By Angus Dalton
Experts fear the risk of a bird flu pandemic is at an all-time high due to a severe form of the virus that has infected 69 people, killed one patient, ripped through 972 cattle herds and forced the culling of 162 million poultry birds in the US.
The problem H5N1 clade, or subgroup, is still a bird-adapted virus and the risk to the public remains low. All but three of the US cases in humans were traced back to infection by sick cows, poultry or other animals such as wild birds, and Australia remains free of the H5N1 strain.
A study tested 150 vets working with cows and found three had signs of recent bird flu infection. Credit: AP
But every animal infection – particularly in mammals – hands the virus an opportunity to develop random mutations that could allow transmission between people. Two recent developments and one “red flag” study have sharpened the need to restrict the virus’s chances of gaining that ability.
Cats sickened or killed
On Thanksgiving, a 14-year-old tabby cat named Alexander died in California. His owner had fed the cat raw milk that was later recalled because it was contaminated with bird flu, the Los Angeles Times reported. Tuxsie, a four-year-old tuxedo cat owned by the same man, died two days later. A third cat, named Big Boy, returned from hospital alive but blind.
Dozens of other cats sickened or killed by bird flu sparked the US Food and Drug Administration in January to order pet food manufacturers to minimise the hazard of H5N1 passing on to cats and dogs through raw meat, unpasteurised eggs and milk.
Two cats drinking raw milk later recalled due to bird flu contamination. Big Boy (left) survived after treatment but Alexander (right) died.Credit: Joseph Journell/AP
Most pet food is treated with heat to kill pathogens, but some US raw pet food suppliers have recalled products in response.
Cats haven’t been recorded transmitting bird flu to humans. However, a study analysing the deaths of 10 cats in South Dakota warned they could serve as “mixing vessels” for bird and mammal viruses and pose a risk to public health.
“Cats, common companion animals that frequently interact with humans and other species, could serve as a bridge for cross-species transmission of H5N1 viruses,” the authors reported in Emerging Microbes & Infections.
The study suggested free-roaming cats may also acquire the virus by eating infected birds.
More than 162 million chickens and ducks have been killed in the US amid the outbreak.Credit: Bloomberg
Trump administration accidentally fires bird flu workers
The US is a major melting pot for the H5N1 virus and experts have repeatedly emphasised the importance of tracking the spread of the virus through animal populations and into humans.
But the US Agriculture Department is scrambling to rehire employees working on the government’s response to the bird flu outbreak after they were accidentally fired as part of President Donald Trump’s massive staffing cuts to federal agencies.
The department said on Wednesday (AEDT) it would rescind termination letters sent under the recommendation of Elon Musk’s department of government efficiency to officials working on the virus response, AP reported.
A key study that discovered evidence of “silent” bird flu infections, released last week by the US Centres for Disease Control and Prevention (CDC), was also delayed for weeks by the Trump administration’s pause on health communications.
The study tested 150 vets working with cows and found three had signs of recent bird flu infection. Worryingly, one of the infected vets had only practised in Georgia and South Carolina – states with no known cases in cattle or people.
The results suggest the virulent clade of the virus is circulating in some areas within both people and cows, completely undetected.
The CDC said the finding highlighted the importance of rapidly identifying sick animals and monitoring people for flu.
Particles of H5N1 bird flu flagged in yellow.Credit: CDC
Mutation identified that could lead to human transmission
It’s difficult for bird flu to infect humans, and there is no evidence the virus can be transmitted between people.
H5N1 targets cell receptors called alpha-2,3 which are common in birds but buried deep within the lungs of humans, so they’re hard for the virus to reach. CDC analysis of the first US patient to die from bird flu, however, found the virus had mutated to better target receptors in the upper respiratory tract.
Californian scientists have also identified a single tweak to an amino acid on the virus’s binding protein would allow the virus to latch well onto human cells.
The mutation was made artificially in a lab, and it isn’t circulating in the real world, but the experiment demonstrated how easily the virus could evolve to better infect humans. Study co-author Professor James Paulson described the finding as a “red flag for possible adaptation to people”.
The virus would need several other mutations to spread and replicate effectively within human cells and pose a pandemic threat. But Andy Pekosz, a professor of molecular microbiology and immunology at Johns Hopkins University, warned we should “absolutely” be concerned about person-to-person transmission.
“We’re seeing signs that this virus is really moving into humans,” he said. “We have no evidence of transmission yet, but we need to do more surveillance in broader populations that are at risk.”
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