Meat from condemned dairy cow tested positive for H5N1 flu virus but did not enter food supply, USDA says

Meat from a dairy cow that was culled from its herd and sent to slaughter has tested positive for traces of the H5N1 bird flu virus, the US Department of Agriculture announced Friday, but no meat from the cow entered the food supply.

The USDA said viral particles of H5N1 were detected during testing of various tissues, including samples from the diaphragm muscle, which sits below the lungs. The testing was done as a standard part of the food inspection process, the USDA said.

Infectious disease experts around the world have been on alert since the USDA announced March 25 that a dairy cow tested positive for H5N1 influenza.

H5N1 is a highly pathogenic form of bird flu that scientists have watched closely since it was detected in 1996. It has decimated wild bird populations and poultry flocks but only sporadically infects humans. When it does, it can be fatal: About half of the roughly 900 people known to be infected around the world over the past two decades have died.

In the past two years, the virus has changed and begun to infect a growing assortment of mammals. Experts never expected the virus to show up in cows, as it was thought that they didn’t have the right receptors on their cells to catch A-strain flu viruses – but it turns out they do.

In this outbreak, the virus has mostly been showing up in the milk of dairy cows and causing mastitis, or an infection of the mammary gland. Cows stop producing as much milk, but they generally recover after a few weeks.

Two US farmworkers are known to have tested positive in conjunction with the ongoing dairy cow outbreak. In both cases, the virus infected their eyes, causing redness and swelling, but they recovered.

Finding a cow that tested positive for H5N1 postmortem, after systemic disease, suggests that some sick animals are going undetected. It also suggests that the owners may not have tested the animal before its slaughter and that other cows in the herd may be infected.

The USDA said the dead cow tested positive for H5N1 on May 22. It has notified the owners and is tracing the animal to the herd it came from to get more information, the agency said.

The USDA says samples taken from 95 other cows that were culled and condemned for illness tested negative for the virus as of May 22, and testing is underway on about a dozen more samples. The test the USDA used, which is called polymerase chain reaction testing or PCR, identified genetic material from H5N1 virus, but it could not determine whether that material was infectious and could have made someone sick.

Earlier tests on samples of ground beef using a different virus as a stand-in for H5N1 found that the virus was killed when the burgers were cooked to at least 145 degrees Fahrenheit, or medium. Cooking burgers to rare, a temperature of 120 degrees, substantially reduced levels of active virus but did not kill it all. The USDA already recommends that burgers be cooked to an internal temperature of 160 degrees to kill dangerous pathogens such as salmonella and E. coli.

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