| NEW YORK
NEW YORK (Reuters Health) - Influenza viruses that normally infect birds are adapted to proliferate most efficiently at temperatures higher than those encountered in the upper airways of humans, according to a new report.
"I think this study helps explain two things," Dr. Raymond J. Pickles told Reuters Health. It could be the reason why people need to be exposed to large amounts of bird virus to get infected "and, second, why these infected individuals do not show the classic cough, sneezing, and transmissibility of seasonal flu's."
Pickles, at the University of North Carolina at Chapel Hill, and his colleagues developed a model of the human airway to investigate the influence of temperature on human and bird influenza virus replication and spread.
Human influenza virus replicated to a similar degree at the temperature found deep in the lungs (37C) and at the temperature found up closer to the nose (32C). The growth of bird viruses, on the other hand, slowed down by several orders of magnitude at the lower temperature, the researchers report in the medical journal PLoS Pathogens.
The cell damage caused by bird flu virus was also significantly delayed at the lower temperature compared with the higher temperature.
"The real implication from this research is that, given that the most usual inoculation route for influenza virus would be the nose, mouth, and eyes, these avian viruses would have a harder time than transmittable human viruses in setting up an infection due to the lower temperatures of these regions," Pickles explained. "This gives the host immune response additional time to respond and limit infection."
SOURCE: PLoS Pathogens, May 15, 2009.