Study suggests pasteurization effectively inactivates highly infectious avian flu in milk

Introduction

In March 2024, an alarming discovery was made in Texas when dairy cows were found to be infected with highly pathogenic avian flu, specifically the H5N1 bird flu. This incident marked the first known case of the virus spreading to cattle, raising significant concerns among health officials and the agricultural community. The Centers for Disease Control and Prevention (CDC) reported that since this initial case, H5N1 has been detected in approximately 200 animals and 3 people across 12 states. The virus’s unexpected presence in dairy cattle prompted immediate scrutiny and a sense of urgency, as it highlighted the potential for cross-species transmission and the associated risks to both animal and human health. Following the discovery of the virus in cattle, raw milk from these infected cows was tested and found to contain the virus, raising questions about the safety of dairy products and the potential for human consumption to facilitate further spread.

This unprecedented situation spurred researchers to investigate whether dairy products could pose a significant health risk to consumers. The detection of H5N1 in raw milk led to concerns that the virus could potentially survive the milk processing pipeline, posing a threat to public health. Erica Spackman, Ph.D., a virologist at the U.S. Department of Agriculture (USDA) in Athens, Georgia, spearheaded a study to determine the extent to which the virus could persist in milk products. She and her collaborators embarked on a comprehensive analysis of nearly 300 milk products from 132 processors to assess the presence and viability of the virus. Their research aimed to establish whether existing sanitation and pasteurization processes were sufficient to eliminate the virus from milk, thereby ensuring the safety of dairy products for consumers. The urgency of this research was underscored by the broader implications of avian flu transmission, not only among migratory birds and domestic poultry but also across a diverse range of animals, including household pets and wildlife, as well as its rare transmission to humans.

Research Objectives

How far is the virus getting through?” asked Erica Spackman, Ph.D., a virologist at the U.S. Department of Agriculture (USDA) in Athens, Georgia. To address this concern, Spackman and her collaborators conducted a comprehensive study. They tested nearly 300 milk products from 132 processors to determine the presence and viability of the virus in dairy products.

Their research aimed to answer this critical question by analyzing the extent to which the H5N1 virus could persist in milk despite standard processing measures. By testing nearly 300 milk products sourced from 132 different processors, the team sought to identify any potential threats posed by the virus in dairy products.

Findings and Results

The researchers found no infectious virus in the samples they tested. These findings were published in the Journal of Virology, a journal of the American Society for Microbiology. “Milk is safe,” Spackman asserted. “Just like bacterial pathogens that occur in milk, or other viruses that could occur in milk, the sanitation processes that are in place are getting rid of the pathogens.”

This conclusion was drawn from rigorous testing and provided significant reassurance about the effectiveness of current sanitation protocols. “Milk is safe,” Spackman asserted. “Just like bacterial pathogens that occur in milk, or other viruses that could occur in milk, the sanitation processes that are in place are getting rid of the pathogens.”

Safety Measures in Milk Processing

The milk processing pipeline includes multiple layers of protection. Microbiological surveillance of milk products is crucial in identifying pathogens. Additionally, stringent measures ensure that milk from cows with mastitis or other disease conditions does not enter the food supply. The heating process during pasteurization serves as another critical step, effectively destroying H5N1 and other common bacterial pathogens, thus ensuring the safety of dairy products for consumers.

Broader Impact of Bird Flu

Bird flu primarily infects and spreads among migratory birds and can be transmitted to domestic poultry. However, the virus has also been detected in other animals, including cats, dogs, juvenile goats, a polar bear in Alaska, and elephant and fur seals in Antarctica. The discovery of H5N1 on dairy farms in March was a significant surprise, as the virus had never been found in dairy cattle before.

Investigation of Raw Milk

Following the discovery of the virus in dairy cattle, diagnostic testing revealed that an infectious form of the virus was present in raw milk. This suggested that the virus could pass from cow to milk. Consequently, the U.S. Food and Drug Administration (FDA) and the USDA initiated an investigation to determine whether pasteurization effectively eliminates the risks posed to consumers.

Detailed Study on Pasteurized Milk

Between April 18 and April 22, 2024, researchers conducted a thorough investigation using real-time PCR to examine 297 samples of pasteurized retail milk products, encompassing 23 different types collected from 17 states across the United States. This comprehensive sampling aimed to assess the presence and potential viability of the H5N1 virus in dairy products after pasteurization. Erica Spackman, Ph.D., from the U.S. Department of Agriculture (USDA), explained their approach: “We did a viability assay to detect live virus and went as sensitive as we could to get even the least little bit of virus, but couldn’t detect anything.”

Despite detecting viral genetic material in 20% of the samples through PCR, the crucial finding was that the virus was entirely inactivated. This outcome underscores the robustness of pasteurization in eliminating the threat posed by H5N1 and similar pathogens in milk products. Spackman’s team’s meticulous analysis and rigorous testing provide strong evidence supporting the safety of pasteurized dairy products. These results not only validate current safety protocols but also reinforce public confidence in the effectiveness of pasteurization against emerging viral threats in the dairy industry. The study’s findings are pivotal for regulatory agencies and health authorities in ensuring continued consumer safety amid evolving challenges in food safety and public health.

Conclusion

Spackman emphasized that the new findings provide reassurance. “What we have been doing—pasteurization—is keeping us safe from what we don’t know about,” she concluded. This study underscores the effectiveness of pasteurization in ensuring the safety of milk and dairy products, even in the face of new and unexpected threats like H5N1 bird flu. These findings highlight the critical role of pasteurization as a reliable safeguard against emerging pathogens, reaffirming its importance in maintaining the safety and integrity of the dairy supply chain.