattle than previously thought. One twig of the B3.13 branch moved from Texas to other states. Thats the one that has been identified in cows and milk. Meanwhile, close cousins may have continued to quietly infect cows including ones at the workers farm.
Lets hope any callbacks to the early days of 2020 will end here. New regulations that went into effect April 29 governing the movement of dairy cattle and other measures may help contain the virus spread in cattle. So far, it hasnt turned up in the 30 samples of ground beef the USDA has tested. And the U.S. Food and Drug Administration announced May 10 that the latest round of nearly 300 samples of dairy products it tested did not contain the virus.
A wider outbreak in cattle might allow the virus to adapt to spread easily in mammals, including humans. One big thing coronavirus taught us is to never underestimate a virus, especially one that can change quickly.
Sales of raw milk appear to be on the rise, despite years of warnings about the health risks of drinking the unpasteurized products and an outbreak of bird flu in dairy cows.
Since March 25, when the bird flu virus was confirmed in U.S. cattle for the first time, weekly sales of raw cows milk have ticked up 21% to as much as 65% compared with the same periods a year ago, according to the market research firm NielsenIQ.
That runs counter to advice from the Food and Drug Administration and the Centers for Disease Control and Prevention, which calls raw milk one of the riskiest foods people can consume.
Raw milk can be contaminated with harmful germs that can make you very sick, the CDC says on its website.
As of Monday, at least 42 herds in nine states are known to have cows infected with the virus known as type A H5N1, federal officials said.
The virus has been found in high levels in the raw milk of infected cows. Viral remnants have been found in samples of milk sold in grocery stores, but the FDA said those products are safe to consume because pasteurization has been confirmed to kill the virus.
Its not yet known whether live virus can be transmitted to people who consume milk that hasnt been heat-treated.
But CDC officials warned last week that people who drink raw milk could theoretically become infected if the bird flu virus comes in contact with receptors in the nose, mouth and throat or by inhaling virus into the lungs. Theres also concern that if more people are exposed to the virus, it could mutate to spread more easily in people.
States have widely varying regulations regarding raw milk, with some allowing retail sales in stores and others allowing sale only at farms. Some states allow so-called cowshares, where people pay for milk from designated animals, and some allow consumption only by farm owners, employees or non-paying guests.
The NielsenIQ figures include grocery stores and other retail outlets. They show that raw milk products account for a small fraction of overall dairy sales. About 4,100 units of raw cows milk and about 43,000 units of raw milk cheese were sold the week of May 5, for instance, according to NielsenIQ. That compares with about 66.5 million units of pasteurized cows milk and about 62 million units of pasteurized cheese.
Still, testimonies to raw milk are trending on social media sites. And Mark McAfee, owner of Raw Farm USA in Fresno, California, says he cant keep his unpasteurized products in stock.
People are seeking raw milk like crazy, he said, noting that no bird flu has been detected in his herds or in California. Anything that the FDA tells our customers to do, they do the opposite.
The surge surprises Donald Schaffner, a Rutgers University food science professor who called the trend absolutely stunning.
Food safety experts like me are just simply left shaking their heads, he said.
From 1998 to 2018, the CDC documented more than 200 illness outbreaks traced to raw milk, which sickened more than 2,600 people and hospitalized more than 225.
Raw milk is far more likely than pasteurized milk to cause illnesses and hospitalizations linked to dangerous bacteria such as campylobacter, listeria, salmonella and E. coli, research shows.
Before milk standards were adopted in 1924, about 25% of foodborne illnesses in the U.S. were related to dairy consumption, said Alex OBrien, safety and quality coordinator for the Center for Dairy Research. Now, dairy products account for about 1% of such illnesses, he said.
I liken drinking raw milk to playing Russian roulette, OBrien said. The more times people consume it, the greater the chance theyll get sick, he added.
Despite the risks, about 4.4% of U.S. adults nearly 11 million people report that they drink raw milk at least once each year, and about 1% say they consume it each week, according to a 2022 FDA study.
Bonni Gilley, 75, of Fresno, said she has raised generations of her family on raw milk and unpasteurized cream and butter because she believes its so healthy and lacks additives.
Reports of bird flu in dairy cattle have not made her think twice about drinking raw milk, Gilley said.
If anything, it is accelerating my thoughts about raw milk, she said, partly because she doesnt trust government officials.
Such views are part of a larger problem of government mistrust and a rejection of expertise, said Matthew Motta, who studies health misinformation at Boston University.
Its not that people are stupid or ignorant or that they dont know what the science is, he said. Theyre motivated to reject it on the basis of partisanship, their political ideology, their religion, their cultural values.
CDC and FDA officials didnt respond to questions about the rising popularity of raw milk.
Motta suggested that the agencies should push back with social media posts extolling the health effects of pasteurized milk.
Communicators need to make an effort to understand why people consume raw milk and try to meet them where they are, he said.
The Associated Press Health and Science Department receives support from the Howard Hughes Medical Institutes Science and Educational Media Group. The AP is solely responsible for all content.
"Avian influenza A (H5N1)," "bird flu," and "H5N1 bird flu" all refer to an illness caused by influenza type A viruses, which primarily affect birds. H5N1 bird flu was first identified in geese in China in 1996 and in people in Hong Kong the following year. Almost 25 years later, in 2020, a new variant of H5N1, referred to as Highly Pathogenic Avian Influenza (HPAI), was detected in wild birds in Europe; it was first seen in birds in the U.S. and Canada in late 2021, and has since been detected in a variety of wild bird species in all 50 states.
(The term highly pathogenic relates to how the virus impacts birds, not necessarily humans. There is also a low pathogenic avian influenza [LPAI] that usually causes mild illness in birds and poultry; however, some LPAI strains can mutate into strains that can cause severe illness and even death in poultry.)
In February 2022, the virus began causing sporadic outbreaks of HPAI H5N1 in backyard and commercial poultry flocks in the U.S., causing serious illness and death in infected chickens. The number of outbreaks has increased and spread over timeas of May 2024, the CDC reported poultry outbreaks in 48 states.
In addition, there have been sporadic infections in mammals (including bears, bobcats, minks, mountain lions, raccoons, skunks, and others), according to the CDC. And now, as of early May, there have been outbreaks in dairy cattle in nine states.
In the two human cases in the U.S., neither involved person-to-person spreadboth people were infected after exposure to animals presumed to have bird flu. The most recent case, in April 2024, occurred in a dairy worker in Texas who became infected after being exposed to cows that were presumed to be infected, as described in a letter to the editor published in the New England Journal of Medicine in May.
The previous case, reported in April 2022 in Colorado, involved a person exposed to poultry also presumed to be infected, although this case may have been a contamination of the nasal passages with the virus as opposed to an actual infection, according to the CDC. Both cases in humans were mild, and both people recovered.
As researchers increasingly rely on wastewater testing to monitor the spread of bird flu, some are questioning the reliability of the tests being used. Above, the Hyperion Water Reclamation Plant in Playa Del Rey.
(Jason Armond / Los Angeles Times)
As health officials turn increasingly toward wastewater testing as a means of tracking the spread of H5N1 bird flu among U.S. dairy herds, some researchers are raising questions about the effectiveness of the sewage assays.
Although the U.S. Centers for Disease Control and Prevention says current testing is standardized and will detect bird flu, some researchers voiced skepticism.
Right now we are using these sort of broad tests to test for influenza A viruses in wastewater, said epidemiologist Denis Nash, referring to a category of viruses that includes normal human flu and the bird flu that is circulating in dairy cattle, wild birds, and domestic poultry.
Its possible there are some locations around the country where the primers being used in these tests ... might not work for H5N1, said Nash, distinguished professor of epidemiology and executive director of City University of New Yorks Institute for Implementation Science in Population Health.
The reason for this is that the tests most commonly used polymerase chain reaction, or PCR, tests are designed to detect genetic material from a specific organism, such as a flu virus.
But in order for them to identify the virus, they must be primed to know what they are looking for. Depending on what part of the virus researchers are looking for, they may not identify the bird flu subtype.
There are two common human influenza A viruses: H1N1 and H3N2. The H stands for hemagglutinin, which is an identifiable protein in the virus. The N stands for neuraminidase.
The bird flu, on the other hand, is also an influenza A virus. But it has the subtype H5N1.
That means that while the human and avian flu virus share the N1 signal, they dont share an H.
If a test is designed to look for only the H1 and H3 as indicators of influenza A virus, theyre going to miss the bird flu.
Marc Johnson, a professor of molecular microbiology and immunology at the University of Missouri, said he doesnt think thats too likely. He said the generic panels that most labs use will capture H1, H3 and H5.
He said while his lab specifically looks for H1 and H3, I think we may be the only ones doing that.
Its been just in the last few years that health officials have started using wastewater as a sentinel for community health.
Alexandria Boehm, professor of civil and environmental engineering at Stanford University and principal investigator and program director for WastewaterSCAN, said wastewater surveillance really got going during the pandemic. Its become a routine way to look for hundreds if not thousands of viruses and other pathogens in municipal wastewater.
Three years or four years ago, no one was doing it, said Boehm, who collaborates with a network of researchers at labs at Stanford, Emory University and Verily, Alphabet Inc.s life sciences research organization. It sort of evolved in response to the pandemic and has continued to evolve.
Since late March, when the bird flu was first reported in Texas dairy cattle, researchers and public health officials have been combing through wastewater samples. Most are using the influenza A tests they had already built into their systems most of which were designed to detect human flu viruses, not bird flu.
On Tuesday, the CDC released its own dashboard showing wastewater sites where it has detected influenza A in the last two weeks.
Displaying a network of more than 650 sites across the nation, there were only three sites in Florida, Illinois and Kansas where levels of influenza A were considered high enough to warrant further agency investigation. There were more than 400 where data were insufficient to allow a determination.
Jonathan Yoder, deputy director of the CDCs Division of Infectious Disease Readiness and Innovation, said those sites were deemed to have insufficient data because testing hasnt been in place long enough, or there may not have been enough positive influenza A samples to include.
Asked if some of the tests being used could miss bird flu because of the way they were designed, he said: We dont have any evidence of that. It does seem like were at at a broad enough level that we dont have any evidence that we would not pick up H5.
He also said the tests were standardized across the network.
Im pretty sure that its the same assay being used at all the sites, he said. Theyre all based on ... what the CDC has published as a clinical assay for for influenza A, so its based on clinical tests.
But there are discrepancies between the CDCs findings and others.
Earlier this week, a team of scientists from Baylor College of Medicine, the University of Texas Health Science Center at Houston, the Texas Epidemic Public Health Institute and the El Paso Water Utility, published a report showing high levels of bird flu from wastewater in nine Texas cities. Their data show that H5N1 is the dominant form of influenza A swirling in these Texas towns wastewater.
But unlike other research teams, including the CDC, they used an agnostic approach known as hybrid-capture sequencing.
So its not just targeting one virus or one of several viruses, as one does with PCR testing, said Eric Boerwinkle, dean of the UTHealth Houston School of Public Health and a member of the Texas team. Were actually in a very complex mixture, which is wastewater, pulling down viruses and sequencing them.
Whats critical here is its very specific to H5N1, he said, noting theyd been doing this kind of testing for approximately two years, and hadnt ever seen H5N1 before the middle of March.
Blake Hanson, an assistant professor at the University of Texas Health Science Center at Houston School of Public Health and a member of the Texas wastewater team, agreed, saying that PCR-based methods are exquisite and highly accurate.
But we have the ability to look at the representation of the entire genome, not just a marker component of it. And so that has allowed us to look at H5N1, differentiate it from some of our seasonal fluids like H1N1 and H3N2, he said. Its what gave us high confidence that it is entirely H5N1, whereas the other papers are using a part of the H5 gene as a marker for H5.
Boerwinkle and Hanson underscored that while they could identify H5N1 in the wastewater, they cannot tell where it came from.
Texas is really a confluence of a couple of different flyways for migratory birds, and Texas is also an agricultural state, despite having quite large cities, Boerwinkle said. Its probably correct that if you had to put your dime and gamble what was happening, its probably coming from not just one source but from multiple sources. We have no reason to think that one source is more likely any one of those things.
But they are pretty confident its not coming from people.
Because we are looking at the entirety of the genome, when we look at the single human H5N1 case, the genomic sequence ... has a hallmark amino acid change ... compared to all of the cattle from that same time point, Hanson said. We do not see that hallmark amino acid present in any of our sequencing data. And weve looked very carefully for that, which gives us some confidence that were not seeing human-human transmission.
The Texas team approach was really exciting, said Devabhaktuni Srikrishna, the CEO and founder of PatientKnowHow.com, noting it exhibited proof of principle for employing this kind of metagenomic testing protocol for wastewater and air.
He said government agencies, private companies and academics have been searching for a reliable way to test for thousands of microscopic organisms such as pathogens quickly, reliably and at low cost.
They showed it can be done, he said.
May 16, 2024 1:09 pm PDT | Updated May 16, 2024 1:58 pm PDT
CALIFORNIA A unusual surge in flu virus detected in California wastewater is raising alarm bells in the Golden State because the flu is not surging. In fact, flu season is in retreat. Bird flu, however, is spreading among dairy cattle nationwide and infected one farm worker earlier this year. Experts worry the viral spike in wastewater means that bird flu could be spreading more widely than is currently understood.
Bird flu, which refers to strains of influenza that spread among birds, has been documented for decades. Outbreaks have decimated populations of wild birds and poultry farms. The viruses can also spread to mammals which is what has been happening recently with the H5N1 strain. Those kinds of mutations pose a greater risk that the virus could spread to humans, experts say.
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"This virus has the potential to seriously disrupt our agricultural supplies and also jump from other mammals to humans and become an epidemic or even a pandemic," Dr. Michele Barry of the Stanford Center for Innovation in Global Health told Stanford Medicine, a university publication.
Millions of poultry birds in 48 states including California have been sickened by H5N1 since 2022. It was first reported in cattle in March. Since then, outbreaks have spread to 46 dairy herds in nine states, according to U.S. Centers for Disease Control and Prevention data.
One farm worker became infected after being exposed to dairy cattle in Texas, the CDC said in April. The worker reported only eye redness as a symptom and has since recovered. Another person was infected with H5N1 in 2022 after being exposed to poultry, the agency said.
Still, the CDC casts the possibility of a human outbreak of H5N1 as unlikely.
CDC believes the current risk of A(H5N1) infection to the general public remains low, the agency said last week.
But some experts have raised concerns that regulators arent watching H5N1 closely enough amid the spread to mammals, which has also proven to be fatal to dozens of other mammal species worldwide, the PBS NewsHour reported.
What we have is a situation where the virus, in a sense, has more shots on goal to jump from a related species, a mammal like us. And now people are no doubt being exposed on a daily basis in pretty large numbers, Michael Worobey, an evolutionary biologist at the University of Arizona told PBS.
Stanfords Barry pointed out that there has been no evidence of human-to-human transmission. But scientists are lacking data in that area: She said in the case of the Texas dairy worker, researchers were unable to do testing that could help reveal how transmissible the virus might be to humans.
Some experts say more attention should be focused on wastewater, which is routinely tested to determine the levels of influenza A viruses in a community. That includes typical flu bugs that spread between people each winter, but it also includes H5N1, the Los Angeles Times reported.
Recent testing has shown a moderate-to-high upward trend in dozens of communities across California, including in the Bay Area and San Diego. Thats unusual for this time of year flu season has ended. The data doesnt necessarily mean that bird flu is present in local wastewater, but it does raise the concern, the Times reported.
And at this point, its not possible to discern whether those pops of influenza A include H5N1. A number of experts are urging authorities to specifically test wastewater for bird flu in order to get a better understanding of the current state of the virus.
We need to track the spread of the virus and its evolution, which isnt getting done well by USDA and CDC, Eric Topol, a professor of molecular medicine at Scripps Research Institute in La Jolla told the Times.
A California Department of Public Health spokesperson told Patch that officials have not recently seen an increase in human cases of influenza A and noted that bird flu has not been detected in dairy cattle, dairy products or humans in California to date.
"CDPH has been working with the Centers for Disease Control and Prevention, and local health departments, to monitor influenza A in wastewater and investigate increasing prevalence in wastewater that is not following human influenza trends. CDPH is working with these groups to investigate these increases, including testing specifically for H5 within wastewater," the spokesperson said.
"Local public health departments continue to review our wastewater data and trends in combination with other human influenza surveillance system data and collaborate with partners to better understand factors that could contribute to increases, such as animal sources located in individual sewer systems (e.g., livestock, wild birds or waste from a milk processing plant)."
The CDC recommends that people use masks and eye protection if they're exposed to animals who are sick or potentially sick with bird flu. They should also avoid eating uncooked or undercooked food products, as well as unpasteurized (raw) milk and cheeses.
Recent FDA testing found traces of the virus in 20 percent of retail milk samples, but authorities say pasteurization kills the virus.
In March 2024, the USDA confirmed that dairy cattle in Texas and Kansas had become infected with a highly pathogenic avian influenza H5N1 strain. Scientists have been monitoring H5N1 infections in wild bird and domesticated poultry populations since the strain popped up in North America in 2021, but they thought that bovines were resistant to influenza A viruses (IAV).
[Cow infection] came as a complete surprise, said Lars Erik Larsen, a veterinary virologist at the University of Copenhagen.
In a preprint posted on bioRxiv, which has not undergone peer review, Larsen and his team measured the distribution of IAV receptors across different cow tissues in search of a mechanistic explanation for how cows contracted the bird flu.1 While their preliminary findings helped explain the symptoms reported in infected cows, they also sparked a new hypothesis on whether cows are potential IAV mixing vessels for the generation of novel flu viruses that could acquire human-to-human transmission.
Wild birds are the natural reservoirs for IAV, but mammalian spillovers into pigs, horses, and humans have occurred.2 For example, the IAV H1N1 and H3N2 subtypes originated in wild birds but evolved to routinely circulate in humans on a seasonal basis. However, the news of the virus spreading between cows came out of left field: Cows experience outbreaks of influenza D viruses, but IAV infections are less common, so scientists did not consider them to be susceptible hosts for H5N1.3
Larsen said that one of the most surprising findings coming from the US reports is that huge amounts of virus are found in the milk, but very little nestles in the respiratory tract. It seems like this virus in bovines behaves completely differently than in other species, said Larsen. These findings suggested that the virus may enter and replicate inside cells housed in the udder, but no one had looked at IAV receptor expression in these tissues.
To transfer their viral genomes, IAV bind to sialic acid (SA) receptors on epithelial cells. One of the main reasons that transmission of IAV from birds to humans is low is that avian viruses prefer to enter cells through the SA-2,3 receptor types, which are highly expressed in birds but less common in humans.4 In order to jump these host barriers and infect humans, avian viruses must evolve to bind to SA-2,6 receptors, the dominant type in humans.
Larsen, whose research primarily focuses on avian and swine influenza viruses, previously measured the expression of these receptors in the pig nasal mucosa using two different plant lectins that bind to either the 2,6 human receptor or the 2,3 avian receptor.5 With tools for making these measurements already in hand, Larsen and his team analyzed the expression of these receptors in cow brain, respiratory tract, and mammary gland tissues that were archived in the freezers in the pathology department of his universitys veterinary school.
Larsen and his team observed high expression of the 2,3 avian receptor in the bovine mammary glands, providing a rationale for why this virus appears to readily replicate in this tissue. That can explain why we find so much virus in the milk, said Larsen. They also found some expression of the avian receptor in the respiratory tract but very little evidence of the receptor in the brain, which matches the minimal respiratory or neurological symptoms observed in infected cows.
When they analyzed the data on the human receptor, the team was surprised to also find high expression in the mammary glands, a finding that brought pigs to mind.
Pigs provide a perfect platform for IAV looking to acquire new hosts. They coexpress both the avian and human receptors in their respiratory tracks. This means that pigs infected with both human and avian flus provide these viruses with a space to mingle and swap genome segments to generate new IAV that the human immune system has never seen before. This happened in 2009 when influenza strains of avian, swine, and human origin infected a pig, underwent genetic reassortment, and created a novel H1N1 strain that kicked off the last swine flu pandemic.6
Although the preliminary evidence from Larsens group provides a mechanistic explanation for why H5N1 is appearing in dairy cattle milk, what worries some scientists is that it also suggests that cows could be a potential mixing vessel for avian and human IAV. Thats just in theory, said Larsen. I dont think that the risk is very high.
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Brian Wasik, a virologist at Cornell University who was not involved in the study, said that he welcomes the preliminary analysis on IAV receptor distribution in bovine mammary tissue, which he noted has been limited in the literature. A rapid dissemination of information about that is always great and open for the community to start building hypotheses of how we understand how influenza is moving in this particular tissue, said Wasik.
With respect to the mixing vessel hypothesis, Wasik said, [They] are good hypotheses and worth discussion and worth setting the framework for future research. My concern, and what I expressed publicly, is that the concern of other people overinterpreting those narrow results and moving clearly beyond the hypothesis framework into something larger.
Unlike a protein receptor, which is transformed from a nucleotide sequence via transcription and translation, SA is carbohydrate that is synthesized by enzymatic processes. There's a lot of heterogeneity and kinetics in that process, and you get lots of different chemical variations of these receptors, said Wasik.
These enzymatic processes lead to different subtypes of the SA-2,6 receptor: the N-Glycolylneuraminic acid (Neu5Gc) and N-Acetylneuraminic acid (Neu5Ac) forms. Neu5Gc is prevalent across different mammals, but the gene that encodes the enzyme that converts Neu5Ac into Neuro5Gc is absent in humans.7 Wasik noted that Sambucus nigra lectin, the molecule used in this study to detect the presence SA-2,6, has a broad binding profile and therefore cannot distinguish between these two subtypes. Therefore, bovine may not express the Neu5Ac form of SA-2,6 that the human influenza strains use to enter cells.
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The methodology needs a lot more rigorous verification, said Wasik, who noted that hed like to see a deeper dive into the chemistry of the bovine receptors to better understand what they look like and how influenza binds to them. Im sure that those studies are coming from this group and a number of others, but at this time we do not have a definitive understanding of what's present in that tissue, he said.
Scientists still need to determine whether cow mammary glands are susceptible to human IAV. More than 70 years ago, researchers injected cow udders with human influenza virus and observed viral replication, suggesting that it is possible.8 However, these were direct injections and it is still unclear if or how human transmission to the mammary glands would occur. Scientists still dont know the mode of transmission of the avian virus into cows.
There are so many unanswered questions about this bovine infection, said Larsen.
In addition to increasing the sample size, Larsen would like to look more closely at the receptor distribution in the respiratory tract. What we fear [is] that this virus starts to spread among cows by droplets because then the risk of human exposure will increase, said Larsen.
Given these are all hypotheses and we don't know what this virus is going to do next, my suggestion is we stamp it out as quickly as possible, said Wasik. While we're concerned about human risk and now this new risk to cattle, what we're seeing is one of the largest ecological die-offs of avian species and sea mammals and a number of other different spillovers.
Texas Techs BTRL confirmed the first human case of HPAI A (H5N1) transmitted from a dairy cow, marking a significant milestone in understanding the viruss transmission and prompting immediate and effective collaboration with the CDC for further research and response.
The Biological Threat Research Laboratory (BTRL) at Texas Tech University was instrumental in identifying the first case of highly pathogenic avian influenza (HPAI) A (H5N1) being transmitted from a mammal (dairy cow) to a human.
The case was made public in an article published in the New England Journal of Medicine. Steve Presley, the director of The Institute of Environmental and Human Health (TIEHH) and the BTRL, and Cynthia Reinoso Webb, the biological threat coordinator at TIEHH, were co-authors on the journal publication.
The journal article explains that in March a farm worker who reported no contact with sick or dead birds, but who was in contact with dairy cattle, began showing symptoms in the eye and samples were collected by the regional health department to test for potential influenza A.
Initial testing of the samples was performed at the BTRL, which is a component of the Centers for Disease Control and Prevention (CDC) Laboratory Response Network-Biological (LRN-B) located at TIEHH.
Its a huge thing that the virus has jumped from birds to mammals, dairy cows in this case, and then to humans, Presley said. Thats why this paper in the New England Journal of Medicine is very significant. Its going to lay the foundation, I believe, for a lot of research in the future of how the virus is evolving.
The involvement of Texas Techs BTRL is a continuation of the partnership between regional, state, and federal public health partners.
Being part of the CDC LRN-B, we have the standing capability to test for a lot of biological threats and some that are considered emergent, Reinoso Webb explained.
The labs standby status allowed Reinoso Webb and the Texas Tech BTRL team to respond quickly to the needs of the regional public health authority. Knowing the potential dangers of the virus, Reinoso Webb pushed the testing into the safest laboratory available, and the team went to work.
Having received the samples in the early evening, results were being reported to regional, state, and federal levels within hours. By the next day, the samples were on their way to the CDC for further testing and confirmation.
We were on the phone with the CDC until around midnight discussing different scenarios and follow-up requirements, Reinoso Webb said. There is a lot of federal reporting. It was a very complicated case, even though it was two samples and one patient.
But we had this wonderful communication with the CDC and made sure we did everything by the book. This is how its been structured, and this is how the communication was supposed to happen.
Reference: Highly Pathogenic Avian Influenza A(H5N1) Virus Infection in a Dairy Farm Worker by Timothy M. Uyeki, Scott Milton, Cherissa Abdul Hamid, Cynthia Reinoso Webb, Steven M. Presley, Varun Shetty, Susan N. Rollo, Diana L. Martinez, Saroj Rai, Emilio R. Gonzales, Krista L. Kniss, Yunho Jang, Julia C. Frederick, Juan A. De La Cruz, Jimma Liddell, Han Di, Marie K. Kirby, John R. Barnes and C. Todd Davis, 2 May 2024, New England Journal of Medicine. DOI: 10.1056/NEJMc2405371
William Brangham:
In fact, unlike cows, this bird flu has been deadly to the nearly two dozen other mammal species that have been infected in this U.S., from a polar bear in Alaska, to a mountain lion in Colorado, to raccoons and foxes. Many of those animals were likely infected by eating dead animals that were carrying the virus.
But, by far, the biggest impact here in the U.S. has been on birds. Since this strain of avian influenza first arrived in the U.S. in early 2022, brought here by migratory birds, more than 90 million domestic birds, mostly chickens and turkeys, have died or been intentionally killed across 48 states.
And unlike previous outbreaks, this variant has affected more wild birds and spread across a wider geographic area, crossing down into South America at the end of 2022.
Dr. Ralph Vanstreels, University of California, Davis: I think the alarm really went off when it reached Peru, and that's a massive seabird community, and we saw just unprecedented mortality in the seabirds there.
