Cold truth.
Transmission rate of flu between guinea pigs increases when temperature and humidity are low but drops when they rise.
Credit: Anice Lowen/Mount Sinai School of Medicine
Posted on 10/23/2007 12:09:35 AM PDT by neverdem
With flu season almost upon us, it's a good time to ponder why influenza strikes us hardest in the winter months. A new study chalks it up to the fact that the virus appears to be more infectious at colder temperatures and lower humidity. The findings could lead to strategies that help curtail transmission of the disease.
Several explanations have been put forth to explain the seasonal rise in flu cases. Some infectious-disease specialists have blamed the rise on the fact that people tend to have more contact during the colder months because they spend more time indoors. Others speculate that people's immune systems may become weaker during the winter. But so far there has been no good evidence to support these claims. So a team led by virologist Peter Palese of Mount Sinai School of Medicine in New York City tested whether temperature and humidity played a role in the spread of flu.
In a series of experiments, the researchers housed four guinea pigs infected with a human flu virus in cages next to four healthy animals. By holding the temperature constant and adjusting the humidity, they found that the greatest transmission occurred at a low relative humidity of 20% to 35%, the conditions under which 75% to 100% of the uninfected guinea pigs contracted the virus. Only one of the animals became infected when the humidity reached 50%, and transmission was blocked when the humidity rose above 80%, the researchers report in the October issue of PloS Pathogens. For temperature, the greatest transmission occurred at 5°C, with all of the healthy animals becoming infected. No transmission occurred at 30°C.
"This offers a nice explanation for why we have more flu in the winter, because it gets transmitted better in the cold," Palese says. The findings need to be confirmed in people, he says, but a possible reason for the increased transmission is that the flu virus is more stable at colder temperatures and lower humidity. Our physical barriers for keeping out pathogens, such as the mucous membrane in the nose, may also be impaired under these conditions.
Raymond Tellier, a microbiologist at the Hospital for Sick Children in Toronto, Canada, says the findings indicate that raising the humidity in buildings, such as hospitals and nursing homes, could help prevent transmission of flu. Still, this strategy could be tricky, he notes, because higher humidity could encourage the growth of other pathogens, such as mold or the bacteria that cause Legionnaires' disease. "You don't want to reduce one infectious disease only to increase another," Tellier says.
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This means global warming is a flu blocker. Two catastrophe theories are about to collide head on.
FOUR? Four test animals is not a large enough sample size to mean anything. Couldn’t they afford a few dozen critters? Not good science.
I put a lot of blame on holiday gatherings and children.
That's still a very small sample size, but valid for a first investigational study, i.e., enough to justify further research.
Flu germs travel through dry air easier than humid air because dry air is less dense than humid air.
I figured this all out without the use of lab animals. When do I get my PhD and grant money?
(Note: No guinea pigs were injured in the creation of this post.)
It’s a start, but each sample of 4 g-pigs would contain ones with different resistance to the flu. If one sample had one with high resistance, he alone would skew the results by 25%. And if another group had one with a low resistance, the same would happen in the other direction. In other words, maybe the conditions have nothing to do with it but the varying resistances of the individual pigs do.
A larger sample of dozens would be less skewed by individual pigs picked by chance with high or low resistance.
If I picked 4 kids at random and tried to sell them drugs, maybe 1 will buy. Then on Sunday, I pick 4 more kids at random and 2 buy. Headlines say, “Kids more likely to buy drugs on Sundays!”
Results
"Twenty replicate experiments were performed in which all factors remained constant except for the RH and/or temperature inside the environmental chamber. Each experiment involved eight guinea pigs, and transmission under each set of conditions was assessed in duplicate."
--snip--
Analysis of expression levels of mediators of innate immunity.
"Guinea pigs were inoculated with 103 PFU of Pan/99 virus intranasally and immediately housed under the appropriate conditions (5 °C or 20 °C and 35% RH). At days 1, 2, 3, 5, and 7 post-infection, three guinea pigs were killed and their nasal turbinates removed."
Read the study linked at the end of the article.
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