UNITED NATIONS, Sha'ban 04, 1437, May 11, 2016, SPA -- The World Health Organization (WHO) said that a major yellow fever outbreak in Angola and two smaller flare-ups in Uganda and Congo largely are under control but countries have been warned to be vigilant in case the disease appears elsewhere. Yellow fever is transmitted by mosquitos, which have flourished during the abnormal El Nino weather of the past year caused by the warming of the Pacific Ocean off the coast of South America. "What we hope is that El Nino will not be faster than we are," said Sylvie Briand, head of WHO's department of pandemic and epidemic diseases. "We are concerned for other countries that have high densities of mosquitoes." Until the development of the highly effective vaccine, Briand said, yellow fever changed history, with outbreaks delaying construction of the Panama Canal and encouraging Napoleon to give up territorial ambitions in North America. --SPA 14:08 LOCAL TIME 11:08 GMT www.spa.gov.sa/w