In recent research , a study led by Hugo Francisco de Souza reviewed the effectiveness of pasteurization in inactivating influenza viruses in milk. This study reconfirms the importance of pasteurization in ensuring the safety of dairy products for consumers by preventing the transmission of viruses like influenza, including H5N1, and highlights the critical role this process plays in public health.
Influenza Viruses in Raw Milk
Influenza viruses are known to cause a variety of diseases, with the most notable strains being H5N1, a highly pathogenic avian influenza virus (HPAIV), which can infect a variety of mammals. There have been several documented cases of influenza viruses, particularly H5N1, being shed in milk from infected cows, posing a potential risk of transmission to humans and other animals. This is especially concerning since, while influenza typically spreads via respiratory or fecal-oral routes, milk can carry infectious viruses at startlingly high titers, leading to concerns about public health safety.
In particular, the H5N1 virus has caused massive outbreaks among poultry and mammals alike, and recent cases of bovine infection in the U.S. have raised alarms. The discovery that infected cows could shed high levels of influenza virus in their milk has underscored the need for effective measures to eliminate these risks in the dairy industry.
The Role of Pasteurization
Pasteurization, named after Louis Pasteur, the French microbiologist who pioneered the method in the 19th century, involves heating liquids to a specific temperature to kill harmful microorganisms, including bacteria and viruses, without compromising the quality of the product. This method has been widely used to ensure the safety of milk and other dairy products. Traditionally, pasteurization was primarily concerned with bacterial pathogens, such as Mycobacterium tuberculosis and Brucella, that are known to thrive in raw milk. However, with the advent of new concerns about viral pathogens, particularly influenza viruses, there has been increased scrutiny of whether pasteurization can also deactivate these viruses in milk.
The study evaluated various strains of influenza viruses, including H5N1, H5N2, and H5N3, as well as influenza D virus (IDV). These viruses are known to infect both poultry and mammals and could pose a serious health risk to consumers if transmitted through milk. The study used two common methods of pasteurization: Low-Temperature Long Time (LTLT) and High-Temperature Short Time (HTST), both of which are standard procedures used globally to ensure milk safety.
Research Methods
The research team used a combination of laboratory-grown and naturally sourced milk to assess the effectiveness of pasteurization at inactivating influenza viruses. The milk used in the experiments was sourced from supermarkets in the UK and the University of Edinburgh, ensuring a diverse sample for testing. The viruses were mixed with milk and subjected to pasteurization at either 63°C (LTLT) for 30 minutes or 72°C (HTST) for 15 seconds, the typical temperatures used in milk pasteurization processes.
Once the milk was pasteurized, the researchers assessed the viral infectivity through immunocytochemistry experiments using Madin-Darby Canine Kidney (MDCK) cells, which are commonly used to test the infectivity of viruses. The assays confirmed that, across the board, influenza viruses, including H5N1, H5N2, H5N3, and IDV, were effectively inactivated by the pasteurization process. Viral infectivity dropped significantly in just a matter of seconds, much earlier than the full pasteurization process took, underscoring the rapid efficacy of the heat treatment.
The study found that both the LTLT (63°C for 30 minutes) and HTST (72°C for 15 seconds) methods resulted in the rapid inactivation of influenza viruses, including several strains of the H5 family and IDV. These findings were consistent across different types of milk, including whole, semi-skimmed, and skimmed milk. The viral infectivity of the tested samples decreased substantially, often by orders of magnitude, even before the full pasteurization time was reached.
This study also found that the pasteurization process inactivated the viruses even when viral genetic material was still detectable. While the presence of viral RNA was confirmed in some samples, it was not infectious. This is a key finding, as it suggests that pasteurized milk, even if it contains trace amounts of viral material, is safe to consume and poses no significant risk of transmission to humans.
The results are of immense importance, reinforcing the safety of milk that undergoes pasteurization, and further justifying the global practice of pasteurizing milk before it reaches consumers.
Implications for Public Health
The study also has critical implications for public health, especially in light of the recent avian influenza outbreaks in American cattle. The detection of high levels of influenza virus in cow’s milk during these outbreaks raised significant concerns about the potential for human infections through the consumption of raw milk.
The findings of this study underscore the importance of ensuring that milk and dairy products are properly pasteurized before consumption. While raw milk may still carry infectious influenza viruses, pasteurization effectively neutralizes this risk. Therefore, public health authorities continue to recommend the consumption of pasteurized milk to prevent any potential transmission of pathogens, including viruses such as H5N1.
Furthermore, the study highlights that pasteurization methods are effective regardless of the fat content in the milk. Whether it is whole, semi-skimmed, or skimmed milk, pasteurization provides a uniform level of protection against viral transmission, ensuring the safety of all types of dairy products.
This study provides strong evidence supporting the effectiveness of pasteurization in inactivating influenza viruses in milk. The research confirms that the widely used pasteurization methods, both LTLT and HTST, are sufficient to render milk safe from influenza viruses, including H5N1, H5N2, H5N3, and IDV. While raw milk continues to pose a health risk, pasteurized milk remains a safe and reliable source of nutrition for consumers.
Given the increasing concerns about viral transmission through milk, particularly in light of recent outbreaks in cattle, this study provides a critical reminder of the importance of pasteurization in safeguarding public health. It also highlights the continued need for rigorous quality control in dairy production to ensure that all milk products are properly heat-treated.
As this study shows, pasteurization not only protects consumers from bacterial pathogens but also from potentially dangerous viral infections. With the world continuing to face emerging infectious disease threats, pasteurization remains a vital public health tool for ensuring the safety and security of food products.