U.S. Department of Health and Human Services
NATIONAL INSTITUTES OF HEALTH NIH News
National Institute of Child Health and Human Development (NICHD)
<http://www.nichd.nih.gov>
For Immediate Release: Sunday, March 2, 2008
Contact: Robert Bock or Marianne Glass Miller, 301-496-5133, <e-mail:
[email protected]>
NIH SCIENTISTS FIND WHY FLU VIRUS SPREADS IN COLD WEATHER
A finding by a team of scientists at the National Institutes of Health
may account for why the flu virus is more infectious in cold winter
temperatures than during the warmer months.
Briefly, at winter temperatures, the virus's outer covering, or
envelope, hardens to a rubbery gel that shields the virus as it passes from
person to person. With warmer weather, however, the protective gel melts
to a liquid phase. But this liquid phase, apparently, isn't tough
enough to protect the virus against the elements, and so the virus loses its
ability to spread from person to person.
The findings were published on line March 2 in Nature Chemical Biology.
The study was a collaboration between researchers at two NIH
institutes, the National Institute of Child Health and Human Development, and
the National Institute of Alcohol Abuse and Alcoholism.
"The study results open new avenues of research for thwarting winter
flu outbreaks," said NICHD Director Duane Alexander. "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."
Flu is caused by a group of viruses known as Influenza viruses. These
are usually spread from person to person through coughs and sneezes.
Infection with flu virus can cause fever, sore throat, muscle aches,
severe headache, coughing, weakness and general discomfort. The virus can
cause mild to severe illness, and at times can lead to death.
In October of 2007, researchers working with guinea pigs showed that
animals sick with the flu were more likely to get other guinea pigs sick
at colder temperatures than at warmer temperatures.
In the current study, the NIH researchers used a technique called magic
angle spinning nuclear magnetic resonance to create detailed images of
how the virus's outer membrane responded to variations in temperature.
The virus's outer membrane is composed chiefly of molecules known as
lipids, explained the study's senior author Joshua Zimmerberg, Ph.D.,
Chief of NICHD's Laboratory Of Cellular And Molecular Biophysics. This
family of molecules does not mix with water, and includes oils, fats,
waxes, and cholesterol.
Dr. Zimmerberg and his colleagues found that at temperatures slightly
above freezing, the virus's lipid covering solidified into a gel. When
temperatures reached about 60 degrees Fahrenheit, the covering began to
thaw, and the covering turned to a soupy mix.
Cooler temperatures, apparently, cause the virus to form the rubbery
outer covering that can withstand travel from person to person. 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.
"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.
In spring and summer, however, the temperatures are too high to allow
the viral membrane to enter its gel state. The individual flu viruses
apparently dry out and weaken, and the flu
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