Navigation Links
NIH grantees rebut theory that seasonal flu strains originate in tropical regions
Date:11/16/2011

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 Surveillance and 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.

To test this theory, researchers led by Justin Bahl, Ph.D., and Gavin J.D. Smith, Ph.D., of the Duke-National University Graduate Medical School in Singapore, genetically analyzed strains of H3N2 influenza virus, a common cause of seasonal influenza among humans, collected between 2003 and 2006. They sequenced the full genome of 105 flu virus samples from Hong Kong and compared these with H3N2 virus sequences obtained from seven geographic areas with varying climates, including five temperate regions (Australia, Europe, Japan, the United States, and New Zealand) and two tropical regions (Hong Kong and Southeast Asia). The strains were arranged into a phylogenetic, or family, tree, showing the relationships between the strains and how they evolved over time.

"Earlier genetic studies had looked at H3N2 in a global context and concluded that new strains came from the tropics," said Dr. Bahl. "However, in those studies, a lot of key genetic data from the tropics was missing." This made it difficult to draw a firm conclusion about the origin of new flu strains, he said.

The researchers found that in temperate regions where flu seasons are relatively short, many new H3N2 virus strains arise every year, but they rarely persist from one season to the next. However, in Hong Kong and Southeast Asia, where flu seasons occur for longer periods of time, strains do persist between seasons.

Keeping these patterns in mind, the investigators traced the geographical movement of the strains to determine whether new flu strains actually originate in tropical regions. Instead, they found that influenza strains frequently migrate back and forth between tropical and temperate regions, and that the tropical regions were not necessarily the source of new strains.

In fact, 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.


'/>"/>

Contact: Nalini Padmanabhan
padmanabhannm@niaid.nih.gov
301-402-1663
NIH/National Institute of Allergy and Infectious Diseases
Source:Eurekalert

Related medicine news :

1. AACR recognizes its newest grantees at 102nd Annual Meeting 2011
2. Malaria-transmitting mosquito evolving, NIH grantees find
3. New findings contradict dominant theory in Alzheimers disease
4. UofL School of Nursing researcher plans to build on successful aging theory
5. New Memory Theory Focuses on Brain-Wave Levels
6. Controversial TOFT theory of cancer versus SMT model: Authors do battle in BioEssays
7. Can chaos theory help predict heart attacks?
8. Study Challenges Key Autism Theory
9. Evidence-based medicine theory can be applied to frequent flying says US professor
10. Theory of single stem cell for blood components challenged
11. MRSA infection shown to be seasonal
Post Your Comments:
*Name:
*Comment:
*Email:
(Date:6/26/2017)... ... 2017 , ... Maryland’s soybean farmers have improved the sustainability ... the United Soybean Board. , Thanks to the responsible use of technology ... on less land per bushel, the report says. The United Soybean Board’s “Soy ...
(Date:6/26/2017)... ... June 26, 2017 , ... New patients with missing ... Cotey, with or without a referral. Dr. Cotey is a trusted dentist who has ... tooth replacement option. , Patients with missing teeth in Fitchburg, WI, are encouraged to ...
(Date:6/25/2017)... ... ... CareSet Labs released the Root NPI Graph today at the 2017 Academy ... of the Doctor Referral teaming dataset commonly available from Medicare. , Originally created through ... “Doctor Referral Dataset” as released by Medicare and “DocGraph” as released by Trotter, the ...
(Date:6/24/2017)... ... June 24, 2017 , ... Dr. Mitchell Mehlman ... Road in Lake Ronkonkoma, Dental365 offers patients high-quality and affordable routine and emergency ... the dentist fit into their patients’ busy lifestyles. Dental365 also gladly work with ...
(Date:6/23/2017)... ... ... By scoring 100% for fiscal management and accountability, the Arthritis National Research ... Charity Navigator, validating ANRF's work as a top charity in America. , This achievement ... earns ANRF a spot on their “ 10 Charities Worth Watching ” list as ...
Breaking Medicine News(10 mins):
(Date:6/8/2017)... , June 8, 2017   Responding to Heath ... and the death of singer Chris Cornell in ... Rights International offers a free online psychiatric ... consumers and families about psychotropic drug risks. ... who died from an accidental overdose, has called for tighter ...
(Date:6/7/2017)... Iowa , June 6, 2017  Diplomat Specialty Infusion Group, ... sterile compounding environment to its Iowa location. ... Urbandale now features an ISO 7 cleanroom—the standard ... controlled environment with a low level of pollutants. ... more IV nutrition consumers and better serve our Iowa ...
(Date:6/2/2017)... June 2, 2017  NxStage Medical, Inc. (Nasdaq:  NXTM), a leading ... announced new findings demonstrating positive biochemical outcomes related to ... One™. The data will be presented at the ERA-EDTA ... Madrid, Spain . The research ... Dialysis Network in Europe ...
Breaking Medicine Technology: