Travelers going to malarial regions should see their doctor before they start.进入疟疾流行地区的旅行者出发前应该先去看一下医生。Clouds of malarial mosquitoes rise from the swampy banks of the river Euphrates.一片片黑压压的疟蚊从幼发拉底河两岸的沼泽地升起。Anti-malarial vaccines are now undergoing trials.抗疟疾的疫苗正在试验阶段。