Fears are growing that the H5N1 outbreak among cattle in the United States may have been caused by contaminated animal feed.
Unlike Britain and Europe, American farmers are still allowed to feed cattle and other livestock the ground waste of other animals, including birds.
The U.S. Food and Drug Administration (FDA) is now reviewing the safety of this policy, a spokesperson said Tuesday.
Dairy cows and at least one farm worker in six US states have been infected with the highly pathogenic virus that has killed millions of animals worldwide since 2021.
A farm worker in Texas who is thought to have contracted the disease through infected cattle is the second recorded human case of H5N1 in the United States; However, WHO’s senior advisor on influenza, Dr. According to Joshua Mott, 8,000 possible exposures are currently being investigated.
This development is worrying because it allows the virus that has killed millions of birds and wild mammals worldwide to mutate further.
Experts fear that H5N1, first detected in cows a few weeks ago, may have been transmitted through a type of cattle feed called “poultry litter,” which consists of poultry feces, spilled feed, feathers and other waste scraped from poultry. floors of industrial chicken and turkey production facilities.
In the UK and EU, feeding cows proteins from other animals has been tightly regulated since the emergence of BSE (or ‘mad cow disease’) 30 years ago.
Experts aren’t sure, but they fear it may be the poultry litter feed used in the US that transmitted the virus to cattle.
Royal Population Medicine Associate Professor Dr. “Feeding poultry litter to beef cows in the US is a known cause of botulism in cattle and is a risk in the case of H5N1,” said Steve Van Winden. Veterinary College.
Virologist and researcher Dr. from the Pirbright Institute. Tom Peacock agrees: “This latest case would not be the first where there are concerns that H5N1 could be transmitted from different mammals through contaminated feed.” Last year, experts in Poland suspected it might have been contaminated 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; The most famous of these is the use of hormones in raising cattle for meat.
Although the presence of H5N1 in U.S. cattle herds increases the risk of transmission of the virus to humans through farm workers, it is the spread of the virus to hog farms that poses the greater threat.
This is because pigs have receptors similar to humans in some cells; This makes it much more likely that if pig farms become infected, the virus will mutate and jump to humans.
But so far the virus has not shown any worrying signs of mutation.
“H5N1 infection in pigs is of particular concern; pigs are extremely susceptible to human influenza virus strains, so can act as mixing vessels for bird and human viruses to mix and produce viruses that can infect humans more efficiently,” Dr Tom Peacock said.
In addition to being cheaper than other food sources such as soy and grains, poultry litter is also more calorie-dense; This means farmers can grow their herds much faster.
The practice is safe, according to the FDA’s previous statements: “With respect to pathogenic microorganisms, drug residues, and contaminants in poultry litter, FDA is not aware of any data indicating that the use of poultry litter in cattle feed causes human or animal harm.” health risks that warrant restrictions on its use,” the agency previously stated.
But that decision is currently “under review”, the agency told The Telegraph on Tuesday.
There are other theories about how cattle infected with H5N1, which has been detected so far in Texas, Idaho, Kansas, Ohio, New Mexico and Michigan, contracted the virus.
Many experts argue that the most likely route of infection is through wild birds found dead on some farms.
“The spread of this worldwide depends on wild and feral bird populations, where they land and where their droppings go,” stressed Dr Johsua Mott of the World Health Organisation.
“At some point, contact with wild birds in the environment produced the virus to which the cows were exposed, but how this exposure occurred is what many people are trying to understand,” he added.
Dr Mott said it was also unclear whether the virus spread from animal to animal.
More than one creature was infected on each farm, but this may have been because they ate a common source of infection (feed or wild birds) rather than transmitting the infection to another.
Mark Lyons, director of ruminant health for the United States Department of Agriculture, suggested at a meeting last week that the virus could potentially be transmitted through contamination of workers’ clothing or through suction cups attached to cow udders during milking.
But others argue that poultry litter cannot be ruled out as a potential source of contamination.
“Influenza can be spread via the faecal-oral route, and so it is not an impossible scenario for H5N1-infected chickens to shed live virus through the faces that cattle subsequently consume, and is therefore a potential mechanism of transmission. There are other explanations,” said Dr. Brian, Professor of Infectious Diseases at the University of Cambridge. Ferguson.
“The BSE scandal showed us the realities of what can happen when biosecurity is not a priority and showed us that biosecurity really needs to be prioritized – which is not always the case due to economics,” he added.
Although large-scale culling of poultry flocks has been undertaken to limit spread during outbreaks, it appears that a similar approach will not be adopted for cattle.
The CDC advised farmers with affected herds to discard milk produced by infected cattle; however, the pasteurization process is also thought to destroy the virus; This means that the risk of people consuming animal products remains low.
At this time, the WHO said the risk to humans is considered low but surveillance efforts should continue.
“There were 12 H5N1 cases worldwide in 2023 and a similar pace so far in 2024. There have been more than 800 cases worldwide since it emerged in 1996.
“So you get the sense that there’s nothing unprecedented in the number of human cases we’re seeing, but we do need to monitor the virus. We need to monitor the epidemiology to see if it changes in some way,” Dr Mott said.
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