NIH grantees rebut theory that seasonal flu strains originate in tropical regions

 

Viral Cell Invasion and Replication

From the 16 November 2011 Eureka News Alert article

NIH grantees rebut theory that seasonal flu strains originate in tropical regions

Influenza researchers have found that flu strains migrate back and forth between different regions of the world, evolving along the way. This is contrary to the common belief that flu strains from the tropics are the source of global seasonal epidemics.

The research appeared online on Nov. 14 in the Proceedings of the National Academy of Sciences. It was supported in part by the Centers of Excellence for Influenza Research and Surveillanceand the Influenza Genome Sequencing Project, funded by the National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health.

“This study helps us to better understand why the persistence, movement and evolution of flu viruses are complex and largely unpredictable,” said NIAID Director Anthony S. Fauci, M.D. “These findings also remind us of the importance of maintaining vigilance in our global influenza surveillance efforts.”

Previous studies had shown that in general, influenza viruses in tropical regions tend to be more varied and circulate year-round rather than seasonally, like flu viruses found in temperate regions with more moderate climates. The prevailing theory had been that tropical areas of the world may be the source of flu viruses from which new seasonal flu strains originate….

…

none of the seven temperate and tropical regions they examined was the source of all new H3N2 flu strains in a given year. The migration pattern was more complex. Virus strains moved from one region to several others each year, and flu outbreaks were traced back to more than one source. And although the virus that migrated between Southeast Asia and Hong Kong persisted over time, its persistence was caused by the introduction of virus from the temperate regions. Therefore, the tropical regions did not maintain a source for the annual H3N2 influenza epidemics. Further, in contrast to annual flu epidemics in temperate climates, relatively low levels of genetic diversity among flu strains and no seasonal fluctuations were found in the tropical regions.

“We found that the H3N2 influenza virus population is constantly moving between regions, and every region is a potential source for new epidemics,” said Dr. Bahl. “Regions with more connections to others, such as travel centers, may contribute more to the global diversity of circulating viruses.”

The complexity of the global virus circulation found in the study suggests that efforts to control flu should include region-specific strategies, according to the researchers. In future studies, the researchers intend to examine whether the virus behaves differently in temperate and tropical areas, including regions not included in this analysis, and in places that are more or less connected to the rest of the world.

 

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The new findings build on earlier influenza virus evolution research funded in part by NIAID (http://www.niaid.nih.gov/news/newsreleases/2008/Pages/flu_evolution.aspx). For more information about NIAID’s influenza research, visit (http://www.niaid.nih.gov/topics/Flu/Pages/default.aspx).

Read the article

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