Researchers from the California Institute of Technology and Purdue University have determined the structure of the virus that causes dengue fever, which could lead to the creation of a vaccine, according to a report in journal Cell by Caltech biology professor James Strauss, lead author Richard Kuhn of Purdue, and Michael Rossman and Timothy Baker of Purdue. The researchers obtained the structure using a cryoelectron microscope, and for the first time scientists have an electron-density map that shows the spherical layers covering the RNA core of a flavivirus, a family that includes diseases such as yellow fever, West Nile, and Japanese encephalititis virus. Dengue fever is spread by mosquitoes and causes 20,000 deaths annually.