Bird Flu Was Circulating 4 Months Before Detection

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May 3, 2024 – Bird flu was circulating in U.S. dairy cows for at least 4 months before it was discovered and confirmed to be the disease-causing H5N1 virus, according to an analysis of data by the U.S. Department of Agriculture’s Animal Disease Center.

It appears the virus moved from an infected bird to a dairy cow late last year or early this year, according to the study published on the bioRxiv server on Wednesday. 

The new analysis is another indication the bird flu strain has spread more widely than first believed. The strain has been found in cattle with no known connections to other infected herds, suggesting “there are affected herds that have not yet been identified,” the study said.

The researchers came to their conclusions after analyzing a dump of genomic data by the USDA into a public repository on April 21. Researchers were concerned the data wasn’t released until almost 4 weeks after the March 25 announcement of the outbreak, according to Nature.

“It’s good news that there’s only been one jump that we can discern so far. But bad news, in many ways that it has been spreading for probably several months already,” said Michael Worobey, PhD, an evolutionary biologist at the University of Arizona in Tucson, according to Nature.

Since the USDA announced the outbreak in a Texas dairy heard, infections have been found in about three dozen herds in Colorado, Idaho, Kansas, Michigan, New Mexico, North Carolina, Ohio, South Dakota, and Texas.

Last week, the FDA said a nationwide survey found traces of the bird flu virus in 1 in 5 retail samples of pasteurized milk. But those tests don’t necessarily represent actual viruses, health experts have said.

The FDA says the nation’s milk supply is safe because of the pasteurization process and because of “the diversion and destruction of milk from sick cows.”