Bird flu becoming resistant to antiviral drugs

New research suggests that bird, or avian, flu is becoming more resistant to antiviral drugs, so say researchers at the University of Colorado at Boulder.

Andrew Hill and colleagues found that more than 30% of samples of the avian flu virus (influenza A subtype H5N1) were resistant to adamantanes, one of the two classes of antiviral drugs available to prevent and treat the infection. The researchers say that it is thought that the rise in resistance to adamantanes, which include the non-prescription drugs amantadine and rimantadane, has been caused by Chinese farmers adding the drugs to chicken feed in an attempt to prevent their livestock from getting the disease.

The researchers add that resistance to the other class of antiviral drugs that can be used to combat avian flu, which includes oseltamivir – better known as Tamiflu, is present, but not prevalent.

"As these adamantanes have gotten into nonhuman vectors like birds, the positive selection for resistance to avian flu is rising. If Tamiflu is ever used in the manner of adamantanes, we could conceivably see a similar resistance developing through positive selection,” warned Hill.

The CDC estimates that an avian flu pandemic is likely to infect 15-35% of the US population, kill millions of citizens, and cost the economy in excess of $100 billion.

News release: Avian flu becoming more resistant to antiviral drugs, says University of Colorado study. University of Colorado at Boulder. January 7th 2009.