 Health experts say now is the time for us to invest in bug spray. A rise in West Nile virus cases coupled with a new warning this week about dengue fever has experts worried that other mosquito-borne illnesses will start popping up. We're talking yellow fever and Zika. It's a combination of warming temperatures due to climate change, also urbanization. Baylor's Dr. Peter Hotez, who heads the School of Tropical Medicine, has been coordinating with the White House's Office of Pandemic Preparedness. He fears a rash of dangerous cases could overwhelm rural health systems.