Tropical reservoir for human influenza?

Each winter, influenza makes many people in the U.S. and other countries very sick. The virus even kills some of those unfortunate enough to be infected. You can get the 'flu even if you have had it previously, because your immune system can fail to recognize the virus as something it has already encountered. This is because the viral proteins (antigens) that trigger an antibody response can change considerably from year to year.

Although it is well known that influenza changes antigenically from one winter to the next, relatively little is known about how the whole genome of the influenza A virus evolves and how different strains spread geographically.

Eddie Holmes and Martha Nelson from the Center for Infectious Disease Dynamics, together with collaborators in Edinburgh (UK), Oxford (UK) and the National Institutes of Health, have now characterized the evolutionary dynamics of two major human influenza subtypes, A/H1N1 and A/H3N2. Their findings are published in the journal Nature.

The researchers examined more than 1300 whole influenza genomes collected in the U.S. and New Zealand, to characterize how genetic diversity in these two viral lineages has changed over the course of 12 years beginning in the early 1990s.

The observed spatio-temporal changes in viral diversity suggest that new influenza strains arise from a reservoir in the tropics, possibly in southeastern Asia, and move out to temperate regions. This conclusion has implications for recommendations on where and when to focus surveillance for human influenza strains that should be countered using vaccines.

• Read a longer synopsis of the researchers' findings, on the Center for Infectious Disease Dynamics website
• Read a press release about this research, on the Penn State Live website
• Read the full paper on the Nature website