Avian flu becoming more resistant to antiviral drugs, says University of Colo...( A new University of Colorado at Boul...)

A new University of Colorado at Boulder study shows the resistance of the avian flu virus to a major class of antiviral drugs is increasing through positive evolutionary selection, with researchers documenting the trend in more than 30 percent of the samples tested.

The avian flu, an Influenza A subtype dubbed H5N1, is evolving a resistance to a group of antiviral drugs known as adamantanes, one of two classes of antiviral drugs used to prevent and treat flu symptoms, said CU-Boulder doctoral student Andrew Hill, lead study author. The rise of resistance to adamantanes -- which include the nonprescription drugs amantadine and rimantadane -- appears to be linked to Chinese farmers adding the drugs to chicken feed as a flu preventative, according to a 2008 paper by researchers from China Agricultural University, said Hill.

In contrast, resistance of the avian flu virus to the second, newer class of antiviral drugs that includes oseltamivir -- a prescription drug marketed under the brand name Tamiflu -- is present, but is not yet prevalent or under positive genetic selection, said Hill of CU-Boulder's ecology and evolutionary biology department. The CU findings should help health administrators around the world plan for the possibility of an avian flu pandemic.

The CU-Boulder study is the first to show H5N1 drug resistance to adamantanes arose through novel genetic mutations rather than an exchange of RNA segments within cells, a process known as re-assortment, said Hill. The research on the mutations, combined with molecular evolution tests and a geographic visualization technique using Google Earth, "provides a framework for analysis of globally distributed data to monitor the evolution of drug resistance," said Hill.

The CU-Boulder-led study appears online in the journal Infection, Genetics and Evolution. Co-authors included CU-Boulder Associate Professor Robert Guralnick, recent CU-Boulder graduate Meredith Wils
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