The Irish Examinerreports that Dr. Chan, an expert from the WHO, believes H5N1 bird flu could be a bigger challenge than AIDS. If it mutates and spread rapidly from human to human it could threaten governments and economies.
Dr Chan told over 30 experts in Geneva that the agency's top priority was to keep the deadly H5N1 strain of bird flu from mutating.
"Should this effort fail, we want to ensure that measures are in place to mitigate the high levels of morbidity, mortality and social and economic disruption that a pandemic can bring to this world," she said.
WHO says 175 people are confirmed to have caught bird flu, and 95 of them have died.
Global influenza pandemics - as opposed to annual recurrences of seasonal flu - tend to strike periodically. In the 20th century, there were pandemics in 1918, 1957 and 1968.
Bird flu could potentially cause more deaths than those from the global flu pandemics. Because the H5N1 virus is airborne, it is easier to transmit and more contagious than HIV/AIDS, WHO officials said.
Another WHO expert, Dr Mike Ryan, director of epidemic and pandemic alert, said, "We truly feel that this present threat is likely to stretch our global systems to the point of collapse." H5N1 has continued to spread easily from country to country and scientists are sounding more alarmist with each new human case and with each discovery of the virus in a new country.