 Nearly 200 infections now confirmed in New York and New Jersey alone. More than 2,500 across the U.S. and Puerto Rico, five times higher than this time last year. Transmission occurs when someone is bitten by an infected mosquito. Experts say with higher temperatures and higher rainfall amounts, mosquitoes that carry dengue viruses are extending their range. Mosquitoes love warm weather, so over time we are starting to see dengue spread in mosquitoes more northward.