The so-called “bird flu” H5N1 virus only rarely infects humans. Over the course of several decades during which it has circulated and resulted in the deaths of tens of millions of birds, about 880 cases in humans have been reported, generally in humans who work very closely with livestock.
But when it does make the leap to human hosts, H5N1 is often lethal — out of 26 cases reported since 2022, seven people died. That’s why it’s troubling that H5N1 has been recently discovered to have quietly spread across the country’s (USA) dairy farms, with testing finding genetic material of the virus present in 1 in 5 milk samples across the US. (Pasteurization kills the virus, so milk remains safe to drink. - I will touch base on this subject on another thread soon)
That prevalence suggests that H5N1 is now spreading in mammals — and since cows on dairy farms are in frequent contact with farm workers, it seems likely the virus will have many chances to evolve to spread more easily among humans.
Mia Kim Torchetti, a veterinarian who directs the USDA’s Diagnostic Virology Laboratory at the National Veterinary Services Laboratories in Ames, Iowa, says she had hoped this incursion could be stamped out quickly, but as detections in birds and mammals pile up, “I have rapidly lost hope.”
Though all public health agencies consider the risk of the bird flu spreading widely in people to be low, the outbreak is still reminiscent of the early days of the COVID-19 pandemic.
It has already spilled over to 20 mammalian species.
Torchetti further says,
"We often call the avian influenza virus currently infecting cattle by its nickname, H5N1 bird flu. But its full name is “highly pathogenic avian influenza A H5N1 clade 2.3.4.4b genotype B3.13.”
That specificity denotes the virus’ place in its family tree. Highly pathogenic avian influenza A H5N1 viruses — which are deadly to chickens and related birds — are a huge family tree of bird flu viruses. They all have the H5 form of hemagglutinin, a protein that latches onto host cells so the virus can infect them. The first highly pathogenic avian influenza H5N1 virus was found in 1996. Since then, scientists have documented the tree’s expansion, with some limbs dying off and others making it big. One successful limb of the tree is clade 2.3.4.4b. It has sprouted branches of its own, including genotype B3.13.
Various H5N1s have winged their way around the world after infecting wild birds. A different version crossed the Atlantic in 2014 and caused an outbreak in North American poultry in 2015, but it didn’t take hold, This time is different."
Clade 2.3.4.4 viruses have been infecting poultry and wild birds for several years. But the limb of the tree we’re dealing with now — H5N1 clade 2.3.4.4b — emerged in Europe in October 2020 when two bird flu viruses swapped parts. It came to the Americas in 2021. It has killed more than 90 million birds in the United States since January 2022, including wild birds and commercial poultry and backyard and hobbyist flocks that were culled when the virus was detected.
Influenza viruses are all about the swap meet.
Instead of one long novel, the genetic instruction books of influenza A viruses are more like a series of eight novellas, known as gene segments. Each segment carries one or more of the 11 genes that the virus needs to infect host cells and copy itself. When people, birds or other animals are simultaneously infected with more than one type of influenza virus, the viruses may exchange segments and thus create a new type of virus. This process — called reassortment — has resulted in pandemic strains of flu, including the 1918 influenza pandemic and 2009’s swine flu.
Viruses can’t swap parts willy-nilly. Not all combinations are compatible with each other. But what’s unusual about this clade of H5N1s is that it undergoes reassortment far more often than earlier relatives, Torchetti says.
No one knows exactly where, when and how the virus passed from wild birds into cattle. Cows may have grazed on grass that wild birds carrying the virus pooped on, or the cows may have picked it up through contaminated feed or other livestock-bird interactions.
The CDC says “the current public health risk is low,” but that's what they also said about the Wuhan Virus.
But when it does make the leap to human hosts, H5N1 is often lethal — out of 26 cases reported since 2022, seven people died. That’s why it’s troubling that H5N1 has been recently discovered to have quietly spread across the country’s (USA) dairy farms, with testing finding genetic material of the virus present in 1 in 5 milk samples across the US. (Pasteurization kills the virus, so milk remains safe to drink. - I will touch base on this subject on another thread soon)
That prevalence suggests that H5N1 is now spreading in mammals — and since cows on dairy farms are in frequent contact with farm workers, it seems likely the virus will have many chances to evolve to spread more easily among humans.
Mia Kim Torchetti, a veterinarian who directs the USDA’s Diagnostic Virology Laboratory at the National Veterinary Services Laboratories in Ames, Iowa, says she had hoped this incursion could be stamped out quickly, but as detections in birds and mammals pile up, “I have rapidly lost hope.”
Though all public health agencies consider the risk of the bird flu spreading widely in people to be low, the outbreak is still reminiscent of the early days of the COVID-19 pandemic.
It has already spilled over to 20 mammalian species.
Torchetti further says,
"We often call the avian influenza virus currently infecting cattle by its nickname, H5N1 bird flu. But its full name is “highly pathogenic avian influenza A H5N1 clade 2.3.4.4b genotype B3.13.”
That specificity denotes the virus’ place in its family tree. Highly pathogenic avian influenza A H5N1 viruses — which are deadly to chickens and related birds — are a huge family tree of bird flu viruses. They all have the H5 form of hemagglutinin, a protein that latches onto host cells so the virus can infect them. The first highly pathogenic avian influenza H5N1 virus was found in 1996. Since then, scientists have documented the tree’s expansion, with some limbs dying off and others making it big. One successful limb of the tree is clade 2.3.4.4b. It has sprouted branches of its own, including genotype B3.13.
Various H5N1s have winged their way around the world after infecting wild birds. A different version crossed the Atlantic in 2014 and caused an outbreak in North American poultry in 2015, but it didn’t take hold, This time is different."
Clade 2.3.4.4 viruses have been infecting poultry and wild birds for several years. But the limb of the tree we’re dealing with now — H5N1 clade 2.3.4.4b — emerged in Europe in October 2020 when two bird flu viruses swapped parts. It came to the Americas in 2021. It has killed more than 90 million birds in the United States since January 2022, including wild birds and commercial poultry and backyard and hobbyist flocks that were culled when the virus was detected.
Influenza viruses are all about the swap meet.
Instead of one long novel, the genetic instruction books of influenza A viruses are more like a series of eight novellas, known as gene segments. Each segment carries one or more of the 11 genes that the virus needs to infect host cells and copy itself. When people, birds or other animals are simultaneously infected with more than one type of influenza virus, the viruses may exchange segments and thus create a new type of virus. This process — called reassortment — has resulted in pandemic strains of flu, including the 1918 influenza pandemic and 2009’s swine flu.
Viruses can’t swap parts willy-nilly. Not all combinations are compatible with each other. But what’s unusual about this clade of H5N1s is that it undergoes reassortment far more often than earlier relatives, Torchetti says.
No one knows exactly where, when and how the virus passed from wild birds into cattle. Cows may have grazed on grass that wild birds carrying the virus pooped on, or the cows may have picked it up through contaminated feed or other livestock-bird interactions.
The CDC says “the current public health risk is low,” but that's what they also said about the Wuhan Virus.
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