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Friday 07 May 2010
Flu virus transported by dust storms
Dust storms can increase levels in air, but experts question whether the virus remains infectious
Influenza viruses, including the avian H5N1 subtype, may be carried in the air for long distances and across continents by dust storms, according to new research in Taiwan. The concentration of influenza viruses in the air was found to be 20 to 30 times higher during dust storms than at other times.
The study is the first to measure influenza virus concentrations in ambient air, according to the authors. It follows a number of studies showing that airborne viruses can be found in indoor environments such as hospitals and offices.
Dust storms across Asia are becoming longer and more frequent as a result of desertification in China. Particles of dust stirred up by these storms can travel long distances, sometimes reaching as far as Europe or the USA. “The attachment of infectious viruses to dust particles moving across the ocean might enhance long-range host-to-host transport,” write the researchers, led by Pei-Shih Chen, of the Kaohsiung Medical University in Taiwan.
The finding might explain why not all outbreaks of bird flu in animals have been linked to movement of poultry or wild birds, the authors say. “H5N1 outbreaks in South Korea and Japan were not consistent with either reported poultry trade or the timing and direction of migratory bird travel during the month of outbreak, suggesting that other factors led to these introduction events,” they write. “Avian influenza outbreaks in downwind areas of Asian dust storms suggest that viruses might be transported by dust storms.”
To determine the concentration of airborne viruses the researchers directed samples of outdoor air onto Teflon filters in two air-monitoring stations in Taiwan, one rural and one urban. The amount of viral RNA present on the filters was then measured using quantitative PCR. They found that influenza A viruses, including H5N1 and other subtypes, were present in the air both during dust storms and on other days — but at significantly higher concentrations during dust storms. Avian influenza (H5N1) only made up a small number of the viruses detected, and were found only during dust storms.
However, the impact of this finding on human health is unclear, argue Don Beezhold and John Noti of the US Centers for Disease Control and Prevention, in an email sent to EHTF news. “The amount of detected virus during Asian dust storm days was only 21 or 31 times higher,” they say. “At best, this is only a modest increase in viral count.”
Beezhold and Noti agree that viruses could get carried by air over very long distances.
”But the real question is whether the virus remains active,” they write. “There are studies, including our own unpublished data, that indicate small amounts of aerosolized virus is infectious. The question is for how long and how far in the outdoor environment can viable virus travel?”
Influenza viruses can be inactivated by drying, ultraviolet radiation and atmospheric pollutants, explain Beezhold and Noti. All of these conditions would affect viruses in a dust storm. But the researchers also point to studies showing that by attaching to particles of dust, as might be expected during a dust storm, viruses can increase their chances of survival.
1. Chen P-S, Tsai FT, Lin CK, Yang C-Y, Chan C-C, Young C-Y, Lee C-H. Ambient Influenza and Avian Influenza Virus during Dust Storm Days and Background Days. Environmental Health Perspectives 2010. doi: 10.1289/ehp.0901782