URL: http://www.msnbc.msn.com/id/23435961/

Study shows why winter is 'flu season'

Coating protects viruses against cold -- so they can infect you more
easily
Reuters
updated
12:38 p.m. CT, Sun.,
March. 2, 2008

WASHINGTON - Influenza viruses coat themselves in fatty material that
hardens and protects them in colder temperatures -- a finding that
could explain why winter is the flu season, U.S. researchers reported
on Sunday.

This butter-like coating melts in the respiratory tract, allowing the
virus to infect cells, the team at the National Institutes of Health
found.

"Like an M&M in your mouth, the protective covering melts when it
enters the respiratory tract," said Joshua Zimmerberg of the National
Institute of Child Health and Human Development (NICHD), who led the
study.

The NICHD is one of the National Institutes of Health.

"It's only in this liquid phase that the virus is capable of entering
a cell to infect it."

Experts have long pondered why flu and other respiratory viruses
spread more in winter. No one explanation, such as people staying
indoors more, or the destructive effect of the sun's radiation in
summer, has fully explained it.

The new report, published in the journal Nature Chemical Biology,
could lead to new ways to prevent and treat flu, said NICHD Director
Duane Alexander.

"The study results open new avenues of research for thwarting winter
flu outbreaks," Alexander said in a statement.

"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."

Zimmerman's team used a type of imaging called nuclear magnetic
resonance imaging to look at the outer coat of flu viruses.

Going out into the world
Viruses cannot replicate on their own but instead must hijack a living
cell. Influenza viruses have a membrane-like outer coating that they
fuse to the victim cell.

They inject genetic material into the cell, turning it into a virus
factory. Some types of viruses simply explode out of these hijacked
cells, but influenza instead "buds" out, and uses lipids such as
cholesterol from the cells to make a membrane to help it do so.

"This is the protein we make vaccines against," Zimmerman said in a
telephone interview. The outside envelope protein, called
hemagglutinin, gives influenza viruses the "H" in their names.

Inside a nice, warm cell, the hemagglutinin is liquid. But at cooler
temperatures it starts a process that resembles crystallization,
called ordering.

"It solidifies gradually all the way down from 40 degrees Celsius (104
degrees F) down to 4 degrees C (39 degrees F)," Zimmerman said.

"I believe that this gradualness lets it exist at every temperature."

In warmer outdoor temperatures this protective coating melts, and
unless it is inside a living person or animal, the virus perishes.

A cure for flu?
The finding could also help scientists find new ways to eradicate
influenza. In cold temperatures, the hard lipid shell might withstand
certain detergents, making it more difficult to wash the virus off of
hands and surfaces.

Influenza and other respiratory viruses are spread in small droplets
broadcast by coughing, sneezing and talking and which can also settle
onto surfaces, to be picked up on fingertips.

Copyright 2008 Reuters.

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