The West Nile Virus is one of a group of disease-causing viruses called flaviviruses, which are spread by insects, usually mosquitoes.  Other flaviviruses include yellow fever, dengue, and St. Louis encephalitis viruses.  The West Nile virus primarily circulates between infected birds and mosquitoes that bite them.  Only female mosquitoes bite and feed on blood; males feed on nectar.  The infected mosquitoes can transmit the virus when they bite other animals or people.

More than 130 species of birds have been reported to be infected with the West Nile virus, according to the CDC.  The virus also can infect horses and some other animals.  Even where the West Nile virus is circulating, not all mosquitoes become infected with it, and human infection does not occur in all individuals exposed to mosquitoes.

Below is from the CDC:

Family: Flaviviridae
Genus: Flavivirus Japanese Encephalitis Antigenic Complex
Complex includes: Alfuy, Cacipacore, Japanese encephalitis, Koutango, Kunjin, Murray Valley encephalitis, St. Louis encephalitis, Rocio, Stratford, Usutu, West Nile, and Yaounde viruses.
Flaviviruses: share a common size (40-60nm), symmetry (enveloped, icosahedral nucleocapsid), nucleic acid (positive-sense, single stranded RNA approximately 10,000-11,000 bases), and appearance in the electron microscope. Therefore, images of West Nile virus are representative for this group of viruses.
 

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Prepared for BIOG 154 Microscopic World -- Dr. Harry Kestler
Lorain County Community College -- Last modified: 04/18/03 -- Don't click here.