Bangalore: The term “Asian contagion” may have a sinister ring to it given recent developments in global financial markets, but according to new research, there is a literal meaning to it.
The seasonal influenza virus that infects millions of people around the world every year emerges and evolves in overlapping epidemics in Asia and then heads out to the rest of the world.
Reporting the migration of the virus in Friday’s issue of Science, an international team of researchers says that the strains emerge in East and South-East (E&SE) Asia and then, about six to nine months later, reach Europe and North America, before they finally die out in South America.
The findings, the researchers add, suggest that by better surveillance in these Asian regions, researchers could forecast the flu strains that are most likely to cause epidemics in most parts of the world and, consequently, decide which strains should be included in the vaccine each year.
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Influenza A (H3N2) is currently the major cause of sickness and death from human influenza worldwide. The World Health Organization estimates that annual influenza epidemics cause three-five million severe illnesses and between 250,000 and 500,000 deaths every year.
Globally, the flu vaccine works well and protects about 300 million people from the disease, but India does not have a planned or mandatory vaccination programme for flu. This could, however, change as WHO has recommended the use of seasonal flu vaccine, particularly by high-risk groups, as a protection against the highly pathogenic H5N1 avian influenza virus which is circulating in India and other Asian regions.
In fact, the Influenza Foundation of India, an advisory body for creating awareness on the disease, earlier this year issued recommendations to prevent seasonal flu, especially during an outbreak of the bird flu.
In the present study, Colin Russell of the University of Cambridge in the UK and his colleagues analysed 13,000 samples of H3N2 virus collected from six continents between 2002 and 2007 by the WHO Global Influenza Surveillance Network.
The researchers compared physical differences in a surface protein called hemagglutinin across all samples. This protein is the primary target of the immune response and even a tiny change can allow the virus to evade the immune system and cause the disease. In a small set of these samples, researchers also compared the sequences of the gene that codes for hemagglutinin.
The result: Researchers were able to identify different strains of H3N2 as they travelled to new locations around the world over these five years. “Essentially, once the strains leave E&SE Asia, they enter an evolutionary graveyard.”
H3N2 virus first appeared in humans in 1968 and is one of the subtypes in the three flu viruses included in the flu vaccine, the other two being H1N1 and the influenza B virus.
Besides throwing light on the seasonal flu viruses, “it’s possible that these findings can be applied to study evolution of other influenza viruses, including the avian flu,” says a virologist at the National Institute of Virology (NIV) in Pune, who did not want to be named because scientists at the institute need prior permission to talk to the media.
However, the ultimate goal of this research collaboration, says Derek Smith of the University of Cambridge and a co-author of the paper, is to “increase our ability to predict the evolution of influenza viruses,” which will lead to improvements in flu vaccine design.
Due to tropical climate and a rainy season that is spread over several months, flu epidemics occur in the E&SE Asian regions a few months apart. This presents an opportunity for an epidemic in one country to start one in another nearby country, “like a baton passed by runners in a relay race,” says Smith.
But India’s role in this flu virus “circulation” is not yet fully known. With about 17% of the world’s population and varied regional climates, it may be sufficiently heterogeneous to maintain its own network of overlapping epidemics, says Russell. “India’s strong connections with E&SE Asia and a high level of internal connectivity also mean that it is at least likely to be seeded from the E&SE Asian circulation network and might seed back forming an extended E&SE Asian-Indian circulation network,” he adds.
It is not impossible that India might sustain its own independent network though no evidence for this was found from the Indian data in the study, says Smith. His group is, however, collaborating with NIV and the Indian Council of Medical Research to investigate influenza virus epidemiology and evolution in India.