Raw milk has always been a risk when it comes to its ability to harbour harmful pathogens. These include viruses, such as the influenza (flu) virus. Most people consider raw milk to be risky when it comes to bacterial infections. However, new research demonstrates that the flu virus survives in raw milk for longer periods even under refrigeration. Here we explore the findings of the science about how long the influenza virus survives in raw milk, what it means in terms of public health consequences and what this all means to those intending to consume unpasteurised milk.
How long can the flu virus survive in refrigerated raw milk?
Scientific research indicates that the flu virus can survive in refrigerated raw milk for five days. A study by Stanford University researchers showed that the H1N1 strain of the flu virus, which is the common seasonal flu strain, can retain its infectivity in raw cow’s milk even at the usual refrigeration temperatures of 4°C or 39.2°F.
In this experiment, the virus was added to raw milk and refrigerated to mimic normal household storage conditions. The researchers found that even after five days of refrigeration, the virus was still able to infect cells. The persistence of the flu virus in milk was a concern due to the possibility of transmitting it, especially to raw milk consumers, which does not undergo pasteurisation that would typically kill such viruses.
Why does the flu virus survive in raw milk?
Survival of the flu virus in raw milk is possible due to the characteristics of the virus itself and the properties of raw milk. Viruses such as influenza are stable at cold temperatures, and that is why refrigeration prolongs their life span. The viral particles remain viable in refrigeration because cold does not immediately degrade or inactivate the viruses.
However, raw milk carries proteins, fats, and sugars that are capable of preserving the viruses. Pasteurisation kills harmful microbes when they are exposed to heat, but it provides an environment supporting survival for some pathogens by just keeping the raw milk. High levels of protein in the milk could also offer a more stable environment for the influenza virus than other liquids.
Does pasteurisation deactivate the flu virus?
Yes, pasteurisation does efficiently inactivate the flu virus. The basic principle of pasteurisation involves heating milk to a given temperature, typically 71.7°C for 15 seconds, to kill all harmful bacteria and viruses. From scientific studies, we see that pasteurisation does not only kill harmful bacteria such as Salmonella and E. coli but also viruses such as the influenza virus.
At these temperatures, the heat cannot allow the survival of the flu virus when milk is raw. Heat works to denature the proteins viruses require to remain intact in host cells. It results in a reduction of the potential transfer of the flu virus from individuals who consume milk.
What do health authorities recommend?
Health authorities around the world, including the UK’s Food Standards Agency (FSA) and the US Centers for Disease Control and Prevention (CDC), have advised against drinking raw milk. The authorities note that raw milk may be contaminated with harmful bacteria and viruses and caution consumers that pasteurisation is the only surefire way of preventing foodborne illnesses.
According to reports by the CDC, consumers who consume unpasteurised milk face a 150 times higher risk of experiencing foodborne illness compared to a person who consumes pasteurised milk. The causative agents include bacteria and viruses such as the influenza virus. Public health professionals remain convinced that pasteurised milk is safe and nutritionally appropriate for the majority of people since it protects against possible deadly infections.
Conclusion
From the scientific evidence that is present, it is evident that the flu virus can survive for up to 5 days in refrigerated raw milk. This, in turn, may seem worrying; however, it is essential to remember that pasteurisation renders the flu virus ineffective and hence reduces the risk of contamination of the milk.
Given the dangers that come with raw milk consumption, which include bacterial infections, among others, and transmission of viruses, most people should choose pasteurised milk. In this regard, public health agencies across the globe advise against consuming raw milk because it poses the risk of carrying pathogens harmful to human health, including the flu virus.
In summary, although the flu virus may survive in raw milk for several days, pasteurisation is a simple and effective way to eliminate this risk. For those who are concerned about milk safety, it is always best to opt for pasteurised milk, as it significantly reduces the risk of both bacterial and viral contamination, thus making the product safer for consumption.
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