LONDON, Oct 6 (Reuters) - Dengue fever will become a major threat in the southern United States, southern Europe and new parts of Africa this decade, the WHO's chief scientist said, as warmer temperatures create the conditions for the mosquitoes carrying the infection to spread.

The illness has long been a scourge in much of Asia and Latin America, causing an estimated 20,000 deaths each year. Rates of the disease have already risen eight-fold globally since 2000, driven largely by climate change as well as the increased movement of people and urbanization.