Fears are growing that the H5N1 outbreak among cattle in the United States could have been caused by contaminated animal feed.
In contrast to Britain and Europe, American farmers are still allowed to feed cattle and other farm animals ground-up waste from other animals including birds.
Dairy cows across six US states – and at least one farm worker – have become infected with the highly pathogenic virus, which has already killed millions of animals across the globe since 2021.
The farm worker, who is thought to have been exposed via infected cattle in Texas, is only the second recorded human H5N1 case in the US. Since February, the US has investigated and discounted a further 8,000 possible exposures, according to Dr Joshua Mott, WHO senior advisor on influenza.
The development is of concern because it allows the virus, which has killed millions of birds and wild mammals around the world, more opportunities to mutate.
Experts fear that H5N1, which was only first detected in cows a few weeks ago, may have been transmitted through a type of cattle feed called “poultry litter” – a mix of poultry excreta, spilled feed, feathers, and other waste scraped from the floors of industrial chicken and turkey production plants.
In the UK and EU, feeding cows proteins from other animals has been tightly regulated since the outbreak of BSE – or ‘mad cow disease’ – 30 years ago.
Experts are unsure but fear it could be the poultry litter feed used in the US that has passed the virus to cattle.
“In the US, the feeding of poultry litter to beef cows is a known factor in the cause of botulism in cattle, and is a risk in the case of H5N1,” said Dr Steve Van Winden, Associate Professor in Population Medicine at the Royal Veterinary College.
Dr Tom Peacock, a virologist and fellow at the Pirbright Institute agreed: “This latest case wouldn’t be the first time there have been concerns H5N1 could be moving through different mammals via contaminated feed,” citing the outbreak of avian flu in cats in Poland last year, which experts suspected might have been transmitted through mink byproducts used in raw cat food.
The US cattle industry is worth over $100 billion and regulations covering animal standards there have long been controversial in Europe – most famously over the use of hormones in the rearing of cattle for meat.
Although the presence of H5N1 in US cattle herds increases the risk of the virus getting into humans via farm workers, it is the spread of the virus to pig farms that presents the bigger threat.
This is because pigs have receptors on some cells that are similar to humans, making it much more likely that the virus could mutate and jump to humans if pig farms become infected.
So far, the virus hasn’t shown any signs of worrying mutation, however.
“Infection of H5N1 in pigs is of particular concern – they are highly susceptible to human influenza virus strains so could act as mixing vessels for avian and human viruses to mix and generate viruses that can more efficiently infect humans,” said Dr Tom Peacock.
Poultry litter is not only cheaper than other food sources like soy and grains but is also more calorie-dense, meaning farmers can bulk up their herds much more quickly.
According to previous statements by the FDA, the practice is safe: “With respect to pathogenic microorganisms, drug residues and contaminants in poultry litter, FDA is not aware of any data showing that the use of poultry litter in cattle feed is posing human or animal health risks that warrant restrictions on its use,” the agency previously noted.
There are several other theories on how the H5N1-infected cattle – so far identified in Texas, Idaho, Kansas, Ohio, New Mexico, and Michigan – contracted the virus.
Many experts argue that the most likely route of infection is via wild birds – which have been found dead on some farms.
“The spread of this around the world comes back to wild and wild bird populations and where they land and where their faeces goes,” stressed the WHO’s Dr Johsua Mott.
“At some point, the contact with wild birds in the environment produced virus that then the cows had exposure to, but how that exposure happened is what many people are trying to figure out,” he added.
It is also unclear if the virus is spreading from animal to animal, said Dr Mott.
On each farm, multiple creatures have been infected but this could be because they are eating from a common source of infection – feed or wild birds – rather than passing it on to another.
The director of ruminant health for the United States Department of Agriculture, Mark Lyons, suggested at a meeting last week the virus could be potentially transmitted by contamination of workers’ clothing, or the suction cups that are attached to cow udders during milking.
However, others argue that poultry litter as a potential source of contamination cannot be ruled out.
Fears are growing that the H5N1 outbreak among cattle in the United States could have been caused by contaminated animal feed.
In contrast to Britain and Europe, American farmers are still allowed to feed cattle and other farm animals ground-up waste from other animals including birds.
Dairy cows across six US states – and at least one farm worker – have become infected with the highly pathogenic virus, which has already killed millions of animals across the globe since 2021.
The farm worker, who is thought to have been exposed via infected cattle in Texas, is only the second recorded human H5N1 case in the US. Since February, the US has investigated and discounted a further 8,000 possible exposures, according to Dr Joshua Mott, WHO senior advisor on influenza.
The development is of concern because it allows the virus, which has killed millions of birds and wild mammals around the world, more opportunities to mutate.
Experts fear that H5N1, which was only first detected in cows a few weeks ago, may have been transmitted through a type of cattle feed called “poultry litter” – a mix of poultry excreta, spilled feed, feathers, and other waste scraped from the floors of industrial chicken and turkey production plants.
In the UK and EU, feeding cows proteins from other animals has been tightly regulated since the outbreak of BSE – or ‘mad cow disease’ – 30 years ago.
Experts are unsure but fear it could be the poultry litter feed used in the US that has passed the virus to cattle.
“In the US, the feeding of poultry litter to beef cows is a known factor in the cause of botulism in cattle, and is a risk in the case of H5N1,” said Dr Steve Van Winden, Associate Professor in Population Medicine at the Royal Veterinary College.
Dr Tom Peacock, a virologist and fellow at the Pirbright Institute agreed: “This latest case wouldn’t be the first time there have been concerns H5N1 could be moving through different mammals via contaminated feed,” citing the outbreak of avian flu in cats in Poland last year, which experts suspected might have been transmitted through mink byproducts used in raw cat food.
The US cattle industry is worth over $100 billion and regulations covering animal standards there have long been controversial in Europe – most famously over the use of hormones in the rearing of cattle for meat.
This is because pigs have receptors on some cells that are similar to humans, making it much more likely that the virus could mutate and jump to humans if pig farms become infected.
So far, the virus hasn’t shown any signs of worrying mutation, however.
“Infection of H5N1 in pigs is of particular concern – they are highly susceptible to human influenza virus strains so could act as mixing vessels for avian and human viruses to mix and generate viruses that can more efficiently infect humans,” said Dr Tom Peacock.
Poultry litter is not only cheaper than other food sources like soy and grains but is also more calorie-dense, meaning farmers can bulk up their herds much more quickly.
According to previous statements by the FDA, the practice is safe: “With respect to pathogenic microorganisms, drug residues and contaminants in poultry litter, FDA is not aware of any data showing that the use of poultry litter in cattle feed is posing human or animal health risks that warrant restrictions on its use,” the agency previously noted.
There are several other theories on how the H5N1-infected cattle – so far identified in Texas, Idaho, Kansas, Ohio, New Mexico, and Michigan – contracted the virus.
Many experts argue that the most likely route of infection is via wild birds – which have been found dead on some farms.
“The spread of this around the world comes back to wild and wild bird populations and where they land and where their faeces goes,” stressed the WHO’s Dr Johsua Mott.
“At some point, the contact with wild birds in the environment produced virus that then the cows had exposure to, but how that exposure happened is what many people are trying to figure out,” he added.
It is also unclear if the virus is spreading from animal to animal, said Dr Mott.
On each farm, multiple creatures have been infected but this could be because they are eating from a common source of infection – feed or wild birds – rather than passing it on to another.
The director of ruminant health for the United States Department of Agriculture, Mark Lyons, suggested at a meeting last week the virus could be potentially transmitted by contamination of workers’ clothing, or the suction cups that are attached to cow udders during milking.
However, others argue that poultry litter as a potential source of contamination cannot be ruled out.
“The flu can be spread by faecal-oral routes, and so it’s not an impossible scenario that chickens who are infected with H5N1 are shedding live virus through faces, which the cattle then consume, and so it is a potential mechanism of transmission, although there are other explanations,” said Dr Brian Ferguson, Professor of Infectious Diseases at the University of Cambridge.
“The BSE scandal showed us the reality of what happens when biosecurity is not a priority, and showed us that it really does need to be prioritised – which is not always the case, because of the economics involved,” he added.
Despite large-scale culling in poultry flocks during outbreaks to limit spread, it seems a similar approach will not be taken for cattle.
The CDC has advised farmers with affected herds to dispose of milk produced by infected cattle, although it is thought that the pasteurisation process also destroys the virus – meaning the risk to humans consuming animal products remains low.
At present, the WHO has said the risk to humans is considered low, but that surveillance efforts must be kept up.
“There were 12 of H5N1 cases globally in 2023, and a similar pace so far in 2024. Since it emerged in 1996, there have been over 800 cases globally.
“So you get a sense that there’s nothing unprecedented about the number of human cases we’re seeing – but we have to watch the virus. We have to watch the epidemiology, to see if it’s changing in some way,” said Dr Mott.
Source: The Telegraph
