The researchers collected milk samples from cows in New Mexico that had been infected with HPAI H5N1. The samples contained a total of 8 different HPAI H5N1 viruses.
The team first heated infected milk at 63°C (145°F) for 5, 10, 20 or 30 minutes. All these experiments reduced the virus to levels that couldn’t be detected by a standard test. When using higher heat—72°C (161°F)—for briefer periods of 5, 10, 15, 20 or 30 seconds, levels of the virus were reduced but not eliminated.
These temperatures mimicked those used in milk pasteurization. The experiments suggest that heat may be able to neutralize HPAI H5N1 in dairy milk. However, additional work is needed to directly test whether industrial pasteurization methods kill the virus.
The researchers also stored raw milk infected with H5N1 in refrigerated conditions (4°C, or 39°F) for 5 weeks and found only a small decline in virus levels. This shows that the virus can likely remain infectious in raw milk when maintained at refrigerated temperatures.
Finally, the scientists fed milk from a cow infected with an HPAI H5N1 strain to five mice. All animals showed signs of illness by 1 day after exposure to the milk. When the team examined the animals’ organs 4 days after infection, they found HPAI H5N1 throughout their bodies, including the nasal passages and lungs. The results suggest that consumption of raw milk may pose a risk for H5N1 infection.
“We must emphasize that the conditions used in our laboratory study are not identical to the large-scale industrial treatment of raw milk,” notes lead researcher Dr. Yoshihiro Kawaoka of the University of Wisconsin-Madison. “It’s important to remember that our heat-treatment findings may not perfectly translate to real-world conditions.” However, to date, there hasn’t been evidence that commercially pasteurized milk poses an infection risk.
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