AN INFLUENZA virus similar to swine flu has mutated and strains are now emerging globally that are resistant to the frontline drug treatment Tamiflu.
Similar resistance has also been seen in patients with swine flu where resistance to antiviral treatment can emerge in less than two weeks.
The antiviral drugs Tamiflu (oseltamivir) and Relenza (zanamivir) are a key part of the Government’s response should a swine flu pandemic emerge here. Now scientists in California have shown how the ordinary or “seasonal” form of the H1N1 flu can become resistant to antivirals.
The group, led by Nobel Prize winner Prof David Baltimore of the California Institute of Technology, showed how a number of mutations have helped the seasonal H1N1 to survive treatment with these drugs. They publish their findings this morning in the journal Science.
The key mutation, known as H274Y, is not new and has been known for a decade, Prof Baltimore said. Viral strains with it are able to survive treatment with Tamiflu, but having the mutation also meant they replicated poorly and were not easily transmitted, which meant they “were not of great clinical significance”.
But during the 2007-2008 flu season, forms of H1N1 carrying the the mutation began cropping up all over the world, showing powerful drug resistance but also the ability to spread across a population, the researchers said.
By the following season, virtually all seasonal H1N1 had become resistant to Tamiflu.
“Something happened to make the Tamiflu-resistant virus also capable of replicating and spreading like wild-type flu viruses,” said Dr Jesse Bloom, joint leader on the research.
The researchers studied the genetic blueprint of the virus and found two new mutations. These allowed it to spread and replicate readily while retaining drug resistance. So far the H274Y mutation has not become widespread in the avian flu (H5N1) or the swine flu (novel H1N1), they report. They believe their discoveries may help to show how the H274Y mutation could enter these strains, however.
Tamiflu resistance has already been seen in swine flu patients under certain conditions. The US National Institutes of Health reported last March on the cases of two immune-compromised patients who did not respond quickly to antiviral treatment.
After less than two weeks, both patients developed resistance to two of the best antiviral treatments available, including Tamiflu.
While the emergence of drug-resistant flu strains was not surprising, the speed with which this could happen was noteworthy, said institute director Dr Anthony Fauci.
Separately, the World Health Organisation said yesterday the H1N1 pandemic was not over, although its most intense activity had passed in much of the world. The WHO emergency committee said it remained critical for countries to maintain vigilance.