The ongoing global avian influenza outbreak that began in 2020 has now spread widely to dairy cows. The features of this outbreak and an assessment of the threat to humans was recently reviewed (Abbasi, J. Bird Flu Outbreak in Dairy Cows Is Widespread, Raising Public Health Concerns. JAMA. 2024;331(21):1789-1791).
As of May 2, 2024, 36 herds have been affected in nine states, and testing found that 1 in 5 retail milk samples analyzed were positive by polymerase chain reaction for the H5N1 influenza strain, which is highly pathogenic for birds. Milk that was pasteurized, however, did not contain live influenza virus and is, therefore, considered to be safe.
Are H5N1 viruses a threat to people? Since 2020, 26 H5N1 cases in people have been reported in eight countries, nearly all after exposure to dead poultry. Fourteen of those cases were severe or critical and seven people died. In the United States, three people have been infected with H5N1; two had direct connections to dairy cows. Although the world’s population has virtually no immunity to this virus, and is therefore highly susceptible to a pandemic, at present a pandemic is unlikely. H5N1 virus does not bind well to cells in the upper respiratory tract. For this reason, human-to-human transmission is extremely rare. Should the H5N1 hemagglutinin evolve to binding to human respiratory cells, a pandemic would be likely. However, H5N1 viruses have been around for more than 100 years and to date have not evolved to reproducing in human respiratory cells.
The ongoing global avian influenza outbreak that began in 2020 has now spread widely to dairy cows. The features of this outbreak and an assessment of the threat to humans was recently reviewed (Abbasi, J. Bird Flu Outbreak in Dairy Cows Is Widespread, Raising Public Health Concerns. JAMA. 2024;331(21):1789-1791).
As of May 2, 2024, 36 herds have been affected in nine states, and testing found that 1 in 5 retail milk samples analyzed were positive by polymerase chain reaction for the H5N1 influenza strain, which is highly pathogenic for birds. Milk that was pasteurized, however, did not contain live influenza virus and is, therefore, considered to be safe.
Are H5N1 viruses a threat to people? Since 2020, 26 H5N1 cases in people have been reported in eight countries, nearly all after exposure to dead poultry. Fourteen of those cases were severe or critical and seven people died. In the United States, three people have been infected with H5N1; two had direct connections to dairy cows. Although the world’s population has virtually no immunity to this virus, and is therefore highly susceptible to a pandemic, at present a pandemic is unlikely. H5N1 virus does not bind well to cells in the upper respiratory tract. For this reason, human-to-human transmission is extremely rare. Should the H5N1 hemagglutinin evolve to binding to human respiratory cells, a pandemic would be likely. However, H5N1 viruses have been around for more than 100 years and to date have not evolved to reproducing in human respiratory cells.