Mosquitoes are kept in a test tube at the Center for Vaccine Development, Thursday, June 14, 2012, at Mahidol University, in Nakhonpathom, outside Bangkok. Dengue is a threat to nearly 3 billion people and a health priority in many countries of Latin America and Asia where epidemics occur. It is also one of the leading causes of fever among travelers to endemic areas. (Patrick de Noirmont/Sanofi Pasteur)