West_Nile_virus_transmission_cycle

“West Nile virus transmission cycle” by Centers for Disease Control and Prevention – http://www.cdc.gov/ncidod/dvbid/westnile/cycle.htm. Licensed under Public Domain via Wikimedia Commons – http://commons.wikimedia.org/wiki/File:West_Nile_virus_transmission_cycle.jpg#mediaviewer/File:West_Nile_virus_transmission_cycle.jpg