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Why flu virus prefers to strike in winter

You probably have been affected by flu several times in your life, and it has certainly happened in cold winter months, at least if you don't live in tropical countries. Why is the flu virus more infectious when it's cold? A U.S. National Institutes of Health (NIH) has an explanation. When it's cold, the virus envelope, made of lipids, hardens to a gel which protects the virus itself. But when temperature goes higher, the gel melts and no longer protects the virus which loses its ability to spread from person to person. The researchers think this finding can open new ways to fight flu by focusing on the virus lipid membrane. But read more...
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Written by Roland Piquepaille, Inactive on

You probably have been affected by flu several times in your life, and it has certainly happened in cold winter months, at least if you don't live in tropical countries. Why is the flu virus more infectious when it's cold? A U.S. National Institutes of Health (NIH) has an explanation. When it's cold, the virus envelope, made of lipids, hardens to a gel which protects the virus itself. But when temperature goes higher, the gel melts and no longer protects the virus which loses its ability to spread from person to person. The researchers think this finding can open new ways to fight flu by focusing on the virus lipid membrane. But read more...

3D model of an influenza virus

You can see above a 3-D model of the influenza virus and its lipid envelope (Credit: this page on Wikipedia). You'll find many more details about the influenza virus on this other page.

This study has been led by Joshua Zimmerberg, chief of National Institute of Child Health and Human Development (NICHD)'s Laboratory of Cellular and Molecular Biophysics. Zimmerberg worked with colleagues from National Institute on Alcohol Abuse and Alcoholism (NIAAA)'s Laboratory of Membrane Biochemistry and Biophysics (LMBB) who developed a sophisticated magnetic resonance technique.

Here is what the NIH team has discovered. "Dr. Zimmerberg and his colleagues found that at temperatures slightly above freezing, the virus's lipid covering solidified into a gel. As temperatures approach 60 degrees Fahrenheit, the covering gradually thaws, eventually melting to a soupy mix. Cooler temperatures, apparently, cause the virus to form the rubbery outer covering that can withstand travel from person to person, Dr. Zimmerberg said. Once in the respiratory tract, the warm temperature in the body causes the covering to melt to its liquid form, so that the virus can infect the cells of its new host, he added. 'Like an M&M in your mouth, the protective covering melts when it enters the respiratory tract,' Dr. Zimmerberg said. 'It's only in this liquid phase that the virus is capable of entering a cell to infect it.'"

And here are some additional comments from NICHD Director Duane Alexander. "The study results open new avenues of research for thwarting winter flu outbreaks. Now that we understand how the flu virus protects itself so that it can spread from person to person, we can work on ways to interfere with that protective mechanism."

The scientific community doesn't completely agree with the results of this study. For example, here is a link to an article published by BBC Online News, "Why flu strikes in cold weather."

In this article, John Oxford, Professor of Virology at the Institute of Cell and Molecular Science (ICMS) of Queen Mary's School of Medicine in London, said the paper was interesting, but it might be premature to draw firm conclusions. Here are some of his comments. "If this is the case why do we get flu in tropical areas, where the temperature is 35C (95F) all the time? Places like Vietnam and Indonesia are predicted to the epicentre of a new outbreak of pandemic flu."

BBC Online News adds that "Professor Oxford said researchers had tried to link flu infection definitively to cold weather since the great Russian outbreak of 1890, but had failed to come up with conclusive proof of a link. 'I don't think this study provides anything like a definitive answer on the spread of the virus -- there must be some other factors that come into play,' he said."

For more information, this research work has been published by Nature Chemical Biology as an Advance Online Publication (AOP) on March 2, 2008 under the name "Progressive ordering with decreasing temperature of the phospholipids of influenza virus." Here is a link to the abstract.

So do you believe that NIH researchers are right or wrong? Drop me a note.

Sources: National Institutes of Health (NIH) news release, March 2, 2008; BBC Online News, March 4, 2008; and various websites

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