All and all, 248 humans have died from the H5N1 according to WHO data as of January 2009. H5N1, as a strain, infects more species than any previously known flu virus, is deadlier than previous strains, and continues to evolve becoming both more widespread and more deadly. But even still, fears of a pandemic have yet to be realized. Now, researchers might have found the reason: our noses are too cold for the Avian flu. [...]
The difference in temperature, internally, between a human and a bird isn't all that different - people maintain an internal temperature of about 37 degrees celcius, whereas birds stay a little warmer, around 40 degrees celcius. Researchers from the University of North Carolina wanted to know how these temperature differences might affect avian influenza viruses. They took a avian virus strain, H4N6, and human flu H3N2, and tried to infect human airway epithelial cells - the cells that line our noses and lungs. Both, they found, could infect and replicate quite quickly human airway epthelial cells at 37 degrees celcius, though the avian ones were a little slower in general than the human ones. But when the temperature was dropped to that of our noses - a bit cooler 32 degrees celcius - the avian virus replication slowed to a snail's pace, 3-5 log units below the human virus' speed. They tried a different avian strain - H5N3 - and found the same results. So they tried the deadly virus itself, H5N1 isolated from a dead person, and even it fared poorly. It seems that something about avian flu viruses simply can't function right in cooler temperatures.
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