These findings suggest that by focusing surveillance efforts on East and Southeast Asia, researchers may be able to extend their forecast of the flu strains most likely to cause epidemics, which may in turn help experts decide which strains should go in the flu vaccine each year.
The study, by a team of researchers from Europe, Australia, Japan and the United States, appears in the 18 April issue of the journal Science, which is published by AAAS, the nonprofit science society.
“The flu virus is constantly mutating, so it’s a major challenge for public health as well as a fascinating example of evolution in action. This study advances our knowledge of how new flu strains spread across the globe and how epidemics arise,” said Katrina Kelner, Science’s deputy managing editor, life sciences.
Colin Russell of the University of Cambridge in the United Kingdom and his colleagues analyzed 13,000 samples of influenza A (H3N2) virus, collected across six continents from 2002 to 2007 by the World Health Organization Global Influenza Surveillance Network. This subtype of influenza is currently the major cause of flu-related illness and death in humans.
The researchers compared physical differences in a surface protein, called hemagglutinin, across the different samples. Hemagglutinin is the primary target of the immune response, and even small changes can allow the virus to evade the immune system and cause disease.
In a subset of the samples, the researchers also compared the sequences of the gene that codes for hemagglutinin.
Together, these analyses allowed the researchers to identify different strains of A (H3N2) as they arrived at new locations around the world over the five-year period. The results revealed that strains emerge in East and Southeast Asia and then about six to nine months later reach Europe and North America. Several months later still, the strains arrive in South America. Essentially, once the strains leave East and Southeast Asia they enter an evolutionary graveyard.
“The ultimate goal of our collaboration is to increase our ability to predict the evolution of influenza viruses. This study is one step along that path and in particular highlights the importance of ongoing collaborations and surveillance in East and Southeast Asia, and of expanding these collaborations in the future,” said Derek Smith of the University of Cambridge, who is the corresponding author of the study.
Annual influenza epidemics are thought to result in 3 to 5 million cases of severe illness, and between 250,000 and 500,000 deaths every year, according to the World Health Organization (http://www.who.int/mediacentre/factsheets/fs211/en/index.html).
A (H3N2) is a subtype of the influenza A virus, and it is one of the three flu viruses included – in dead or in a weakened state – in the flu vaccine. The others are the influenza A (H1N1) subtype and the influenza B virus. Each year, the World Health Organization decides which strains within these three categories to include in the next vaccine, based on the recent activity of strains that are currently circulation.
The authors emphasized that the flu vaccine currently works extremely well, protecting about 300 million people from the disease each year, and that people should continue to be vaccinated annually. But, from time to time, a new strain begins infecting people after the vaccine has already been produced.
For decades, researchers haven’t known how influenza viruses migrate around the world. According to some of the scenarios that have been proposed, the viruses may migrate between the Northern and Southern hemispheres following the seasons, or they may have come out of the tropics where they were thought to circulate continuously, or they may have come out of China.
The Science study shows instead that each year since 2002, influenza A (H3N2) viruses have migrated out of what the authors call the “East and Southeast Asian circulation network,” and from there spread around the world.
Why Asia" For reasons that aren’t well-understood, flu epidemics break out during the rainy seasons in the tropics of East and Southeast Asia. On continents at higher latitudes, on the other hand, flu season simply occurs for a few months during the wintertime. Within Asia, different regions experience the rainy season at different times of year.
“Flu epidemics appear to be driven by seasonal factors such as winter, or rainy seasons. So there can be cities that are only 700 miles away from each other, such as Bangkok and Kuala Lumpur, which have epidemics six months apart. There is a lot of variability like this in East and Southeast Asia, so lots of opportunity for an epidemic in one country to seed an epidemic to another nearby country, like a baton passed by runners in a relay race,” Smith said.
“Our study is an example of the tremendous synergy between influenza science and public health,” he said. “The World Health Organization’s Global Influenza Surveillance Network tracks the evolution of influenza viruses for the primary purpose of influenza vaccine strain selection, but this also enables basic work on evolution.”
"The Global Circulation of Seasonal Influenza A (H3N2) Viruses," by C.A. Russell; T.C. Jones; A, Mosterin; E. Skepner; D.J. Smith at University of Cambridge in Cambridge, UK; T.C. Jones; J.C. de Jong; A.D.M.E. Osterhaus; G.F. Rimmelzwaan; R.A.M. Fouchier; D.J. Smith at Erasmus Medical Centre in Rotterdam, Netherlands; T.C. Jones; A. Mosterin at Universitat Pompeu Fabra in Barcelona, Spain; I.G. Barr; N.J. Cox; R.J. Garten; V. Gregory; I.D. Gust; A.W. Hampson; A.J. Hay; A.C. Hurt; A. Kelso; A.I. Klimov; T. Kageyama; N. Komadina; Y.P. Lin; M. Obuchi; T. Odagiri; M.W. Shaw; M. Tashiro at World Health Organization (WHO) Collaborating Centre for Reference and Research on Influenza in Melbourne, VIC, Australia; N.J. Cox; R.J. Garten; A.I. Kilmov; M.W. Shaw at Centers for Disease Control and Prevention in Atlanta, GA; V. Gregory; A.J. Hay; Y.P. Lin at National Institute for Medical Research in London, UK; T. Kageyama; M. Obuchi; T. Odagiri; M. Tashiro at National Institute for Infectious Diseases in Tokyo, Japan; A.S. Lapedes at Los Alamos National Laboratory in Los Alamos, NM; K. Stohr at Novartis Vaccines and Diagnostics in Boston, MA.
This study was funded by the National Institutes of Health Director’s Pioneer Award (http://nihroadmap.nih.gov/pioneer), the National Institute of Allergy and Infectious Diseases, the NWO Netherlands Influenza Vaccine Research Centre, the Australian Government Department of Health and Aging, and the Medical Research Council.
The American Association for the Advancement of Science (AAAS) is the world's largest general scientific society, and publisher of the journal Science (www.sciencemag.org). AAAS was founded in 1848, and serves 262 affiliated societies and academies of science, reaching 10 million individuals. Science has the largest paid circulation of any peer-reviewed general science journal in the world, with an estimated total readership of 1 million. The nonprofit AAAS (www.aaas.org) is open to all and fulfills its mission to "advance science and serve society" through initiatives in science policy; international programs; science education; and more. For the latest research news, log onto EurekAlert!, www.eurekalert.org, the premier science-news Web site, a service of AAAS.
Natasha Pinol | EurekAlert!
Collagen nanofibrils in mammalian tissues get stronger with exercise
14.12.2018 | University of Illinois College of Engineering
New discoveries predict ability to forecast dementia from single molecule
12.12.2018 | UT Southwestern Medical Center
The more objects we make "smart," from watches to entire buildings, the greater the need for these devices to store and retrieve massive amounts of data quickly without consuming too much power.
Millions of new memory cells could be part of a computer chip and provide that speed and energy savings, thanks to the discovery of a previously unobserved...
What if, instead of turning up the thermostat, you could warm up with high-tech, flexible patches sewn into your clothes - while significantly reducing your...
A widely used diabetes medication combined with an antihypertensive drug specifically inhibits tumor growth – this was discovered by researchers from the University of Basel’s Biozentrum two years ago. In a follow-up study, recently published in “Cell Reports”, the scientists report that this drug cocktail induces cancer cell death by switching off their energy supply.
The widely used anti-diabetes drug metformin not only reduces blood sugar but also has an anti-cancer effect. However, the metformin dose commonly used in the...
A research team from the University of Zurich has developed a new drone that can retract its propeller arms in flight and make itself small to fit through narrow gaps and holes. This is particularly useful when searching for victims of natural disasters.
Inspecting a damaged building after an earthquake or during a fire is exactly the kind of job that human rescuers would like drones to do for them. A flying...
Over the last decade, there has been much excitement about the discovery, recognised by the Nobel Prize in Physics only two years ago, that there are two types...
12.12.2018 | Event News
10.12.2018 | Event News
06.12.2018 | Event News
14.12.2018 | Power and Electrical Engineering
14.12.2018 | Physics and Astronomy
14.12.2018 | Physics and Astronomy