U.S. Becomes More Vulnerable to Tropical Diseases Like Zika. Zika Virus, McNeil, Donald G Jr, Global Warming, Epidemics, Mosquitoes, Ticks (Insects), Dengue Fever, Lyme Disease, Chikungunya Virus, West Nile Virus, Rocky Mountain Spotted Fever, Viruses, Birth Defects, Centers for Disease Control and Prevention, Brazil, Florida, United States