According to recent reports in the US media, a highly pathogenic avian influenza virus has been quietly circulating in US cattle herds for months based on a preliminary analysis of genomic data from dairy cows in the United States. The outbreak is likely to have been transmitted to cows by infected birds, and the outbreak could have occurred in late December or early January this year. This means that the avian influenza virus has been circulating for a long time and has not been detected before, and it also indicates that the number of cattle infected with avian influenza in the United States and even neighboring countries may be higher than currently reported.
The U.S. Department of Agriculture (USDA) recently transferred genomic data to a public database, and researchers quickly summarized and analyzed the genomic data to reach the above conclusions, Nature said on April 27. But to the disappointment of scientists, the USDA's publicly released data lacked critical information that could shed light on the origins and evolution of the outbreak. And the fact that the genomic data was released nearly four weeks after the bird flu outbreak became public is a concern to the researchers.
U.S. federal government officials announced on March 25 that a highly pathogenic strain of avian influenza had been detected in dairy cows. Since then, the USDA has confirmed that 34 dairy herds in nine U.S. states are infected with the virus, named H5N1. In late March and early April, the USDA published a small number of viral sequences and a human case sequence sampled from dairy cows in Texas on the widely used GISAID database.
Gene fragments of avian influenza virus have been detected in milk from outbreak areas
On April 21, the USDA released additional sequencing data on the Sequence Read Archive (SRA) maintained by NCBI. Karthik Gangavarapu, a computational biologist at the Scripps Institute in La Jolla, who processes the raw data, said the latest data upload includes about 10 kigabytes of sequencing information from 239 animals, including cows, chickens and cats.
Science News magazine reported that on April 23, the U.S. Food and Drug Administration announced that a genetic fragment of avian influenza had been found in milk on the market. The agency announced on April 25 that preliminary results showed that about 1 in 5 samples contained RNA fragments of the virus. Samples taken from areas where infected cows were found were more likely to detect avian influenza viruses than samples from no infected herds.
Analysis of the genome suggests that this wave of bovine avian influenza may have started in December 2023 or was introduced by wild birds in early January this year. "So far, we've only found one host jump, which is good news. Michael Worobey, an evolutionary biologist at the University of Arizona in Tucson, analyzed the genome.
Louise Moncla, an evolutionary virologist at the University of Pennsylvania in Philadelphia, who studied the genomic data, said, "The virus obviously spreads from cow to cow in some way. ”
The H5N1 avian influenza virus has been quietly circulating in U.S. cattle herds for months
Nelson, who is analyzing the data, said she was most surprised by the fact that the virus that infects cattle has seen multiple genetic mutations, suggesting that the virus has evolved for months. Among the mutations, she said, there was a change in the protein part of the virus that scientists thought could be related to its adaptation to spread among mammals.
"The data also shows that the virus occasionally jumps back from infected cows back to birds and cats," Nelson said, "and it's a multi-host outbreak." ”
Eric Bortz, a virologist at the University of Alaska at Anchorage, said that based on available data, a host jump a few months ago was "the most reliable conclusion." He said it was unclear what percentage of infected cows the samples represented.
The H5N1 avian influenza virus has been quietly circulating in U.S. cattle herds for months
Tulio de Oliveira, a bioinformatician at Stellenbosch University in South Africa, said speed of detection and control is especially important for respiratory pathogens that have the potential to trigger a pandemic. The outbreak of bovine avian influenza is not expected to spread the virus to humans, but researchers remain vigilant.
Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota, said: "At first glance, this should seem like a major threat to human health. However, the pasteurization process is actually very effective at killing these viruses, so we don't have to worry about ingesting infectious substances. ”
However, the U.S. Food and Drug Administration said in an April 23 statement that it had not directly tested the ability of milk pasteurization to kill the avian flu virus because the H5N1 virus had only recently been detected in cattle. Studies have shown that egg pasteurization is cooler than milk pasteurization and can inactivate the virus.
And Martha Nelson, a genomic epidemiologist at the National Center for Biotechnology Information (NCBI) in Bethesda, Maryland, USA, urged effective action as soon as possible, saying, "The sooner you have data in response to an outbreak, the sooner you can act." He added that with each passing week, the window to control the outbreak narrowed. Yangtze Evening News/Purple Cow News reporter Song Shifeng
Proofread by Xu Heng