Nobody saw this coming.
Dairy cows have not been affected before in the United States, or anywhere else in the world to my knowledge, and we've never before seen such clear evidence of mammal-to-mammal transmission.
It is quite intriguing that bovines were largely unaffected by influenza A, even though most of the domesticated and wild animals/birds at the human–animal interface succumbed to infection over the past few decades. Influenza A occurs on a very infrequent basis in bovine species and hence bovines were not considered to be susceptible hosts for influenza until the emergence of influenza D.
“A colleague of mine, he told me, ‘You know what’s strange? I went to one of my dairies last week, and all their cats were missing. I couldn’t figure it out — the cats usually come to my vet truck,’ ” Petersen recalled. “And then someone called me and said half of his cats had passed away without warning, and so then all the alarm bells start going off in your head.”
The cats had died from swollen brains, a potential result of influenza.
The H5N1 bird flu outbreak in dairy cows in the United States has likely been going on for months longer than was previously realized, and has probably spread more widely across the country than the confirmed outbreaks would imply, according to an analysis of genetic sequences that were released Sunday by the U.S. Department of Agriculture. (...)
The genetic sequences cluster too closely for this to be anything other than a single spillover, Worobey said. “If it were jumping from bird to cattle over and over again … I wouldn’t think you would just get this same very reduced genetic diversity where each of the internal segments are showing the same pattern.”
According to our GenoFlu analysis, the B3.7 genotype represents a 4+4 reassortant strain, with the HA, NA, PA, and MP genes originating from the H5N1 virus strain in 2020, while the remaining segments (PB2, PB1, NP, and NS) are closely related to LPAI viruses.
Cattle Farming
Before March 2024 there were no reports about H5N1 infections in cows outside of a laboratory experiment with high viral doses. Cattle was considered to not be very susceptible of influenza in general. Keeping large quantities of cows, often outside on pastures, has so far been considered a minor risk from a public health perspective. However, large quantities of cows could enable long chains of infection, which would be hard to detect since cows exhibit only minor symptoms. Recent infections of cows with H5N1 are attributed to contact with wild birds and coincide with the first documented cases of H5N1 in goats. Once again the issue is exacerbated by a lack of surveillance.
Our findings show that HPAIV (H5N1) has the potential to infect bovine calves, at least after high-titer intranasal inoculation, and that conventional HI tests may underestimate such infections. Furthermore, asymptomatic shedding of HPAIV (H5N1) by infected calves and subsequent seroconversion seem to be possible, and even low levels of HPAIV (H5N1) might be sufficient to induce a detectable antibody response in contact calves. However, the possibility that the infectivity detected in the contact calf at 1 dpi was the result of residual inoculum cannot be ruled out. Although the question whether calf-to-calf transmission of HPAIV (H5N1) occurs could not be definitely answered by our study, bird-to-calf transmission resulting in seroconversion is probable.
As of Monday, March 25, unpasteurized, clinical samples of milk from sick cattle collected from two dairy farms in Kansas and one in Texas, as well as an oropharyngeal swab from another dairy in Texas, have tested positive for highly pathogenic avian influenza (HPAI). Additional testing was initiated on Friday, March 22, and over the weekend because farms have also reported finding deceased wild birds on their properties. Based on findings from Texas, the detections appear to have been introduced by wild birds. Initial testing by the National Veterinary Services Laboratories has not found changes to the virus that would make it more transmissible to humans, which would indicate that the current risk to the public remains low.
Our findings are that there are closer to 1.5 billion cows worldwide. However, according to 2023 studies by USDA, there are approximately 1 billion (942,630 to be exact) cattle stocks in the world.
In 2014, according to Our World in Data, cattle stocks numbered 1.47 billion head of cattle worldwide.
It's perhaps not as well known as it should be that many 'strict herbivores' will eat animal matter on occasion. Sometimes this behaviour is absolutely deliberate and likely motivated by a need for calcium: antler- and bone-eating is common in deer and other hoofed mammals, and the consumption of seabird chick heads, wings and legs by island-dwelling deer and sheep is well documented (Furness 1988). Red deer Cervus elaphus that eat seabirds seem to deliberately eat the bones only, and carefully avoid ingesting the flesh. White-tailed deer Odocoileus virginianus and domestic cattle Bos taurus have been shown (thanks again to remote cameras) to consume passerine and quail nestlings and/or eggs when they discover them (Pietz & Granfors 2000, Nack & Ribic 2005, Ellis-Felege et al. 2008): this behaviour is likely opportunistic, but may well be common and widespread (it's difficult to document since it mostly occurs at night and no evidence remains).
For the dairies whose herds are exhibiting symptoms, on average about ten percent of each affected herd appears to be impacted, with little to no associated mortality reported among the animals.
Mammal-to-Mammal Transmission
Detections in multiple states and a larger percentage of infected cows have lead to speculations about mammal-to-mammal transmission. Even airborne transmission has been speculated about. A human case related to cattle has lead to further speculations. However, the transmission via respiratory droplets is highly unlikely. While one factor may be transmission through saliva due to cows licking each other, the focus is currently on milk and milking instruments, due to high concentrations of virus found in milk. Apparently the outbreak started as early as late December 2023 and was not detected for months. The virus has spread to at 30 farms in several US states, but testing of milk reveals that the presence of bird flu in cows is already a widespread phenomenon.
To date, we have not found significant
concentration of virus in respiratory related samples,
which indicates to us that respiratory transmission is
not a primary means of transmission.
I want to emphasize really how unusual this is. In other mammalian species with influenza viruses, it's primarily a respiratory disease, which doesn't seem to be the case in these cattle.
If there is cow-to-cow transmission, how does it work? It’s clear that it’s dairy cows, and it could be that it’s due to the milking instruments that do not get cleaned enough. It’s human driven cow-to-cow transmission. And if that’s the case, you can stop it.
As of Monday, March 25, unpasteurized, clinical samples of milk from sick cattle collected from two dairy farms in Kansas and one in Texas, as well as an oropharyngeal swab from another dairy in Texas, have tested positive for highly pathogenic avian influenza (HPAI). Additional testing was initiated on Friday, March 22, and over the weekend because farms have also reported finding deceased wild birds on their properties. Based on findings from Texas, the detections appear to have been introduced by wild birds. Initial testing by the National Veterinary Services Laboratories has not found changes to the virus that would make it more transmissible to humans, which would indicate that the current risk to the public remains low.
The Texas Department of State Health Services is reporting a human case of avian influenza A(H5N1) virus in Texas. The case was identified in a person who had direct exposure to dairy cattle presumed to be infected with avian influenza.
Allogrooming, which generally involves one cow licking another around the head and neck, is believed to serve a number of social purposes. For instance, social grooming is both a way to establish individual bonds between members of a group and also enhances overall social cohesion in the herd.
Has USDA confirmed at this point that cow-to-cow
transmission is a factor?
Yes, although it is unclear exactly how virus is being
moved around. We know that the virus is shed in milk at
high concentrations; therefore, anything that comes in
contact with unpasteurized milk, spilled milk, etc. may
spread the virus.
The report of the US human case brings forth several important issues including the question of whether this signals a global pandemic in the making? Foremost, how has transmission in cows and from cow to human occurred? Infected cows show symptoms such as decreased lactation, anorexia, lethargy, fever and dehydration, raising concerns of an increased risk of H5N1 viruses becoming better adapted to mammals with enhanced potential to spilling over to humans and other livestock. It has been suggested that A(H5N1) might not be spreading among cows through the air. The current thought is that the virus has spread via the use of contaminated milking equipment between infected and uninfected cows. How a virus that causes respiratory tract disease ends up in cow udders, and is detectable in milk, and whether other organs are infected is important to elucidate. No infection in beef cattle has been detected yet, but this could be due to sub-clinical or mild symptoms and lack of active surveillance.
Scaling up of the production of human vaccines against the new A(H5N1) variants seems imperative, primarily to protect high-risk individuals such as farm workers against infection, but also for stockpiling, and secondly to increase preparedness should the virus evolve to sustained human-to-human transmission. Culling of poultry has so far not resulted in controlling the zoonotic pandemic (enzootic) of A(H5N1); perhaps a shift towards prevention instead, by the vaccination of farm animals and farm workers needs to be considered.
It is quite intriguing that bovines were largely unaffected by influenza A, even though most of the domesticated and wild animals/birds at the human–animal interface succumbed to infection over the past few decades. Influenza A occurs on a very infrequent basis in bovine species and hence bovines were not considered to be susceptible hosts for influenza until the emergence of influenza D.
A strain of highly pathogenic avian influenza has been silently spreading in US cattle for months, according to preliminary analysis of genomic data. The outbreak is likely to have begun when the virus jumped from an infected bird into a cow, probably around late December or early January. This implies a protracted, undetected spread of the virus — suggesting that more cattle across the United States, and even in neighbouring regions, could have been infected with avian influenza than currently reported. (...)
Analysis of the genomes suggests that the cattle outbreak probably began with a single introduction from wild birds in December or early January. (...) The data also show occasional jumps back from infected cows to birds and cats. “This is a multi-host outbreak,” says Nelson.
The genomic data reveal that the viral genome sequenced from the infected person does not include some of the signature mutations observed in the cattle. “That is a mystery to everyone,” says Nelson.
One possibility is that the person was infected by a separate viral lineage, which infected cattle that have not been swabbed. Another less likely scenario, which can’t be ruled out, says Nelson, is that the person was infected directly from a wild bird. “It raises just a whole slew of questions about what black box of samples we are missing.”
We genetically characterize HPAI viruses from dairy cattle showing an abrupt drop in milk production. They share nearly identical genome sequences, forming a new genotype B3.13 within the 2.3.4.4b clade. B3.13 viruses underwent two reassortment events since 2023 and exhibit critical mutations in HA, M1, and NS genes but lack critical mutations in PB2 and PB1 genes, which enhance virulence or adaptation to mammals.
The duck and human IAV receptors were widely expressed in the bovine mammary gland, whereas the chicken receptor dominated the respiratory tract. In general, only a low expression of IAV receptors was observed in the neurons of the cerebrum. These results provide a mechanistic rationale for the high levels of H5N1 virus reported in infected bovine milk and show cattle have the potential to act as a mixing vessel for novel IAV generation.
Without changes in HA affecting receptor binding, the risk of the virus becoming transmissible between humans is low. The lack of HA changes may also suggest (at least with the current tissue tropism) that there is not strong selective pressure to change receptor binding, suggesting ‘avian-like’ α-2,3-linked sialic acids are abundant in the main sites of replication in these animals. However, this is also true for dogs and pigs, which in the short term do not strongly select for such changes, yet in the longer term, avian-origin H1N1 and H3N2 viruses in these species gradually adapt to ‘human-like’ α-2,6-linked sialic acids.
H5N1 is transmitting from cattle back into wild birds, poultry, cats, and other species.
Milk
Milk is usually pasteurized and therefore safe to consume, since all pathogens including avian influenza are deactivated by the heat.
As of Monday, March 25, unpasteurized, clinical samples of milk from sick cattle collected from two dairy farms in Kansas and one in Texas, as well as an oropharyngeal swab from another dairy in Texas, have tested positive for highly pathogenic avian influenza (HPAI).
At this stage, there is no concern about the safety of the commercial milk supply or that this circumstance poses a risk to consumer health. Dairies are required to send only milk from healthy animals into processing for human consumption; milk from impacted animals is being diverted or destroyed so that it does not enter the food supply. In addition, pasteurization has continually proven to inactivate bacteria and viruses, like influenza, in milk. Pasteurization is required for any milk entering interstate commerce.
H5N1 virus lost infectivity after 30 min at 56°C
Pasteurization of milk, widely practiced in several countries, notably the United States, requires temperatures of about 63 °C (145 °F) maintained for 30 minutes or, alternatively, heating to a higher temperature, 72 °C (162 °F), and holding for 15 seconds (and yet higher temperatures for shorter periods of time).
The FDA recognizes two pasteurization methods: high-temperature short-time (HTST) and ultra-high-temperature (UHT) pasteurization. HTST pasteurization requires heating milk to 161°F for 15 seconds, while UHT pasteurization involves heating milk to 280°F for 2 seconds. The specific pasteurization requirements are stated in the Code of Federal Regulations, Title 21, Part 131, Subpart D, Section 131.150.
Consumers of unpasteurized milk and cheese are a small proportion of the U.S. population — 3.2 percent and 1.6 percent, respectively — but compared with consumers of pasteurized dairy products, they are 838.8 times more likely to experience an illness and 45.1 times more likely to be hospitalized.
Testing conducted by the Food and Drug Administration on pasteurized commercially purchased milk has found genetic evidence of the H5N1 bird flu virus, the agency confirmed Tuesday. But the testing, done by polymerase chain reaction, or PCR, cannot distinguish between live virus or fragments of viruses that could have been killed by the pasteurization process. (...) “Pasteurization kills much sturdier viruses than influenza, so we expect it to work,” said Andrew Pekosz, a molecular microbiologist who studies respiratory viruses at Johns Hopkins Bloomberg School of Public Health. “But it’d be great to have the data.
In conclusion, this article documents a pattern between an earlier time in which anxiety over falling wages and increasing domestic immigration focused on issues of meat and dairy consumption and current anxiety over stagnant wages, fears over immigration, and a reassertion of the consumption of milk and dairy as a proxy reassertion of white privilege.
He knew the Food and Drug Administration was working on its own national survey of the milk supply. But he was impatient. So he and a graduate student went on a road trip: They collected 150 commercial milk products from around the Midwest, representing dairy processing plants in 10 different states, including some where herds have tested positive for H5N1. Genetic testing found viral RNA in 58 samples, he told STAT.
A senior official from the US Food and Drug Administration (FDA) said today that its nationwide survey of retail milk has found remnants of H5N1 avian flu viruses in one in five samples, with the highest concentrations in regions where outbreaks in dairy cattle have been reported.
In all matrices, including human milk, pasteurization at 62.5 °C was generally sufficient to reduce surviving viral load by several logs or to below the limit of detection. Holder pasteurization (62.5 °C, 30 min) of human milk should be sufficient to inactivate nonheat resistant viruses, including coronaviruses, if present.
The fact that you can go into a supermarket and 30% to 40% of those samples test positive, that suggests there’s more of the virus around than is currently being recognized.
Poultry Litter
Poultry litter consists mostly of poultry excrement and is used as feed for livestock. It is fed to beef cows, but usually not dairy cows.
UC Davis’ Payne said that in California, poultry waste is processed at high virus-killing temperatures, so it is unlikely to be a concern. The practice is banned in the United Kingdom, European Union and Canada, where fears of spreading bovine spongiform encephalitis — mad cow disease — made such practices seem too risky.
Representatives of the beef and poultry industry argue that the overall costs to the beef industry – and, ultimately, the consumer – would far outweigh any ‘”limited” potential safety gains from banning poultry litter as a cattle feed. They also claim that any ban would exacerbate the existing problem of the mass disposal of poultry litter from factory farms. In defending their right to feed poultry litter to cattle, the National Cattlemen’s Beef Association recently said that “we must continue to look to the science to avoid over-regulating the industry and creating policy that doesn’t meet our objective of a safer animal health system.”
The fact that certain elements within the food and farming industry are willing to publicly defend the feeding of poultry litter to cattle – that is chicken feces, feathers and other poultry debris collected from the floors of factory farms – on the basis that this represents a “safer animal health system” is an appalling indictment of the state of US food and farming. It also is a stark warning to us all of the huge chasm that has emerged between how most of us think our food is being produced and the appalling practices that are justified by those who are so deeply embroiled in the drive to produce ever cheaper meat that they no longer have any sense of what is accepted as the norm.
Adding broiler litter to beef cattle rations at a level of 20% or higher (as fed basis) generally meets the animal's needs for crude protein, calcium, and phosphorus. (...) Broiler litter to be used for cattle feed should contain at least 75% dry matter. If litter contains less than 70% dry matter, wet spots and mold can be problems. Since litter may contain scrap metal, the material should be run through a hammermill equipped with a magnet to remove objects that may cause hardware disease. In addition, the material should be screened to remove pieces of wood, glass, etc.
Animal wastes represent a vast reservoir of cheap nutrients, particularly for ruminants. In most countries, waste, particularly from poultry, is easily collected, as it is concentrated in small areas, and its cost, as a raw material for feed, is generally the cost of transport alone. The only expensive item may be processing, but this cost is relatively small and is recoverable from the profit arising out of the low original cost. Feed costs for dairy or beef cattle usually represent 50–80% of the total production costs; this can be reduced to 20–40% by utilizing these new feed resources as donors of protein, minerals and other nutrients.(...)The calculated mean energy values of animal wastes for ruminants, estimated in Table 8, indicate that only broiler manure and broiler litter exhibit a TDN value comparable to conventional feed ingredients (Müller, 1975e). The other livestock wastes are low in feed energy, at levels comparable to crop residues.
It seems ghoulish, but it is a perfectly legal and common practice for chicken litter — the material that accumulates on the floor of chicken growing facilities — to be fed to cattle.
"Bovine Influenza A Virus (BIAV)"
"Bovine Influenza A Virus (BIAV)" is a marketing term designed to distract from the fact that cows get bird flu.
But the American Association of Bovine Practitioners (AABP), an organization of beef and dairy veterinarians, declared in a statement (condemned by public health experts) last week that it doesn’t believe bird flu in cows should be considered bird flu at all.
“The AABP will call this disease Bovine Influenza A Virus (BIAV),” the association’s executive director K. Fred Gingrich II and president Michael Capel said in a statement, encouraging federal and state regulators to do the same. “It is important for the public to understand the difference to maintain confidence in the safety and accessibility of beef and dairy products for consumers.”
In other words, industry vets are trying to rebrand bird flu so that we keep calm and keep buying cheeseburgers. “They’re worried about selling products,” bovine veterinarian James Reynolds, a professor at Western University’s vet school, told me, calling the group’s statement “disease-washing.”
What is the appropriate nomenclature for this virus, now that it has appeared in dairy cows?
From USDA’s perspective, highly pathogenic avian influenza or H5N1 are the most scientifically accurate terms to describe this virus. This is also consistent with what the scientific community has continued to call the virus after it has affected other mammals.
Biosecurity
So far there is no readily available vaccine, no culling of infected herds, but at least limited mandatory testing of cattle herds being oved across USA state borders. While an important factor is that bird flu in cows is a new phenomenon, and testing resources are always limited, there is also no economic incentive to cull or even vaccinate cattle. While infected dairy cows produce less milk, this doesn't apply to beef cattle.
We don’t have a good sense of the spread because testing is voluntary and certainly not being done in a systematic way. We’re pretty much flying blind with the testing aspect.
ARS has begun to assess the potential to develop an
effective vaccine for H5N1 in bovine. It is difficult to
predict how long development might take, as many
outstanding questions remain about the transmission to
cattle, characterizations of the infection, etc.
It is important to keep in mind that while H5N1 is highly
pathogenic in birds, that is not the case in cattle. At this
time, APHIS does not think it would be practical,
feasible or necessarily informative to require mandatory
testing, for several reasons ranging from laboratory
capacity to testing turnaround times. We are working
actively to learn more about the emergence of H5N1 in
cattle, but right now we are seeing that a small portion
of the affected herds are becoming ill, and that the
number of herds exhibiting symptoms is relatively small.
For context, there are more than 26,000 dairy herds
nationwide. We are strongly recommending testing
before herds are moved between states, which should
both give us more testing information, and should
mitigate further state-to-state spread between herds.
The fate of the cows is another matter. So far, the USDA hasn’t issued orders to quarantine cattle, but it recommends minimizing their movement. Some states are restricting the import of cattle from states with infected herds.
The USDA has required poultry farmers to cull flocks infected with H5N1, leading to the loss of 85 million birds to date. Nothing this severe is being suggested for cows, but there are big concerns about what could happen if the virus in them spreads to poultry and leads to new infections in flocks.
Part of the problem, some experts said, is that the U.S.D.A. has long been in the position of both regulating and promoting the business of agriculture.
It says farmers only have to test up to 30 animals in a given group. The guidance does not say how farmers should determine which 30 animals to test in larger groups that are being readied to be moved. (...) While pragmatic, researchers who spoke to STAT were split on whether the policy will be effective. Anice Lowen, an influenza researcher at Emory University School of Medicine, told STAT via email that the approach is likely sufficient to detect an H5N1-positive herd. “I think this approach is reasonable,” she said. Nuzzo had concerns, however, that in very large herds, like those around 500 or more, infected animals could be missed.
As of April 24, 2024, USDA has confirmed H5N1 virus
detections on 33 dairy cattle premises in 8 states
(Kansas, Idaho, Michigan, New Mexico, North Carolina,
Ohio, South Dakota, Texas). USDA has also confirmed -
based on specific phylogenetic evidence and
epidemiological information - that 8 poultry premises in
5 states (Kansas, Michigan, Minnesota, New Mexico and
Texas) have also been infected with the same distinct
H5N1 virus genotype detected in dairy cattle.
Epidemiologists from the agency were ultimately unable to access a Texas dairy farm where a human was infected with the virus in March, they disclosed in attachments to the report published Friday by the New England Journal of Medicine. That prevented investigators from being able to investigate how workers might have been exposed to the virus on the farm.
That is because the dairy worker who came to a Texas field office for testing "did not disclose the name of their workplace," said Lara Anton, a spokesperson for the Texas Department of State Health Services.
They also were unable to collect follow-up samples from the dairy farm worker or their contacts, which could have revealed missed cases as well as tracking the virus and antibodies against it in the body after an infection.
The Centers for Disease Control and Prevention recommended this week that dairy and poultry farms with infected animals supply protective gear to workers in a bid to stave off human transmission of the H5N1 virus. The challenge now is making it happen.
The CDC has no legal authority to order those protective measures, and health officials in some of the nine states with reported outbreaks in cattle have had little luck getting farmers to take them up on offers of free personal protective equipment for their workers, even as the virus continues to spread.
During a briefing for reporters Wednesday, Vivien Dugan, director of the influenza division at the Centers for Disease Control and Prevention, said dairy worker vaccination might begin if any worrisome new changes are detected about the virus, such as changes in its genetic code.