Bird flu survived pasteurization of heavily infected milk: study

In raw milk samples mixed with high levels of the bird flu, small amounts of the virus still remained after going through a standard pasteurization process, researchers discovered recently.

The findings reflected experimental conditions in a laboratory and should not be used to draw any conclusions about the safety of the U.S. milk supply, according to the authors of the study from researchers with the National Institutes of Health. 

The research was published in the New England Journal of Medicine. As more information comes to light about the virus, countries around the world are looking to step up their vaccination efforts to prevent what could be another pandemic-like event for humans.

With limited data available regarding the susceptibility of bird flu in milk after pasteurization, researchers sought to experiment with different time intervals of heat treatment on infected raw milk at 63 degrees Celsius and 72 C (or between 145.4 degrees Fahrenheit and 161.6 F) — the temperatures most common in commercial dairy pasteurization processes. 

While pasteurization rapidly reduced the amount of bird flu virus in the samples, a small amount was found in a third of the samples after up to 20 seconds of heat treatment at 72 C.

“This finding indicates the potential for a relatively small but detectable quantity of H5N1 virus to remain infectious in milk after 15 seconds at 72 C if the initial virus levels were sufficiently high,” the authors said in the study. 

Despite the potentially alarming results, the researchers underscored that their study has limitations. Raw milk from cows infected with the virus may react differently to pasteurization compared to the experimental samples, which were spiked with H5N1 isolated from the lungs of a dead mountain lion in Montana.

To date, the U.S. Food and Drug Administration has said the commercial milk supply is safe for human consumption, and the department has conducted tests on retail dairy products that all came back negative for bird flu. 

The H5N1 strain of bird flu has killed or resulted in the culling of hundreds of millions of poultry around the world in recent years, with more cases spreading to mammals and in some cases humans.

Recently, a 59-year-old man from Mexico contracted a rare case of the H5N2 bird flu virus, which had never before been confirmed in a human, and died in April due to other health complications, according to the World Health Organization. Earlier this year, a toddler in Australia tested positive for H5N1 after a brief trip to India and recovered following treatment.

Finland will begin offering bird flu inoculations for workers exposed to the virus as soon as next week, Reuters reported, making it the first country in the world to do so. Although no humans in the Nordic country have contracted the virus, the country is ready to deploy the vaccine given the transmission risks of its fur farms. 

In the U.S., bird flu detections among dairy cows have surged in Idaho, Iowa and Colorado, with each state reporting more than 10 infected herds in the past 30 days, according to the Department of Agriculture’s online tracker as of June 21. Three farm workers have contracted the virus after exposure to infected dairy cows in Texas and Michigan since the outbreak emerged in late March.