Ambient Influenza and Avian Influenza Virus during Dust Storm Days and Background Days

Article excerpt

BACKGROUND: The spread of influenza and highly pathogenic avian influenza (H5N1) presents a significant threat to human health. Avian influenza outbreaks in downwind areas of Asian dust storms (ADS) suggest that viruses might be transported by dust storms.

OBJECTIVES: We developed a technique to measure ambient influenza and avian influenza viruses. We then used this technique to measure concentrations of these viruses on ADS days and background days, and to assess the relationships between ambient influenza and avian influenza viruses, and air pollutants.

METHODS: A high-volume air sampler was used in parallel with a filter cassette to evaluate spiked samples and unspiked samples. Then, air samples were monitored during ADS seasons using a filter cassette coupled with a real-time quantitative polymerase chain reaction (qPCR) assay. Air samples were monitored during ADS season (1 January to 31 May 2006).

RESULTS: We successfully quantified ambient influenza virus using the filtration/real-time qPCR method during ADS days and background days. To our knowledge, this is the first report describing the concentration of influenza virus in ambient air. In both the spiked and unspiked samples, the concentration of influenza virus sampled using the filter cassette was higher than that using the high-volume sampler. The concentration of ambient influenza A virus was significantly higher during the ADS days than during the background days.

CONCLUSIONS: Our data imply the possibility of long-range transport of influenza virus.

KEY WORDS: ambient virus, avian influenza virus, bioaerosol, dust storm, infectious bioaerosol, influenza virus, quantification, real-time qPCR. Environ Health Perspect 118:1211-1216 (2010). doi: 10.1289/ehp.0901782 [Online 30 April 2010]

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The spread of highly pathogenic avian influenza (H5N1) into Asia, Europe, and even Africa has strongly affected the poultry industry and presents a significant threat to human health. To date, 363 human cases of avian influenza (61% of them fatal) have been officially reported by the World Health Organization (2008). In 2003, the rapid spread of severe acute respiratory syndrome (SARS) to Asia, North America, Europe, and Australia during the first two quarters of the year illustrated the speed at which influenza and avian influenza pandemics can spread across the world. Influenza and avian influenza outbreaks are expected to be much harder to control than SARS because, in contrast with SARS, people infected with influenza are contagious before the onset of case-defining symptoms (Koh et al. 2008). Therefore, it is important to understand possible transmission pathways between countries in preparation for influenza or avian influenza pandemics.

How the highly pathogenic H5N1 avian influenza has spread between countries has been extensively debated. In a previous study, Kilpatrick et al. (2006) integrated data on phylogenic relationships of virus isolates, poultry and wild bird trade, and migratory bird movements to determine the pathway for the introduction of H5N1 into each of 52 countries. Their results demonstrated that 9 of 21 H5N1 inductions into countries in Asia were most likely through poultry, and 3 of 21 were through migrating birds. However, 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.

Avian influenza outbreaks in Japan and South Korea, which, like Taiwan, include areas that are downwind of Asian dust storms (ADS), occurred during the ADS season, according to reports from the World Organization for Animal Health (OIE 2006). With increasing evidence from epidemiological studies, increased health effects, including respiratory diseases, during ADS days in downwind areas have recently drawn much attention (Bell et al. …