"It really is all of humanity that is under threat during a pandemic, " said Dr. Margaret Chan, the WHO's director-general.

CNN: Confirmed swine flu cases leap

Dr Margaret Chan, Director-General of the WHO, said these ancient diseases were already being "brought to their knees with stunning speed".

BBC: Plan to cut burden of tropical disease

Dr. Margaret Chan, the U.N. agency's director-general, said the decision to raise the alert on the 6-point scale indicated that all countries should "immediately" activate pandemic preparedness plans.

CNN: WHO raises pandemic alert to second-highest level