Mutating viruses overtake medicine's best weapons

Resistance to anti-flu drugs has risen by 12 per cent worldwide in the past decade, and scientists are worried at the implications for health officials trying to avert a pandemic.

Researchers at the Centres for Disease Control and Prevention in Atlanta found resistance to a class of drugs used to treat influenza for more than 30 years rose from 0.4 per cent in 1994-1995 to 12.3 per cent last year.

In some countries in Asia, where scientists suspect the next strain of flu with pandemic potential will originate, drug resistance exceeded 70 per cent.

"Our report has broad implications for agencies and Governments planning to stockpile these drugs for epidemic and pandemic strains of influenza," said Dr Rick Bright of the CDC.

The findings, which are reported online by The Lancet medical journal, suggest the drugs amantadine and rimantadine will probably no longer be effective for treatment or as a preventive in a pandemic outbreak of flu.

The drugs, known as adamantane derivatives, inhibit the replication of the influenza A virus.

But they do not work against influenza B viruses or the H5N1 strain of bird flu that has killed more than 60 people since late 2003.

Although it is not easily transmitted from person to person, public health officials fear the H5N1 strain could mutate and cause a worldwide pandemic.

The World Health Organisation recommends governments build stockpiles of an alternative class of drugs, neuraminidase inhibitors.

The CDC researchers said their study of 7000 influenza A viruses obtained worldwide was the largest and most comprehensive report on adamantane resistance to date.

They said their findings illustrated the importance of monitoring the rise of drug-resistant viruses, but they did not explain why there was an increase in resistance.

- REUTERS