Dec. 10 (Bloomberg) -- Global climate change may have unexpected consequences on human health, including the spread of diseases such as malaria in the U.S., said Margaret Chan, director-general of the World Health Organization.

Countries must work together ``to mitigate climate change on a sufficient scale until countries unite behind an agreed-upon policy,'' said Chan, a doctor from China, in a lecture today at the National Institutes of Health in Bethesda, Maryland.

Delegates from about 200 countries are currently meeting on the Indonesian island of Bali to negotiate a treaty to limit emissions that contribute to warming when the Kyoto Protocol expires in five years. While Chan said ``the polar bear has been the poster child for climate change,'' she urged more attention to the potential risks for people.

``What would happen if rising temperatures accelerate the lifecycle of parasites? What will happen if malaria spreads to new areas?'' Chan asked. ``The U.S. doesn't have malaria. What if temperature continues to rise?''

Chan took office in January as head of WHO, an agency of the United Nations. She is a former director of health in Hong Kong, where she led efforts to combat the 2003 epidemic of severe acute respiratory syndrome, or SARS.

``I will never forget that agony of uncertainty: What microscopic beast has invaded our hospital system?'' she said. ``Then and in the future, nurses and doctors will be at the front lines.''

Chan delivered the seventh annual David E. Barmes Global Health Lecture. The event honors Barmes, a WHO employee and global health spokesman, who died in 2001.

To contact the reporter on this story: Emily Brown in Washington at ebrown18@bloomberg.net.

Last Updated: December 10, 2007 17:06 EST