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Bird flu has been circulating among cows for months, analysis shows

The H5N1 subtype of avian influenza had been circulating in cows for months before being detected in late March, according to a new preprint analysis released by U.S. Department of Agriculture scientists on Wednesday.

The H5N1 subvariant of bird flu has been increasingly reported in livestock in recent weeks, with 36 cases reported in nine states since March 25.

According to the analysis, which has not yet been peer-reviewed, veterinarians began noticing unexplained reductions in milk production, a decrease in feed consumption and changes in milk quality in late January, leading to tests that found the virus in the animals’ milk and nasal swabs. cows.

The scientists noted that the same genotype of the virus has been found in cattle herds with no known links to each other, indicating that there are affected herds that have not yet been found.

The scientists also found that, considering that all cattle appear to have a descendant type of virus of the same type, it is likely that there was a single contagion event when the virus infected cattle and then began to spread among cattle. According to an analysis by scientists, it is estimated that the first infection occurred in early December.

A sign on the edge of an exclusion zone warns of the closure of a footpath following an outbreak of bird flu in the town of Upham, southern England, February 3, 2015. (Credit: REUTERS/PETER NICHOLLS)

Additionally, scientists found that there were five incidents in which the virus was transmitted from livestock to poultry, one case of transmission from a cow to a raccoon, two cases of cats infected by cows, and three cases of wild birds infected by cows.

The analysis also found several cases of mutations in the virus associated with increased virulence and transmission, as well as mutations that allow the virus to be better adapted to infect mammals, although all of these mutations were found infrequently in the cattle analyzed. However, scientists noted that as the virus spreads further, it will give these mutations more chances to spread and develop, and emphasized that these should be monitored to detect whether or not they increase in frequency.

Outbreaks of avian influenza among cattle and other animals on dairy farms have been reported since March.

Outbreaks may also have occurred among farm workers

Last month, a person who was exposed to infected cows in Texas was found to be infected with the H5N1 subtype, with conjunctivitis being his only symptom. The infected person was treated with an antiviral flu medication and recovered.

While that person remains the only confirmed case of infection among dairy workers, health officials have expressed concern that there may be more infected farmworkers who are not getting tested.

Dr. Barb Petersen, a dairy veterinarian in Amarillo, Texas, told NBC last week that several dairy workers had fallen ill with “classic flu-like symptoms,” including high fever, night sweats, chills, lower back pain, stomach upset, vomiting and diarrhea. They also suffered from conjunctivitis. These workers were not tested for the H5N1 virus, so it is unclear whether they were infected with bird flu or another disease.

Petersen told Fortune on Wednesday that he “had people who never missed work, missed work” on affected farms due to illness.

Dr. Keith Poulsen, director of the Wisconsin Veterinary Diagnostic Laboratory, told NBC last week that he had also heard reports of flu-like illnesses on affected dairy farms.

Gregory Gray, an infectious disease epidemiologist at the University of Texas Medical Branch in Galveston, told NPR on Thursday that he suspects there are at least several cases of farmworkers infected with the virus, as some workers sought medical attention for cases.” similar to influenza. diseases and conjunctivitis” at the same time that H5N1 was spreading on dairy farms.

In total, about two dozen people have been tested since the outbreak began among livestock, Dr. Demetre Daskalakis, a respiratory diseases official at the CDC, said Wednesday, according to Fortune.

Health officials have called for more widespread testing, noting that there is a stigma around getting tested among many farmworkers, in part because of concerns that it will affect their farms. However, without widespread testing, it will be difficult for health officials and scientists to track the spread of the virus and monitor any evolution in its ability to spread or cause serious illness.

Meanwhile, the USDA announced Wednesday that testing on retail ground beef had revealed that all samples had tested negative, reaffirming that the commercial beef supply is safe for consumers. The USDA is conducting more testing on muscle samples from slaughterhouses and to see if cooking beef containing the virus is effective in killing it.

Additionally, the FDA announced Wednesday that it had found that pasteurization is effective in killing H5N1. No live, infectious virus was found in any retail dairy product samples.

Bird flu outbreaks continue among mammals

Outbreaks of avian influenza in mammals have been increasingly reported as the virus continued to spread around the world in recent years.

Since 2021, Europe and the Americas have suffered a near-continuous outbreak of H5N1 bird flu, which has been described as “the largest ever recorded” on all three continents. The virus has affected tens of millions of birds and thousands of mammals around the world. Outbreaks of the virus have also become more common in Africa and Asia over the past year and have even spread to Antarctica in recent months.

The World Organization for Animal Health (WOAH) noted in March that, while estimates vary, around 485 species of birds and 37 species of mammals have been infected with avian influenza since 2021. Only the Pacific Islands, Australia and New Zealand They have escaped the epidemic. virus.

“Wildlife loss on the current scale presents an unprecedented risk of wildlife population collapse, creating an ecological crisis,” WOAH noted.