The recent discovery of bird flu fragments in cow milk on U.S. grocery store shelves has sparked new concerns about the potential health risks to humans. The virus, known as highly pathogenic avian influenza H5N1, has been spreading between cattle for months. This revelation has led to pressing questions: Is the virus adapting to infect mammals more effectively? Can people contract bird flu by consuming milk from infected cows?
Assessing the Risk
Is there a real threat from cow milk?
On April 23, the U.S. Food and Drug Administration (FDA) reported that genetic fragments of H5N1 had been detected in milk. Preliminary findings suggest that about 20% of the tested milk samples contained traces of the virus’s RNA. Samples from regions with infected dairy herds showed a higher likelihood of testing positive.
Despite these findings, experts like Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota, assure that pasteurized milk remains safe. “Pasteurization effectively kills virus particles, so there is no significant public health concern regarding the ingestion of infected material,” Osterholm explains.
Why Pasteurization Matters
Pasteurization involves heating milk to a temperature high enough to kill bacteria and viruses. This process has historically proven effective against various pathogens, including E. coli and Listeria. H5N1, an enveloped virus, is particularly susceptible to this heat treatment, making pasteurized milk safe for consumption.
While the FDA acknowledges that specific studies on pasteurizing milk with H5N1 are lacking, related studies on egg pasteurization have demonstrated the virus’s inactivation. Consequently, the FDA advises against drinking raw milk, which has not undergone pasteurization, as it could pose health risks.
Can Humans Contract Bird Flu from Milk?
Decades of research suggest that humans are unlikely to contract bird flu through ingestion. Influenza viruses typically require specific receptors to infect cells, which are found in the upper respiratory tract and eyes of humans, not in the digestive system. This explains why cases of human infection from consuming infected animals or their products are extremely rare.
However, humans can contract the virus through direct contact with infected animals or their secretions. For instance, a Texas farm worker recently developed conjunctivitis after exposure to infected cows.
Current Spread of Bird Flu
The U.S. Department of Agriculture (USDA) first identified bird flu in dairy cattle in Kansas and Texas in March 2024. Since then, the virus has spread to dairy cows in eight states and poultry in five states. Genetic analyses suggest that H5N1 may have jumped from birds to cattle in late 2023 and has since spread among cows.
These findings indicate that bird flu in cattle might be more widespread than previously identified. Although the risk to human health remains low, experts emphasize the need for continued surveillance and testing.
Health Implications for Cattle and Other Animals
Infected cattle typically exhibit mild symptoms such as reduced appetite, lower milk production, and fatigue. However, the virus can also be asymptomatic in some cows. The USDA recently found lung tissue from an asymptomatic cow testing positive for H5N1.
Additionally, the virus has been detected in cats on dairy farms in Texas, Poland, South Korea, and France, with at least one fatality reported. For poultry, H5N1 can be devastating, rapidly decimating entire flocks.
Potential for Human Adaptation
While the H5N1 virus has not yet developed the ability to spread easily from person to person, experts remain vigilant. Reassortment, a process where flu viruses exchange genetic material, could potentially lead to a strain capable of human-to-human transmission.
“Any transmission from bird populations to mammals is cause for concern,” says environmental epidemiologist Meghan Davis of Johns Hopkins Bloomberg School of Public Health. “Protective measures for those in contact with infected animals are crucial to prevent possible infections.”
Although the detection of bird flu fragments in cow milk has raised alarms, pasteurization effectively neutralizes the threat, ensuring that milk remains safe to drink. Continuous monitoring and preventive measures are essential to mitigate the risks associated with H5N1. Public health officials emphasize the importance of avoiding raw milk and ensuring thorough cooking of meat products to prevent potential infections.
