Cover photograph (Copyright © 2006, American Society for Microbiology. All Rights Reserved.): The head of a male Culex pipiens pipiens mosquito is shown together with an atomic model of West Nile virus. The Culex mosquito is the principal vector that carries West Nile virus from host to host. The atomic model is based on the crystal structure of the major envelope glycoprotein E. The packing of E molecules on the viral surface is derived from a cryoelectron microscopy image reconstruction of dengue virus type 2 (W. Zhang et al., Nat. Struct. Biol. 10:907-912, 2003). (Photograph by Karine Delroux, Yale Medical School, New Haven, Conn.) (See related article on page 11000.)