Health officials tell US doctors to be alert for dengue as cases ramp up worldwide

U.S. health officials are warning doctors to be alert for dengue cases as the tropical disease breaks international records. Dengue is spread by mosquitoes and it has been surging worldwide, helped by climate change. The virus remains less common in the continental United States, but in the 50 states so far this year there have been three times more cases than at the same point last year. Most were infections that travelers got abroad. But officials warn of the growing threat locally acquired from the bites of U.S. mosquitoes. The Centers for Disease Control and Prevention issued a health alert to doctors on Tuesday.