West Nile Virus

West Nile virus has emerged in recent years in temperate regions of Europe and North America, presenting a threat to public, equine, and animal health. The most serious manifestation of West Nile virus infection is fatal encephalitis (inflammation of the brain) in humans and horses, as well as mortality in certain domestic and wild birds.

The first appearance of West Nile virus in North America occurred in 1999, with encephalitis reported in humans and horses, and the subsequent spread in the United States. As of May 2006, West Nile virus has been documented in the contiguous United States and the District of Columbia.

Resources for the Public

General Information

Information and Images for Mosquito and Bird Identification

West Nile Bird Submission Identification Chart

History, Biology, and Public Health Control of Culex tarsalis (Mosquito)

Mosquito larvae (Image)

Video clips - mpeg format (Warning: these files are large)

Mosquito larvae collection (14MB) - Stagnate pools of water can act as breeding sites for the species of mosquitoes that harbor West Nile Virus. Many mosquito control districts monitor these areas as part of their control programs. This video shows a good mosquito breeding habitat and a mosquito control officer dip testing for mosquito larvae. The close up of the dipper reveals mosquito larvae and mosquito pupa.
Mosquito larvae under microscope (5MB) - This video shows a mosquito larva as it appears under a dissection microscope. In the end of the video clip, the head of the larva can be seen hanging down on the left and its dark breathing tube can be seen sticking up on the right.
Sideview of larvae under water (8MB) - In this video, two mosquito larvae can be seen hanging down from the surface of the water from their breathing tubes. Mosquito pupae can be seen on the far right and far left sides of the screen.

Adult Mosquito Control Information for the Public