West Nile virusArticle Free Pass West Nile virus, virus
belonging to the family Flaviviridae, related to viruses that
can cause yellow fever and dengue and more closely to viruses
that can cause encephalitis (inflammation of the brain).
Predominantly an infection of birds, West Nile virus is highly
fatal for many avian species (e.g., crows and other corvids). A
threat to human health occurs when infected birds are bitten by
mosquitoes, which then transmit the virus to humans. Most human
infections are inapparent or mild, causing a flulike illness
that usually lasts only a few days. However, in a minority of
infected persons, particularly in those over the age of 50, the
virus multiplies in the lymphoid tissue and circulates in the
bloodstream (possibly also multiplying in leukocytes, or white
blood cells) before reaching the brain, resulting in
encephalitis. Symptoms of West Nile encephalitis include
headache, fever, neck stiffness, disorientation, and muscle
weakness. Death may result. West Nile virus histor