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As swine flu spreads around the globe, scientists are seeking to build their understanding of the virus — particularly the likelihood that it will mutate. From the wealth of information in the media, SciDev.Net has selected some of the best articles considering the science behind swine flu.

According to Wendy Barclay — professor of influenza virology at the UK-based Imperial College London — swine flu, now known as A(H1N1), is a 'triple reassortment' virus. It is made up of segments from human, swine and avian viruses, Barclay told New Scientist in an expert analysis.

Speaking to Science for an article on swine flu mutation, Kennedy Shortridge — a virologist at the University of Hong Kong — warned that as the virus spreads further this mixture is likely to increase: "… the farther the virus spreads, the more chance it will mix, or reassort, with other flu viruses in circulation and turn into something more lethal".

He said that there are human strains of the virus in areas that are resistant to the current treatment Tamiflu and urged the sequencing of as many viral samples as possible to help predict changes in the virus.

In an attempt to predict the virus's spread, Ira Longini and colleagues at the US-based University of Washington are trying to acquire as much data as possible on the virus's basic reproductive number, R0, a variable that reveals the number of new infections caused by each infected person. Longini told Science in the same article that this is the key factor in determining the virus's spread.

Scientists are also eager to find out "whether a virus must mutate to move from pigs to humans and whether, as is the case with bird flu in humans, a specific mutation makes it more virulent," Science reports.

A strategy to postpone the emergence of resistance is to "hold off using your primary drug until the cumulative number of cases reaches a sufficiently high number," says Joseph Wu of the University of Hong Kong. He told New Scientist that stockpiling just one drug would encourage resistance.

One mystery is the virus's origins.

UK newspaper The Guardian reports that UN scientists are trying to determine whether La Gloria, Mexico, is the virus's source. The village is suspected because samples acquired from a five-year-old there provide the earliest confirmed case of the disease. Other theories include migrant workers bringing the virus to Mexico from California, or that the earliest source is a 39-year-old woman in the southern Mexican state of Oaxaca.

Scientists are also investigating why sufferers outside Mexico have experienced comparatively mild symptoms, Barclay told New Scientist. As yet there is no evidence that the genetic makeup of the Mexican strains differ from those in the United States, for example, says Barclay.

BBC Online reports that preliminary analysis of the virus suggests that it is "a fairly mild strain". In a summary of what is known about swine flu, scientists say further mutation is required to cause mass deaths, but future evolution of the virus remains unknown. UK scientists will begin work today (1 May) on samples of the virus sent from the US. The research is essential in order to work out the structure of the virus, its origins and its propensity to spread.

Barclay told BBC Online that "initial indications suggest there is nothing about the genetic makeup of the new virus which is a cause for particular concern".

Preliminary "guesswork" has found that H1N1 attaches itself to the upper respiratory tract, spreading easily via coughing and sneezing but causing only mild infection. This is unlike the H5N1 avian influenza virus, which binds further down in the lungs and causes more severe illness, even though human transmission is rare.

But it will take "weeks and months of biological analysis" to fully determine H1N1's potential, reports BBC Online.


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