This digitally colorized transmission electron microscopic (TEM) image depicts numerous Chikungunya virus particles, which are composed of a central dense core that is surrounded by a viral envelope. Each virion is approximately 50nm in diameter (image by Cynthia Goldsmith, Centers for Disease Control and Prevention, USA; Public Health Image Library, image ID #17550); image modified by MIC. The cover is published under the Creative Commons Attribution (CC BY) license.