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Airline, ground transportation routes influence spread of influenza
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Recent data suggest airline and road travel routes may influence the distribution of the flu virus in the United States.
Researchers examined the impact of air and commuter travel networks on the intraseasonal genetic structure of influenza A epidemics in the U.S. Spatially referenced hemagglutinin nucleotide sequences from 2003 to 2013 were collected to evaluate intraseasonal pairwise genetic distances in relation to geographic and network measures of distance.
The analysis of travel networks revealed there are roughly 1.6 million interstate airline travelers daily during influenza season, with most states well-connected to other states via air travel. In addition, more than 3.8 million individuals traveled daily across interstate roadways. However, this travel primarily occurs between neighboring states, and is more prevalent in the East.
In analyzing spatial and genetic distance metrics, the researchers found that while all three distance measures (geographic distance, interstate airline connections and interstate commuter connections) were associated with genetic distance, there was a greater link between the commuter network vs. any other measure of spatial or network distance for the H1N1 influenza subtype. Moreover, after accounting for geographic distance, the association between genetic distance and the commuter network remained significant. According to the researchers, these findings suggested that the relative degree of movement over space has a greater impact on the route of pathogen transmission than the geographic closeness of the sampling sites.
Figure 1. This photo of the U.S. Interstate commuter network shows the number of people traveling daily between states for work.
Source:Courtesy of Bozick, CC-BY
Most of the data evaluated for H3N2 subtype did not reveal a population structure, although geographic and commuter distance were associated with genetic distance.
According to the researchers, these results suggested that when population structure is identifiable, regional commuter networks appear to have the most significant effect.
“Our results highlight the importance of utilizing host movement data in characterizing the underlying genetic structure of pathogen populations and demonstrate a need for a greater understanding of the differential effects of host movement networks on pathogen transmission at various spatial scales,” the researchers wrote. – by Jen Byrne
Disclosure: The researchers report no relevant financial disclosures.
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