BERLIN Germany's federal agency for infectious diseases said on Tuesday there were signs the H1N1 swine flu virus had started to mutate and warned it could spread in the coming months in a more aggressive form.
Experts were concerned about how the flu was developing in Australia and South America, said Joerg Hacker, head of the Robert Koch Institute for infectious diseases.
"It's possible the virus has mutated. In autumn the mutated form could spread to the northern hemisphere and back to Germany," Hacker told a news conference in Berlin.
The World Health Organization raised swine flu to pandemic status earlier this month. According to its latest figures, more than 230 people have been killed by the flu worldwide from 52,000 confirmed cases, mostly in the United States and Mexico.
Symptoms of swine flu are typically fairly mild, but doctors have said the virus could evolve into something more aggressive.
According to WHO figures, Germany has the third highest rate of swine flu infection in Europe with 275 confirmed cases.
German Chancellor Angela Merkel told the conference that Germany was as prepared as it could be for any surge in cases.
"We are in contact about it internationally," she said. "Now all we have to do is coordinate internationally who should be vaccinated and how we should do it, in case things get worse."
The WHO has advised governments to prepare for a long-term battle against the new pandemic it officially calls A(H1N1).
WHO Director-General Dr. Margaret Chan said recently the virus is currently "pretty stable," but warned it could still change into a more deadly form, perhaps mixing with the H5N1 bird flu virus circulating widely in poultry.
(For latest WHO figures please go to here)
(Reporting by Marc Jones, editing by Mark Trevelyan)