Flu clues

CDC/ Dr. F. A. Murphy

The paper:
A. Lowen et al., “Influenza virus transmission is dependent on relative humidity and temperature,” PLoS Pathogens, 3(10): e151. (Cited 71 times)

The finding:
The reason why more people get the flu during colder months has long been a mystery. To investigate the role of weather conditions on flu transmission, researchers at the Mount Sinai School of Medicine in New York exposed guinea pigs to an H3N2 strand of the influenza virus. They then subjected the pigs to variations in temperature and humidity and found that aerosol transmission of influenza depends on low temperatures and low relative humidity, which they suggest help the virus travel through the nasal passage and linger in the air—thus explaining its winter peak.

The impact:
Trying to understand influenza’s distinct seasonality has been a real problem, says Eddie Holmes, an evolutionary biologist at Pennsylvania State University....

The model:
Mice have been the common model for influenza studies, yet they do not actually contract or transmit the virus. A breakthrough came in 2006, when Anice Lowen and her colleagues tested guinea pigs and found they were highly susceptible to the virus. (Proc Natl Acad Sci, 103:9988–92, 2006). “It’s rewarding to give something to the field that others can make use of,” Lowen says.

The future:
The researchers are currently repeating this same methodology with the H1N1 virus, trying to understand its rather unusual seasonality—a spring outbreak, low-level spread through the summer, and early epidemic in the fall.

Americans Sick with Flu, Avg U.S. Monthly Temp (°C):
August: 1.1% 22.58
December: 2.5% -1.01
Sources: Gallup Poll and National Climatic Data Center

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