The recent detection of H5N1 in cattle is worrisome, but pasteurization exists for exactly this reason. Just don’t drink raw milk.
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The recent reports from the United States about H5N1 being detected in the milk supply is concerning. It means that avian influenza has spread to dairy cattle and was probably spreading undetected since late December, far before the first reported case in March. It doesn’t mean that the milk supply is unsafe.
The worry with H5N1 — a.k.a. avian influenza, a.k.a. bird flu — is its potential to infect humans. How much of a concern this should be is uncertain. There have been a relatively small number of human cases of H5N1 since 1997. Most cases were bird-to-human and occurred in people who were in close contact with infected birds, especially poultry. Human-to-human transmission has occurred, but not in a sustained fashion. H5N1 still primarily infects birds. It hasn’t yet gained the ability to spread easily among humans.
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But its recent detection in cattle is worrisome. If it can now easily infect cows and other mammals, it may soon gain the ability to more easily infect and, more importantly, spread directly among humans.
But a lot has to happen before that becomes a reality, and it’s not clear how much of a concern to human health an H5N1 human outbreak would be. The human cases to date have been quite severe on the whole, but there has been a spectrum of illness with mild cases too.
We also have tools at our disposal to combat any possible pandemic. We have vaccines against influenza, and specifically against H5N1, and also antivirals to treat severe cases. Maybe H5N1 won’t jump to humans, but emergency preparedness is about preparing for a possible emergency while also hoping the plan never has to be put in place. We practise fire drills in schools not because we expect schools to burn down, but because we want to be ready on the off chance they do.
The recent reports about the detection of H5N1 in cows and commercially available milk is obviously worrying. But we pasteurize our milk for exactly this reason. While genetic traces of the virus were found in milk using PCR testing, there was no live virus capable of causing an infection. That means that pasteurization was effective at inactivating the virus. So the milk supply is safe and you don’t need to worry about transmission of the virus from dairy products. Unless you drink raw milk.
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Every so often raw milk becomes popular as a health fad with people claiming it’s healthier than pasteurized milk. Some claim pasteurization is dangerous, which it obviously isn’t since it basically just amounts to heating up milk for long enough to kill off any microbes. Heat doesn’t destroy minerals like calcium and pasteurization doesn’t deprive milk of its health benefits. If anything, raw milk is worse for you because it doesn’t have any vitamin D in it. We supplement our milk with vitamin D to avoid deficiency.
But the real danger to raw milk is its ability to transmit disease. In the early 20th century, the issue was tuberculosis — and the spread of bovine tuberculosis via contaminated milk was a major health concern. While tuberculosis is far rarer today, salmonella, E. coli, Listeria and other bacteria still make people sick. Pasteurization minimizes the chance of food outbreaks like this.
Whether H5N1 in milk could infect humans is unclear. However, early reports found that cats living on farms with infected cows got sick after drinking raw milk from the infected cattle.
But this is not something consumers need to worry about right now. Adequate testing of imported cattle and milk products, destroying milk from infected cows and standard infection-control measures should preserve the safety of the food supply. The final step, pasteurization, ensures milk is safe to drink and free of disease. So we can be fairly confident in saying the milk supply is safe. Just don’t drink raw milk.
Christopher Labos is a Montreal physician, co-host of the Body of Evidence podcast, and author of Does Coffee Cause Cancer?
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