A “small but detectable quantity” of infectious H5N1 bird flu virus can survive a common approach to pasteurising milk, according to new research co-authored by scientists at the National Institutes of Health (NIH). This finding has sparked concern and raised questions about the potential impact of the H5N1 virus on humans and the food supply.

New Research Findings

The research, published in The New England Journal of Medicine, was based on experiments conducted in NIH labs. Notably, this does not mean that the infectious H5N1 virus has been found in milk from grocery stores. So far, officials have not detected infectious virus in supermarket milk samples.

The study’s findings come as authorities continue identifying newly infected herds amid this year’s unprecedented outbreak of H5N1 bird flu in dairy cattle. Infections have been detected in cows across farms in at least a dozen states, with most positive tests coming from raw milk samples teeming with the virus. 

Authorities have urged states to curb raw milk sales that could spread the virus and have warned consumers against drinking raw milk. “The study reflected experimental conditions and should not be used to draw any conclusions about the safety of the U.S. milk supply,” an FDA spokesperson said.

In commercial dairy processing, milk from infectious cows is likely mixed with milk from healthy cows, diluting the virus and reducing the risk of it surviving. Pasteurisation, which involves heating milk at high temperatures for some time to kill contaminants, is effective in reducing this risk.

Experimental Laboratory Conditions

The NIH study looked at two approaches to pasteurisation on milk with concentrations of the H5N1 virus added at levels similar to those in some highly infectious cows. One method heated the milk to 72 degrees Celsius (about 161 degrees Fahrenheit) for 15 seconds, a widely used technique in the dairy industry. 

This method yielded milk with “minute amounts of infectious virus,” according to Vincent Munster, chief of the virus ecology unit at the National Institute of Allergy and Infectious Diseases.

The second pasteurisation approach, which involved heating the milk for half an hour at 63 degrees Celsius, was more effective, rendering the virus undetectable within minutes, long before the pasteurisation process was complete.

Implications for Public Health

Despite the findings, the FDA maintains that the commercial milk supply is safe. Pasteurisation processes used by U.S. dairy companies are effective at killing H5N1, and many companies use temperatures more significantly than the minimum standards, providing an additional safety margin.

However, the study highlights the importance of ensuring that pasteurisation processes are robust enough to handle potential viral contamination. This is particularly relevant given the ongoing outbreak of H5N1 among dairy cattle and other animals.

The Broader Impact of H5N1 on Human

The H5N1 virus, also known as avian influenza A, has been responsible for killing millions of wild birds and causing sporadic outbreaks among poultry. 

Recently, there has been a multistate outbreak among cows in the United States, with three dairy workers infected, marking the first cow-to-human transmissions. While these cases have not resulted in person-to-person transmission, the potential for the virus to spread among humans remains a concern. 

The Centers for Disease Control and Prevention (CDC) has categorized the risk to the general public as “low” but continues to monitor the situation closely.

What Is H5N1?

H5N1 is a type of influenza A virus primarily affecting birds. It was first identified in geese in China in 1996 and in humans in Hong Kong the following year. 

A new variant, Highly Pathogenic Avian Influenza (HPAI) H5N1, was detected in wild birds in Europe in 2020 and has since spread to the United States and Canada.

Current Human Cases and Concerns

To date, there have been four human cases of H5N1 in the U.S., all involving farm workers exposed to infected animals. The most recent case involved a dairy worker in Michigan who experienced typical flu-like symptoms. These cases underscore the need for continued vigilance and preventive measures.

Symptoms and Testing

Symptoms of H5N1 infection can range from mild flu-like illness to severe respiratory issues. Currently, there is no publicly available test for H5N1, and dedicated testing is only performed at public health laboratories.

Food Safety and the Role of Pasteurization

The FDA has conducted extensive testing of retail dairy products, confirming that pasteurization effectively kills the H5N1 virus. However, the agency advises against consuming raw milk due to the risk of contamination.

The ongoing research and monitoring efforts by NIH, FDA, and CDC are critical in understanding and mitigating the risks associated with H5N1. 

While the current risk to the general public remains low, continued vigilance and adherence to safety guidelines are essential to prevent the spread of this virus. For the latest information on H5N1 and other public health concerns, visit the CDC and WHO websites.

The information is taken from CBS News and The Conversation