Swine flu may become resistant to Tamiflu : International

Washington, March 2 - If the behaviour of the seasonal form of the H1N1 influenza virus is any indication, scientists say chances are high that most strains of the pandemic swine flu virus will become resistant to Tamiflu, the main drug stockpiled for use against it.

Researchers at Ohio State University - have traced the evolutionary history of the seasonal H1N1 influenza virus, which first infected humans during the 1918 pandemic.

It is one of three seasonal influenza A viruses that commonly infect humans. The others are H1N2 and H3N2.

Within H1N1, two strains of virus circulate in humans: a seasonal form and the pandemic form of influenza, known as swine flu, which has sickened millions and killed thousands of people since it first emerged in North America last spring.

Over time, the H1N1 strain of seasonal influenza has developed mutations that have caused it to become resistant to oseltamivir-based agents. Tamiflu is the brand name for oseltamivir phosphate.

'Something happened in 2008, when drug resistance took hold,' said Daniel Janies, associate professor of biomedical informatics at OSU, who led the study.

'The drug-resistant isolates became the ones that survived all over the world. This is just static now. The seasonal H1N1 influenza virus is fixed at resistant,' he said.

Janies and his colleagues have traced the history of the same mutation in the pandemic H1N1 strain of the virus as well, with data from its emergence last spring until December 2009.

And they are starting to see the same kinds of mutation in this virus - changes to an amino acid that allow the virus to resist the effects of oseltamivir - that they saw in the seasonal H1N1 flu.

'It is a pretty good bet that whatever pressure is in the environment, excessive use of Tamiflu or something else that was driving seasonal influenza to become resistant to Tamiflu is also going to apply to pandemic influenza,' Janies said. 'We can see it happening already.

'This has potential to indicate that we are going to have to think of something else to use to treat pandemic H1N1 influenza,' he added.