The world is in the grip of a multi-year panzootic the animal equivalent of a pandemic.
Its caused by a lineage of the highly pathogenic avian influenza A (H5N1) virus, or bird flu, clade 2.3.4.4b. It first emerged in Europe in late 2020 and now effects wild birds and poultry in every continent except Australia.
It has also made the jump to mammals in what are known as spillover events. On 25 March US officials reported H5N1 had been detected in cattle for the first time, which has since spread to cows in 36 herds in 9 states.
The US Centers for Disease Control and Prevention issued a health alert on April 1 after a Texas farm worker tested positive for the virus, which he contracted after being exposed to infected dairy cattle.
So, should we be worried about it in Australia?
Strains of avian influenza are either classified as high pathogenicity (HPAI) or low pathogenicity (LPAI) based on their clinical effect.
Most avian influenza viruses are of low pathogenicity and commonly infect wild birds such as waterfowl (Anseriformes) and shorebirds, terns and gulls (Charadriiformes). But when viruses of the A (H5) and A (H7) subtype get into chickens they have the potential to mutate to become highly pathogenic.
In 1997 the HPAI H5N1 virus first emerged in poultry in Hong Kong, and again in China in 2003, and has predominantly remained a disease in chickens since.
Wild birds very, very rarely carry HP virus around because, obviously, being highly pathogenic, its got a significant disease impact to the infected birds, says Dr Frank Wong, a senior research scientist at the CSIROs Australian Centre for Disease Preparedness (ACDP) and the World Organization for Animal Health (WOAH) laboratory reference expert for avian influenza.
This particular lineage [clade 2.3.4.4b] has been quite adaptable and able to infect many species of birds with unpredictable and varying impacts, says Wong.
This means when the virus infects wild migratory waterfowl it might be asymptomatic, and because the birds dont feel sick they are able to carry it over long distances.
But when the virus infects other birds, it could also have quite a devastating impact in that the birds fall sick very rapidly and then you also get mass mortalities, says Wong.
Wong says there is significant concern about the virus impact on poultry production, but also its impact and implications to wildlife populations.
H5N1 now presents an existential threat to the worlds biodiversity, Dr Chris Walzer, Wildlife Conservation Society Executive Director of Health, told Cosmos in March.
It has infected over 150 wild and domestic avian species around the globe as well as a dozens of mammalian species.
Of the current outbreak in the US in dairy cattle, Wong says there is not a lot of evidence to suggest its a respiratory infection, instead the virus is infecting the mammary glands.
Given how dairy farms operate, obviously if theres high virus growth in the milk there is potential for quite substantial environmental contamination. And also, the milking or farming equipment being contaminated and then spreading from herd to herd.
US authorities say that pasteurisation is effective at inactivating HPAI and testing has not detected any live, infectious virus in the commercial milk supply.
Instances of humans contracting the virus from infected animals are rare. According to the World Health Organization, from 2003 to 1 April 2024 there have been a total of 889 cases and 463 deaths a 52% mortality rate reported from 23 countries.
Of these, 13 cases have been associated with clade 2.3.4.4b in 7 countries since January 2022 but no instances of human-to-human transmission have been identified.
Wong says that most of these infected cases in humans have been epidemiologically linked to confirm that they were close contacts of infected animals.
Most of those cases were from those situations where people were dealing with an outbreak in either domestic or wild birds.
Wong adds: The advisory in the US and also in other countries, including Australia, is that when people are dealing with mortality events or a bird flu event, that only authorised persons are dealing with the sick and dead animals and those authorised people should be wearing PPE.
There is no way to prevent the strain from entering Australia through migratory wild birds.
Thus far, Australia has been able to avoid the virus because it is located outside of the migratory flyways of the wild birds that predominantly carry it.
But given that this virus has now infected a very large number of different species to different impacts, there is that potential that there are bridging species that could bring the virus into Australia, says Wong.
For example, Southeast Asia already has this virus its pretty much close to our doorstep.
In December 2023, Australias Chief Vet published an updated incursion risk assessment on the likelihood of entry and establishment of HPAI in Australia via wild birds found that there is: a high risk, with moderate uncertainty.
The authors write: It is expected that the likelihood and associated risk of incursions into Australia will continue to remain at these levels for some time and potentially increase rather than diminish given continued virus evolution.
Relevant agencies are keeping up to date with regional and global circulation of the virus.
There is also a campaign to raise public awareness that unusual events should not be dealt with by members of the public. Instead, they are to be reported immediately so the animals can be properly diagnosed in a nominated state laboratory or the ACDP national reference laboratory.
Wong says that animal health labs have been coordinating with ACDP to ensure their diagnostic tests are able to pick up this lineage with good sensitivity.
There is also a wild bird surveillance program that occurs in Australia, coordinated by Wildlife Health Australia with wild bird faecal sampling to survey for avian influenzas, he says.
Anything that is positive from active surveillance that is detected by the state animal health labs is sent to us as the national reference lab for confirmation and also for full characterisation.
When we do that, were able to tell whether those viruses are local avian influenza viruses that occur naturally in our wild birds, or whether a sample that is picked up as positive was due to an introduced virus.
Key Takeaways
The Food and Drug Administration (FDA) has always advised against drinking raw milk, but the agency is reminding consumers to avoid unpasteurized dairy products because of the current bird flu outbreak in cattle herds.
Clinical samples of raw milk from states including Idaho, Kansas, Michigan, New Mexico, North Carolina, Ohio, South Dakota, and Texas have tested positive for the virus. Multiple domestic cats have died after drinking raw milk and colostrum from infected cows, according to a recent report.
The FDA has found that commercially available milk, cottage cheese, and sour cream contain fragments of the bird flu virus. Although additional testing didnt detect any live, infectious virus in pasteurized products, health experts say to steer clear of raw milk in the meantime.
Raw milk, to me, is a very scary thing. I even recommend those who are feeding milk to their calves to pasteurize it. Its a very known, tested way to enhance food safety and security, Michael D. Kleinhenz, DVM, PhD, a dairy cattle veterinarian and a clinical associate professor at Texas A&M University, told Verywell.
Testing has shown that pasteurization is effective in inactivating the bird flu virus. Pasteurization, which uses high temperatures to kill germs, has significantly reduced infection rates from various diseases since its widespread adoption in the United States during the 1950s.
It remains uncertain if raw milk can transmit the bird flu virus to humans, but unpasteurized milk is known to harbor dangerous pathogens like Salmonella, E. coli, and Listeria.
Its legal to buy raw milk in 27 states, and advocates say its healthier and more nutritious than pasteurized milk. However, theres no strong evidence to support these claims, and pasteurization does not destroy the nutritional value of milk.
Raw milk contributes to hundreds of infections in the U.S. each year. Between 1998 and 2008, more than 2,600 illnesses and 228 hospitalizations were associated with raw milk, according to a study published in the journal Epidemiology and Infection.
I think its a step backward to continue to promote unpasteurized milk. I think the health benefits do not outweigh the disease risk benefits, said Scott R.R. Haskell, DVM, MPVM, PhD, a food safety expert and a professor at the Institute for Food Laws and Regulations at Michigan State University.
Only two cases of bird flu infections in humans have been reported in this outbreak. Infected individuals may have no symptoms or experience mild or severe upper respiratory symptoms, fever, body aches, fatigue, sore throat, nausea, diarrhea, or pink eye.
Both cases involved close animal contact, not consumption of infected food, and the risk of infection for the general public remains low. Haskell said that people dont need to worry about contracting bird flu from eggs, milk, or meat.
Im very concerned about non-pasteurized milk for Salmonella and E. coli. But Im not really that concerned about avian influenza, Haskell said.
The FDA has advised manufacturers against using raw milk from exposed or sick cows for any dairy products. While scientists are still learning if raw milk can transmit bird flu to humans, many experts say it's simply not worth the risk, especially for children and immunocompromised individuals.
Cattle may be infected with avian influenza. And if theyre drinking raw milk, they may be drinking live virus in that milk. They dont have that protection mechanism of pasteurization to inactivate that virus and render it dead essentially, Kleinhenz said.
Many public health agencies recommend avoiding raw milk. It is not clear that raw milk can transmit bird flu, but unpasteurized milk can carry plenty of other germs.
Food and Drug Administration. Questions and answers regarding milk safety during highly pathogenic avian influenza (HPAI) outbreaks.
Burrough ER, Magstadt DR, Petersen B, Timmermans SJ, Gauger PC, Zhang J, et al. Highly pathogenic avian influenza A(H5N1) clade 2.3.4.4b virus infection in domestic dairy cattle and cats, United States, 2024. Emerg Infect Dis. 2024. doi:10.3201/eid3007.240508
Food and Drug Administration. Updates on highly pathogenic avian influenza. (HPAI).
Centers for Disease Control and Prevention. Raw milk questions and answers.
Koski L, Kisselburgh H, Landsman L, et al. Foodborne illness outbreaks linked to unpasteurised milk and relationship to changes in state laws United States, 19982018. Epidemiol Infect. 2022;150:e183. doi:10.1017/S0950268822001649
Centers for Disease Control and Prevention. H5N1 bird flu: current situation summary.
Centers for Disease Control and Prevention. Bird flu virus infections in humans.
Centers for Disease Control and Prevention. Prevention and antiviral treatment of bird flu viruses in people.
By Stephanie Brown Brown is a nutrition writer who received her Didactic Program in Dietetics certification from the University of Tennessee at Knoxville. Previously, she worked as a nutrition educator and culinary instructor in New York City.
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In December, 2021, a few weeks after the Omicron variant emerged to spark a new, punishing phase of the COVID-19 pandemic, Jim Lesters birds got sick. Lester, who owns an exhibition farm in Newfoundland, Canada, learned that the culprit wasnt the novel coronavirus but the first known outbreak in North America of a highly pathogenic strain of bird flu, called H5N1. Hundreds of birds were infected and died. Scores morepeacocks, geese, an emuhad to be culled. They all had personalities, Lester said. It was a true tragedy. Since then, the virus has propagated down through the Americas, killing tens of millions of birds and, perhaps more concerning, infecting dozens of mammalian species: bottlenose dolphins in Florida; sea lions in Peru; elephant seals on the islands near Antarctica. Now, for the first time, the virus is circulating among cattle, and at least thirty-four herds across nine states in this country are known to be infected. Last month, the Food and Drug Administration announced that one in every five samples of milk in the United States carries fragments of the virus, suggesting an even wider spread. One expert called the situation totally unprecedented.
Influenza is a promiscuous pathogen. Its potential to unleash pandemics is due partly to the modular structure of its genome, which allows it to swap segments of its genetic material wholesale when different versions of the virus co-infect a cell. This occurred in the mid-nineties, when H5N1 was first isolated, from a goose in southern China, and went on to infect some twenty per cent of the poultry in Hong Kong markets, precipitating the slaughter of more than a million and a half chickens. In the intervening decades, the virus has periodically caused devastating outbreaks in poultry, but it remains poorly suited to the human respiratory tract, and that has limited its spread among people. Still, for those who do get infectedusually farmworkers and others with exposure to animalsthe effects can be lethal. In some prior outbreaks, the virus inflicted a case-fatality rate of more than fifty per cent. Fortunately, only two people in the U.S. are known to have been infected, and both experienced mild symptoms. Since 2022, only about two dozen human cases have been recorded worldwide, and, according to the Centers for Disease Control and Prevention, the risk to public health remains low.
The prevalence of the virus in our milk supply may also be less alarming than it sounds. The P.C.R. test used to identify it can detect minuscule amounts of genetic debris, and a positive result does not imply that the virus is alive, much less contagious. Nearly all milk sold in the U.S. is pasteurizedheated to destroy potential pathogensand that process may be especially effective for unstable viruses such as influenza. (Many statessome, recently, as part of a broader backlash against public-health measureshave legalized the sale of raw milk, which health officials generally do not advise consuming.) The tests needed to conclusively determine whether pasteurization kills H5N1 take time and involve injecting eggs with milk samples, but, according to the F.D.A., preliminary studies havent found any traces of live virus.
It now seems likely that H5N1 was first transmitted from a bird to a cow late last year, and that the virus has been circulating unchecked among cattle for months. Many cows who shed the virus dont show symptoms, and how it spreads among them remains a mystery. Contamination of milking equipment is the most probable route, but respiratory transmission is also a possibility. So far, pigs havent contracted the virus, which is good for themand us. Pigs have receptors for both avian and human versions of the flu, so they can serve as mixing vessels, facilitating genetic exchange in ways that could spawn a mutant capable of spreading among people and igniting another pandemic.
In the unlikely event of that emergency, were far better positioned than we were for COVID. Influenza may be the worlds most familiar viral pathogenits genome, virulence, and transmission patterns have been studied for decades. The U.S. has a large stockpile of Tamiflu, which should work against bird flu, as it does for other influenza strains, and which could be given to an infected persons contacts to mitigate spread. Health officials have also indicated that they could rapidly scale up testing and, if needed, shift the nations annual flu-vaccine production to shots that are tailored for H5N1.
But the ability to respond is not the same as responding. The countrys initial approach has had an unsettling resonance with the first months of COVID. Because there is no widespread program to screen farm animals for H5N1, we have little sense of how many have been tested or what proportion of tests have been positive. It took a month after bird flu was detected in cattle for the Department of Agriculture to require that lactating cows be tested before crossing state lines, and the agency has since clarified that only thirty animals in a group must be tested, irrespective of how large the group is. Last month, when the government released genetic sequences for scientists to study, it did not share information about where or when the samples were collected, making it difficult to track how the virus is spreading and evolving. Meanwhile, we havent conducted antibody studies of farmworkers that could determine the extent to which they are getting infected; well know theyre sick if they show up in emergency rooms.
Many hospitals, of course, are still reeling from the pandemic, and leaders have expressed concern that they dont have the staffing, the resources, or the morale to contend with another crisis. The deeper problem, though, is the countrys COVID hangover. America has emerged from the pandemic not just fatigued, but resentful and divided. If bird flu becomes human flu, one gets the sense that our principal fight wont be with the virus, but with one another.
In Albert Camuss novel The Plague, the vectors of disease are not birds but rats. The authorities are slow to act and, as the death toll mounts, people grow depressed, distrustful, violent. Even when the crisis eventually recedes, a doctor comes to feel that plague never dies or disappears for good. He notes, Perhaps the day would come when, for the bane and the enlightening of men, it would rouse up its rats again and send them forth to die in a happy city. The rise of pandemic pathogens is an inextricable part of the modern world. The scale of their destruction doesnt have to be.
The Texas dairy worker who caught bird flu from a sick cow in late March had none of the symptoms typically associated with influenza, including fever, coughing or sneezing. The only indication that he had been infected was a striking case of pinkeye.
Details of the mans case the only documented instance of bird flu spreading from a cow to a human were published Friday in the New England Journal of Medicine, from health officials in Texas and the Centers for Disease Control and Prevention.
Bird flu was first detected in several herds of dairy cows in late March. Around that same time, the man's right eye started to bother him and became red. He ended up with broken blood vessels in both eyes. Doctors said he had conjunctivitis, or pinkeye. The man had been in direct contact with both healthy and sick cows.
Swabs of the mans eye and nose revealed he had the same strain of bird flu, H5N1, that was circulating in dairy cows.
The man was given the antiviral Tamiflu and was told to isolate as he recovered. No one he lives with became sick, though they, too, were given the antiviral to reduce that risk, the authors wrote.
He never developed respiratory symptoms, which suggests that the virus may not spread easily from person to person through coughs or sneezes.
Indeed, genetic tests done on samples taken from the mans eyes and nose confirmed that there were no mutations that would allow the virus to spread this way.
But the threat that mutations like that could arise is real, especially as the virus continues to spread among dairy cows. As of Friday, 36 herds in nine states Colorado, Idaho, Kansas, Michigan, New Mexico, North Carolina, South Dakota, Ohio and Texas had been affected by the outbreak.
H5N1 viruses pose pandemic potential and have caused severe respiratory disease in infected humans worldwide, the reports authors wrote. Therefore, rapid implementation of preventive measures is recommended to reduce human exposures to any infected animals and environments contaminated by them.
Data from other countries show the virus can have a fatality rate of more than 50% in humans, according to the CDC.
More than 100 people have been told to monitor themselves for symptoms, and about 25 people have been tested for bird flu, the CDC said during a media briefing on Wednesday. So far no one else has tested positive. But veterinary experts suspect that cases are going undetected among dairy farmers worried that theyll lose their cattle if they report a positive test.
Farmers are very, very concerned about what happens if theyre positive, said Dr. Keith Poulsen, director of the Wisconsin Veterinary Diagnostic Laboratory. When I talk to dairy farmers in Wisconsin, a lot of them just want it to go away like, well, what do we do about it? Im really only concerned about whether or not I can make my mortgage next week.
No bird flu has been found in cows in Wisconsin, but Poulsen said the outbreak has the potential to lower consumer confidence about the safety of dairy products.
If the dairy industry takes a hit anywhere in the country, then it takes a hit on us, too, he said. The Department of Agriculture said earlier this week that tests on hundreds of pasteurized products like milk, cottage cheese and sour cream, showed no signs of live virus and are safe to consume.
While the authors of the new report could not rule out the possibility that the Texas dairy worker was infected through respiratory droplets, they wrote that the man likely got infected by rubbing his eyes with a contaminated hand. He was wearing gloves but no goggles or other form of eye protection.
The CDC recommends that anyone in contact with dairy cattle wear protective equipment, including safety glasses, waterproof aprons and boots that can be sanitized.
The authors of the report said they were not able to follow up with the worker to do additional testing to study his antibodies or see how long the virus stayed in his system.
Erika Edwards is a health and medical news writer and reporter for NBC News and "TODAY."
Scientists from the Centers for Disease Control and Prevention (CDC) and their collaborators in Texas today shared new details about an investigation into a recently reported H5N1 avian flu infection in a dairy workerlikely the first known transmission of the virus between mammals and a human.
The team detailed their clinical and genetic sequencing findings today in a letter to the New England Journal of Medicine. The man's infection, which was mild and consisted of conjunctivitis, was first reported on April 1, and the CDC shared its initial sequencing findings the following day.
The man's right-eye conjunctivitis began in late March. He didn't have contact with sick or dead birds or other animals but did have direct contact with healthy dairy cows, as well as ones that had illness signs that were similar to those at nearby facilities where H5N1 was confirmed. He said he wore gloves while working, but not respiratory or eye protection.
Researchers said the man's eyes could have become infected by touching them with virus-contaminated hands, or from exposure to respiratory droplets or aerosols from sick cows or activities in the dairy setting.
Health workers collected nasopharyngeal and conjunctival swabs, which were positive for H5N1 via PCR testing. There was enough RNA in the conjunctival sample for full genome sequencing, and scientists were able to grow the virus from both specimens.
The patient also developed redness in his left eye. He and his household contacts received oseltamivir (Tamiflu), and over the following days, the man recovered, and no symptoms were reported in his contacts.
We were also unable to collect acute or convalescent sera to assess seroconversion in the dairy farm worker or household contacts.
In the supplementary appendix, researchers said they weren't able to do a follow-up investigation on the sick worker or other exposures among workers at the farm. They also noted that they weren't able to collect follow-up specimens from the patient to track viral loads or shedding duration. "We were also unable to collect acute or convalescent sera to assess seroconversion in the dairy farm worker or household contacts," the group wrote.
A spokesperson for the Texas Department of State Health Services told CBS News that the Texas dairy worker came to a Texas field office for testing and did not disclose the name of his workplace.
Initial sequencing found that the virus belonged to the same B3.13 genotype circulating in dairy cows, and virus isolation from both specimens yielded identical viruses. As reported earlier by the CDC, the virus in the man's specimen had a change, PB2 E67K, that has a known link to virus adaptation to mammalian hosts.
In the supplementary appendix, the group said when they compared the sequence from the patient with the available cattle sequences, they found that the human sequence lies just outside the larger cluster of cattle sequences from Texas, though it is closer to cattle than B3.13 genotype viruses from wild birds or wild mammals.
"Sequence data from the farm where the infected dairy farm worker was exposed to presumably infected was not available," they wrote, noting that the sequencing picture so far has gaps and suggests the virus may have been circulating undetected for some time.
They said it's possible that the patient was infected with an earlier slightly different virus or that there was more than one independent spillover of the B3.13 genotype from wild birds to cattle.
Taken together, though, they wrote the genetic and epidemiologic evidence provide strong evidence of transmission from a sick cow to a human.
The H5N1 virus infecting dairy cattle in multiple states was probably circulating in the animals for 4 months before scientists confirmed it in late March, and missing data and surveillance gaps raise the possibility of undetected transmission chains, a research team led by the US Department of Agriculture (USDA) National Veterinary Services Laboratory (NVSL) reported in a new preprint study.
In the first published report that interlaces genetic sequencing findings with what's known from the epidemiological investigation, the group said asymptomatic cattle movement to other states is likely driving transmission and that they are already seeing a few variants with mutations that could lead to interspecies transmission. The group published their findings yesterday on the preprint serverbioRxiv.
In other H5N1 developments, the USDA last night announced that its tests on retail ground beef from affected states were negative, and two affected statesMichigan and Coloradoannounced new emergency measures.
Phylogenetic analysis using genome sequencing suggests that there was a reassortment event in late 2023 between the current highly pathogenic 2.3.4.4b clade in wild birds and a low-pathogenic wild bird strain, which produced the B3.13 genotype now circulating in dairy cows.
The NP gene acquired during reassortment may have played a role in the emergence in cattle, they wrote, noting that the NP gene seems to allow influenza viruses to spread more easily in pigs.
Their analysis suggests there were as many as five B3.13 introductions from cattle to poultry, one to a raccoon, two to domestic cats, and three to wild birds. Though the findings track with epidemiological findings of spread through movement of herds to other states, they emphasized that there are still gaps. "We cannot exclude the possibility that this genotype is circulating in unsampled locations and hosts as the existing analysis suggests that data are missing and under surveillance may obscure transmission inferred using phylogenetic methods," they wrote.
For example, they said the B3.13 virus from the human infection doesn't nest within cattle sequences, which could suggest that viruses from unsampled cows were the source of the infection or that evolution within the host was enough to result in a different phylogenetic grouping. "It is most likely, however, that asymptomatic transmission and undersurveillance in epidemiologically important populations drove this pattern."
They conclude that the potential for B3.13 to become endemic in cattle will influence the zoonotic risk from the virus and warned that if the low level of mammalian adaptations they're seeing become dominant, the risk of interspecies transmission will be higher.
After the group published its report, Angela Rasmussen, PhD, a virologist with the University of Saskatchewan's Vaccine and Infectious Disease Organization,on X (formerly known as Twitter), praised the group for sharing the critical data.
However, she said more information is needed, such as the tissue and or sample type each genome came from, which is essential for understanding how cows are transmitting the virus and planning experiments to test transmission hypotheses. "This is an all-hands situation and transparency & data access are required for an effective response," Rasmussen wrote.
Michael Osterholm, PhD, MPH, who directs the Center for Infectious Disease Research and Policy (CIDRAP) at the University of Minnesota, publisher of CIDRAP News, also credited the USDA group for sharing their findings and said the science community has been anxiously waiting for the critical information.
"This will help people better understand how the spillover unfolded," he said.
In its update, the USDA said it tested 30 samples of retail ground beef from states where dairy herds tested positive for H5N1. The samples underwent polymerase chain reaction (PCR) testing, which can identify traces of the virus but not live virus, at the NVSL. All were negative.
"These results reaffirm that the meat supply is safe," the agency said.
The USDA added that PCR testing is under way on muscle samples from culled dairy cows at selected USDA Food Safety and Inspection Service (FSIS) slaughter facilities and that its Agricultural Research Service is conducting a cooking study using a virus surrogate in ground beef to examine the impact of different cooking temperatures on virus levels.
Two states affected by H5N1 outbreaks in dairy herds yesterday announced emergency measures aimed at controlling the spread of the virus.
In Michigan, where recent outbreaks in dairy cows and massive outbreaks in poultry were reported across seven counties, the Department of Agriculture and Rural Development (MDARD)announced an extraordinary emergency measure that requires dairy farms and commercial poultry farms to implement biosecurity steps such as designating a biosecurity manager, establish cleaning procedures, and keeping a log book of vehicles and people who have crossed farm-access points.
The order also bars all lactating cattle from being displayed until the state has passed 60 days with no new dairy farm detections. Officials also announced a similar restriction for poultry, but for 30 days with no new detections.
Elsewhere, Colorado's agricultural commission approved, and the state's agriculture commissioner yesterday adopted, an emergency rule designed to limit the spread of H5N1. Colorado is the most recently affected state in the outbreak involving dairy cattle, and so far, it's not clear how the cows were exposed to the virus.
In itsannouncement, the Colorado Department of Agriculture said the emergency rule requires mandatory testing of lactating cattle moving interstate, which they said allows implementation of the recent federal order, which took effect on April 29.
BANBURY, UNITED KINGDOM: A man in a protective body suit walks past a sign warning of a outbreak of ... [+] the H7 strain of bird flu. (Photo by Matt Cardy/Getty Images)
The U.S. Centers for Disease Control and Prevention notified the public in early April that an individual in Texas had tested positive for highly pathogenic avian influenza, or bird flu. This persons only symptom was conjunctivitisor redness of the eyesafter being exposed to dairy cattle that were presumed to be infected with HPAI. This was the second documented human case of avian influenza in the United States since 2022 and has escalated concerns about a large outbreakor potentially a pandemicin the human population.
Influenza viruses, which cause annual epidemics of mild to severe respiratory illness, are not unique to humans. Certain subtypes of influenza circulate among animals, including birds, swine, horses, dogs and bats. Infection in some animals, such as wild waterfowl, may be asymptomatic (i.e., no disease results from the infection) and these animals are considered a natural reservoir for the virus. However, transmission of the virus to other animals, such as backyard bird flocks or commercial poultry, may have devastating consequences.
Since January of 2022, the largest outbreak of avian influenza in recorded history has occurred worldwide. To date, a subtype of highly pathogenic avian influenzaknown as H5N1has been detected in over 9,000 wild birds and has affected greater than 90 million poultry in the United States. Recently, the virus has been identified in certain mammals, including dairy cattle, prompting concern that it may be adapting for more efficient transmission among mammalian species. Although sequencing studies have not yet demonstrated this to be the case, the recent human case in Texas has some asking, Could avian influenza result in the next pandemic?
A highly pathogenic subtype of avian influenza, known as H5N1, has affected greater than 90 million ... [+] poultry in the United States.
In early 2020, a novel virusnow known as SARS-CoV-2began circulating across the globe. The human population had no prior immunity to this virus, no vaccines or treatments existed, and there was limited understanding of how the virus was transmitted and the mechanisms by which it caused disease. These factors contributed to the Covid-19 pandemic, which resulted in over 700 million cases and 7 million deaths worldwide. Although HPAI has the potential to cause a significant outbreak in the human population, there are several significant differences of HPAI that make a global pandemic on the scale of Covid-19 less likely.
The highly pathogenic avian influenza subtype H5N1 was first identified in Southern China in 1996 during an outbreak in domestic waterfowl, and it resulted in more than 850 human infections with a mortality rate greater than 50%. Since then, this influenza virus, as well as other low- and high-pathogenic subtypes, have caused outbreaks among animals, and less frequently, in humans. This has allowed researchers, infectious diseases specialists and public health officials to study these viruses and gain valuable insights into their transmission, pathogenicity and potential treatments.
One of the most significant challenges during the early weeks of the Covid-19 pandemic was we had no way to identify who was infected. This allowed for cases to go undiagnosed and fueled the spread of the virus. In contrast, some tests that we currently use to diagnose human influenzaespecially molecular tests (e.g., PCR)will detect avian influenza strains, including H5N1. However, most are not able to subtype the virus. In other words, existing flu tests can tell us we are infected with an influenza virus, but theyre not able to differentiate a common human subtype, like H3N2, from an avian subtype, like H5N1. Partnerships are currently underway to develop tests that are specific for highly pathogenic avian influenza strains.
Since we have known about HPAI for nearly three decades, this has allowed researchers time to investigate and develop tools for prevention and treatment. A candidate vaccine against H5N1 exists, and studies have shown that it should elicit a robust immune response against the currently circulating subtype of avian influenza. The CDC has shared it with vaccine manufacturers, so production and deployment could take place rapidly, if needed. In addition, there are multiple FDA-approved antiviral medications used to treat human influenza, and data suggest these treatments are also effective against HPAI. These existing antivirals would help reduce the incidence of severe HPAI cases as well as death.
Although the current risk of a human outbreak of HPAI is low, there are still several steps you can take. First, avoid contact with animals, especially birds or cattle, that are sick or have died. If you must come into contact with these animals, wear eye protection, an N95 respirator and gloves. And finally, get tested for influenza and notify your local or state public health officials if you develop any symptomsincluding a sore throat, cough, fever, body aches or conjunctivitisafter being exposed to an animal that might have HPAI.
A global bird flu outbreak infecting record numbers of chickens and wild birds as well as dairy cows, cattle, and other mammals is raising concerns about whether the influenza A/H5N1 variant circulating right now might become a significant risk to humans.
Another worry is whether eggs and milk are currently safe to consume given the number of affected animals.
[1]Every state has found cases in wild birds, and all but three had outbreaks in poultry.
[2]A variety of animals have been infected, including skunks, bobcats, foxes, raccoons, mountain lions, bears, possums, dolphins, seals, and coyotes.
[3]The infected person was a worker at a commercial dairy farm in Texas who developed conjunctivitis (pink eye) in response to the virus. It also appears to be the first human infection with A(H5N1) acquired from contact with an infected mammal, the WHO said.
Right now the danger to the general public is minimal, according to the WHO. Even for people who work with birds or mammals that can carry these infections, WHO said the risk remains low to moderate.
But experts say worries about the threat of bird flu to humans and a potential pandemic are justified.
Here, Richard Webby, PhD, an infectious disease researcher at St. Jude Graduate School of Biomedical Sciences in Memphis, Tennessee, and the director of the WHO Collaborating Center for Studies on the Ecology of Influenza in Animals and Birds, answers the most pressing questions on bird flu.
Everyday Health: What is bird flu, and how is it different from other kinds of flu?
Dr. Richard Webby: Bird flu is a terrible term. Essentially it encompasses a wide variety of different influenza viruses. In the current situation the best way to help people think about this is to think about COVID-19 with many variants. Influenza also has a range of different variants. The main types that cause seasonal flu in people in the United States are limited to four variants. For avian flu, there are 16 variants in birds. What we have right now [in the current outbreak] is one of those avian flu variants, the H5 virus.
EH: Why are so many birds and mammals getting bird flu?
RW: The problem with H5 is that it has become very adept at infecting migrating birds like ducks. When birds move they bring the virus with them and they spread it to other bird species. Birds of prey like eagles or raptors are probably getting it from eating sick ducks. We are seeing mammals like foxes or skunks getting it, and they are scavenging and probably getting it from feeding on carcasses of infected birds.
We have also now seen cows infected. It is a little unclear how this happened, and infection of this host is a bit of a surprise. It does look like a bird virus somehow infected a cow, and we are now seeing cow-to-cow spread.
EH: Can people get bird flu?
RW: This virus does have the potential to transform from a bird virus to a human virus, but it seems right now to be very difficult for this particular H5 virus to jump to humans; the virus maintains all the characteristics of a virus that will stay within birds. But the risk is not zero, and people have been infected, including one worker on an infected dairy cow farm.
EH: What happens to people who get bird flu? Can they get very sick or die?
RW: We have seen H5 for 25 years, and in all this time we have seen hundreds of people get infected. We havent ever seen it move from human to human.
The human fatality rate is running at about 50 percent, but we have to take this number with a little bit of a grain of salt because we are only detecting people who get really sick and see a doctor. The virus is probably infecting more people who dont get sick, who get infected and are asymptomatic. The most recent case of the dairy cow worker resulted in conjunctivitis and not respiratory disease.
What we do know about this virus is that it has a bigger potential risk for severe disease than seasonal flu because the infection can go deeper down into the lungs.
EH: Are there certain people who are more likely to get bird flu?
RW: Anything you do that increases the risk of coming into contact with an infected bird could increase your risk. Over the past 25 years, most cases in humans have been in countries like China and Egypt, where many people keep birds and there are large poultry markets. Coming in contact with live or sick birds is the highest risk. In the current environment with ongoing cow infections, being in close contact with these animals also increases risk.
EH: Can you talk about bird flu symptoms, diagnosis, and treatment in humans?
RW: Symptoms of bird flu can be similar to seasonal flu symptoms, and you can get tested. Theres a generic test for flu, and if somebody has bird flu this would be positive. Then if its positive, there is a separate test for H5 that can detect bird flu. If people have flu-like symptoms and have been in contact with poultry or bird populations or infected cows, that elevates the possibility that it might be bird flu.
Two drugs that work for seasonal flu can also work for bird flu baloxavir (Xofluza) and oseltamivir (Tamiflu). The key is getting people treated early. The sooner people get treated, the better these drugs will work.
EH: What can people do to prevent catching bird flu? Is there a vaccine?
RW: There is a licensed H5 vaccine in the United States, but its not for this particular version of H5 in circulation right now. It would probably provide some protection against what were seeing right now, though. The United States has some stockpiles of some H5 vaccines, and manufacturers know how to make it. But people cant get a vaccine right now. Its all being held within national stockpiles.
EH: How worried should I be about bird flu in chickens and cows in terms of my food choices do I need to be worried about eating eggs, drinking milk, or eating beef or chicken?
RW: Right now the biggest concern is drinking unpasteurized milk. We know that there are very large amounts of virus in the milk of infected dairy cows and drinking this milk is very risky.
There have been efforts to look for infectious virus in pasteurized milk and beef, which have all, luckily, turned up negative. There is little risk in consuming these products.
Similarly, eggs are not thought to be of concern. Infected chickens are rapidly removed or die, and the chances of an egg from an infected bird entering the food chain is essentially zero.
EH: What about my cat and my dog can they get bird flu?
RW: If theyre running around in the neighborhood and see a dead bird they chew on, there is a risk. Similarly, we have seen cats that have consumed infected milk from the cow dairy farms and have also contracted the disease. Big cats in the zoo do catch it; its not like household cats and dogs are immune. We havent seen any evidence of infected cats or dogs passing it to their owners.
EH: Big picture: How worried should people be about bird flu right now? Is this the next pandemic?
RW: Its really difficult to put this into context. Right now, this is a virus that for a human is very, very difficult to catch.
But if theres a flu virus I wouldnt want to catch its this virus. Weve been following it for 25 years and it hasnt become widespread in humans. But we havent seen it in South America before [it has been identified in animals there recently] and weve seen it only transiently in the United States in the past.
The risk may be very low for humans right now, but the relative risk is as high now as it has ever been. We know influenza viruses can make this jump from an animal virus to humans. Other types of bird flu H1, H2, and H3 have successfully made the leap.
With the history of knowing that flu viruses can do this, there is absolutely the worry about this becoming a pandemic. There are 16 types of flu in birds and only three have successfully made it to humans. Some people read this as the other 13 types probably dont have the capacity to move to humans. I think they still have the potential to do this, but they dont do it easily, and its a much lower risk. Its just not zero.
The U.S. Department of Agriculture is ordering dairy producers to test cows that produce milk for infections from highly pathogenic avian influenza (HPAI H5N1) before the animals are transported to a different state following the discovery of the virus in samples of pasteurized milk taken by the Food and Drug Administration. Justin Sullivan/Getty Images hide caption
The U.S. Department of Agriculture is ordering dairy producers to test cows that produce milk for infections from highly pathogenic avian influenza (HPAI H5N1) before the animals are transported to a different state following the discovery of the virus in samples of pasteurized milk taken by the Food and Drug Administration.
Officially, there is only one documented case of bird flu spilling over from cows into humans during the current U.S. outbreak.
But epidemiologist Gregory Gray suspects the true number is higher, based on what he heard from veterinarians, farm owners and the workers themselves as the virus hit their herds in his state.
"We know that some of the workers sought medical care for influenza-like illness and conjunctivitis at the same time the H5N1 was ravaging the dairy farms," says Gray, an infectious disease epidemiologist at the University of Texas Medical Branch in Galveston.
"I don't have a way to measure that, but it seems biologically quite plausible that they too, are suffering from the virus," he says.
Gray has spent decades studying respiratory infections in people who work with animals, including dairy cattle. He points out that "clustering of flu-like illness and conjunctivitis" has been documented with previous outbreaks involving bird flu strains that are lethal for poultry like this current one.
Luckily, genetic sequencing of the virus doesn't indicate it has evolved to easily spread among humans.
Still, epidemiologists say it's critical to track any possible cases. They're concerned some human infections could be flying under the radar, especially if they are mild and transient as was seen in the Texas dairy worker who caught the virus.
"I think based on how many documented cases in cows there are, probably some decent human exposure is occurring," says Dr. Andrew Bowman, associate professor of veterinary preventive medicine at The Ohio State University. "We just don't really know."
There have been 36 herds affected in nine states. Local and state health departments have tested about 25 people for the virus and monitored over 100 for symptoms, federal health officials said at a briefing on Wednesday.
These people are in "the footprints of where the bovine detections are," says Dr. Demetre Daskalakis, who's with the Centers for Disease Control and Prevention, although he didn't provide details on the actual locations.
"There's a very low threshold for individuals to get tested," he adds.
The lack of testing early in the outbreak isn't necessarily surprising. In places like Texas and Kansas, veterinarians weren't thinking about bird flu when illnesses first cropped up in early March and it took time to identify the virus as the culprit.
But the total number of tests done on humans at this point seems low to Jessica Leibler, an environmental epidemiologist at Boston University School of Public Health.
"If the idea was to try to identify where there was spillover from these facilities to human populations, you'd want to try to test as many workers as possible," says Leibler, who has studied the risk of novel zoonotic influenza and animal agriculture.
Also, notes Gray, the virus is probably much more geographically widespread in cattle than the reported cases show, "possibly spilling over much more to humans than we knew, or then we know."
The federal government has been quick to assess the safety of the dairy supply. On Wednesday, the Food and Drug Administration released findings, showing that infectious virus wasn't present in about 200 samples collected from dairy products around the country. Initial results on ground meat are also reassuring.
However, there still remain "serious gaps" in public health officials' ability to detect bird flu among those who work with cows, a task made all the more difficult by the fact that some cases may not be symptomatic, says Leibler. "There's really widespread opportunity for worker exposure to this virus."
Only complicating matters the true scale of the outbreak in cattle remains murky, although new federal testing requirements for moving cattle between states may help fill out the picture.
"Some of the dairy herds seem to have clinically normal animals, but potentially infected and [that] makes it really hard to know where to do surveillance," says Bowman.
The health care system would likely catch any alarming rise in human cases of bird flu, according to modeling done by the CDC.
Federal health officials monitor influenza activity in emergency departments and hospitals. Hundreds of clinical laboratories that run tests are tasked with reporting findings. And in early April, a CDC health alert was sent to clinicians advising them to be on the lookout for anyone with flu-like symptoms or conjunctivitis who'd worked with livestock.
But even these safeguards may not be sufficient to get ahead of an outbreak.
"I worry a bit that if we wait until we see a spike in those systems that perhaps we would already be seeing much more widespread community transmission," says Dr. Mary-Margaret Fill, deputy state epidemiologist for the Tennessee Department of Health. Instead she says there should be proactive testing.
Fill notes there are anecdotes about farmworkers with mild illness while working with cattle in some of the areas where the virus has spread and "not enough visibility on the testing that's happening or not happening in those populations to understand what might be going on."
To get ahead of the virus, Leibler says not only do workers need to be screened but also their family members and others in the community, in the event that the virus does evolve to spread easily among humans.
Dr. Rodney Young says doctors in the Texas panhandle have been vigilant about any cases of influenza, particularly among those who are around livestock, but so far there are no indications of anything out of the ordinary.
"We just haven't seen people who fit that description in order to suddenly be testing a lot more," says Young,regional chair of the Department of Family and Community Medicine at the Texas Tech Health Sciences Center School of Medicine in Amarillo.
Gray says it can be hard to detect and measure the illness in these rural workers for many reasons their remote location, a reluctance to seek out health care, a lack of health insurance, concerns about immigration status, and a reticence among farmers "to wave the flag" that there are infections.
The farms he works with consider protecting workers and curbing the spread of this virus "a huge priority," but right now they bear all the risks of going public, he says.
Dr. Fred Gingrich says this is a major barrier to closer cooperation between federal health officials and the industry during the current crisis.
Dairy cattle farmers currently don't get compensated for reporting infections in their herds unlike poultry farmers who receive indemnity payments for losses related to culling birds when they find cases, says Gingrich, executive director of the American Association of Bovine Practitioners.
"So what is their incentive to report?" he says, "It's the same virus. It just doesn't kill our cows."
Gray has managed to start collecting samples from humans and cattle at several dairy farms that recently dealt with the virus. It's part of a study that he launched before the H5N1 outbreak in response to concerns about SARS-CoV-2 spillover on farms.
They'll look for evidence of exposure to novel influenza, including bird flu --something he's able to pull off because of his background in this area and his guarantee that the farms will be kept anonymous in the published work.
What concerns him most is the possibility the outbreak could wind up at another kind of farm.
"We know when it hits the poultry farms because the birds die, but the pigs may or may not manifest severe illness," he says, "The virus can just churn, make many copies of itself and the probability of spilling over to those workers is much greater."
Vivien Dugan isnt getting much sleep these days.
The director of the influenza division at the Centers for Disease Control and Prevention, Dugan is leading the team of CDC scientists that is working with partners in the U.S. Department of Agriculture, the Food and Drug Administration, and state and local health departments to respond to the H5N1 bird flu outbreak in dairy cattle.
The response has been pedal to the metal since the USDA announced on March 25 that a strange illness that had been affecting milk production in some herds since early this year was caused by bird flu. Since then, 36 herds in nine states have tested positive for the virus.
Assessing the risk from the situation and messaging it to the public is a balancing act, she admitted. While workers on affected dairy farms are being exposed to the virus one has tested positive so far for the individual American elsewhere, the risk is low, for the moment. Demetre Daskalakis, director of CDCs National Center for Immunization and Respiratory Diseases in which the flu division is housed said Wednesday that 25 people have been tested for H5N1 in the context of this outbreak, and over 100 people have been monitored for symptoms because they were believed to have been exposed.
The responding agencies have long experience working with poultry farmers, whove been plagued by this virus for the past couple of years. But its move into cattle has been like crossing into a new country for the agencies. Dairy farmers have no experience with bird flu. Many farmers and farm workers havent been eager to cooperate with authorities.
In an ideal world, blood samples from people who had contact with the infected farm worker would have been studied to look for H5N1 antibodies to see if he transmitted the virus to anyone, a technique called a serology study. But Dugan said she believes that the people involved wouldnt grant permission. STAT asked Dugan about the work the CDC is doing, the complaints from scientists globally about the amount of information the United States has been sharing, and where the needle on her H5N1 risk meter sits right now. As we spoke, a colorful statue of a rooster was visible on a credenza behind her apt decor for a flu researcher.
The interview has been edited for length and clarity.
The numbers of people tested and/or monitored seems to be implausibly low, given the numbers of workers who would have been exposed to the infected animals. How hard is the U.S. looking for cases?
We had a team pretty much ready to go six weeks ago, when this first really started to show up on our radar. But this is not the average poultry-worker response situation. These are dairy farms. The poultry space and poultry industry, theyve been responding to H5 for the past 2 years, really. Thereve been more than 8,000 people that have been monitored for symptoms in the H5 poultry space. Its a different environment altogether when were talking about dairy cattle and dairy farms.
That said, we are really thinking about how we would go about doing the investigation we would normally do for a novel flu case where theyre all nationally notifiable infections in people in a way that makes scientific and epidemiological sense.
The states are really focusing on that, really trying to get as much information as they can. So its really more in that local space. Were supporting them in that effort. Some states have been able to contact workers directly and actively monitor. Others, of course, have not been as successful.
So its a work in progress. We have a couple of potential locations that were trying to do more with in getting the logistics sorted out. But no studies have been completed yet.
No studies have been completed yet. Have any studies started?
Thats probably a good question for some of the impacted states. We dont want to get ahead of them for any work they may be doing that we dont have all the details on.
It sounds like your team that was ready to go didnt go. And it sounds like from what youre telling me that CDC is very much in the back seat on this one. That its the states or local authorities who are running this.
They have the authority, right? CDC does not have the authority to go into a state. We have to have an invite from state public health.
Have any states invited CDC in?
No. Not officially yet. Were speaking to these partners if not once a day, more than that.
There are a lot of sensitivities. There are a lot of things that we as public health officials may not be aware of in thinking about dairy farms. Were used to working with poultry farms and poultry workers where theyre culling all the birds. These cows are not being culled. So its a very different space.
Were working very closely with the state public health partners, where potentially they might be a lead of a study. And we would be in the background supporting. Sometimes we dont need to deploy a team, we can equip our state public health partners to do the information gathering and work collaboratively with them to do that.
There has been a single human case in Texas. Has anybody done serology testing around that individual? That would be an obvious place to start, would it not?
I dont know that that was consented to. You have to have consent from people to follow up. Certainly it was something that was on our radar for what we would like to have and request, but to my knowledge, serology was not performed. (A report on the case published Friday in the New England Journal of Medicine confirmed Dugans belief. The infected person and his contacts would not consent to have blood drawn.)
The scientific world has been watching H5 for a long time. CDC has been very involved in that. And whenever there have been unusual outbreaks, this country has always pushed for rapid case finding and data sharing.
Im hearing from people outside the United States that when the shoe is on the other foot, when the outbreak is here, theyre not seeing the information sharing that they would hope for, or even evidence that the work that is crucial to finding out whether or not this could get seeded into the human population is happening. Do you have any response to that?
Its a complicated situation as far as [there are] new partners and new individuals and a different group of farm workers. Were doing everything we can and thinking about messaging, multilingual messages, communications, PPE [personal protective equipment], biosecurity on farms, and collaboration with USDA to really protect workers. That is definitely one of our highest priorities, and it always is.
But also were really thinking about this in the medium and longer term of what allowing a virus to circulate within a new mammalian host could mean. I dont think anybody really can predict what might happen, but we certainly know flu viruses change. And we do not want to give the virus that opportunity, if we can avoid it.
By the way, I think you need to add to your statue collection. The chicken needs a cow.
Yeah.
On data sharing, we are trying to be as forthcoming and as transparent as we can with the data that we have. I think were doing that in the Spotlights that were putting out every Friday. We got the Texas human virus sequence out as quickly as we could.
So I think were trying to do that as much as we can. We can always do more. But a lot of this, again, is our partnerships with the states. We defer to them. We have to be behind the scenes and let them talk about whats going on in their state.
Can I ask about your personal read on the risk here? If this virus gets seeded into the cow population and it evolves in cows, what do you think this does to the human risk from H5N1?
[Dugan grimaced.] I think it would definitely impact the risk, for sure. Our current assessment of the risk to the general public health is low. That could change. And so I think were remaining very vigilant if anything, more vigilant in this space.
These viruses change. If this were to become seeded in cows and become a cow-endemic virus, it certainly would increase that risk to people.
And certainly our pandemic planning [operation] has been really thinking about this and trying to be as vigilant as we can now, to try and understand not just current risk, but the future risk so that were as prepared as we can be.
But the risk could be quite big.
You said you still think the risk is low. But 15 years ago this spring, CDC was notified about two kids from California who had tested positive for swine flu who hadnt had exposure to pigs or each other. Before April 17, 2009, the risk of a swine flu pandemic would have seemed pretty low. And then CDC got those two samples, and everything changed really fast. Do you think about that?
Well, yeah. Its probably why Im not sleeping very much right now.
I think that the threat of a pandemic is always looming in the flu space. The way that Dan Jernigan [Dugans predecessor] always described public health to me is that it is an art form. Theres a balance that you have to strike. Theres a difference in the pandemic risk versus the immediate risk right now. And so I think thats what were trying to message to the average person who is walking about and living their lives. The risk to them is low.
But youre right. It could absolutely change.
