West Nile Virus (WNV) is an arbovirus that can cause illness in humans,
including encephalitis (inflammation of the brain). Mosquitos get the virus
by feeding on infected birds and can then pass it on to other birds, and
occasionally to other animals and people. The virus is not spread
person-to-person.
An arboviral encephalitis is a viral infectious disease affecting the brain
that is transmitted by a mosquito or other insect vector. The virus attacks
the brain, causing inflammation and swelling. Arboviruses belong to several
groups of viruses that usually infect birds and are transmitted from
bird-to-bird by mosquitos. The name "ar-bo-virus" comes from the fact that
they are transmitted by arthropods (insects and other "bugs"). WNV is caused
by a specific type of arbovirus known as a flavivirus, which was found
previously only in Africa, eastern Europe and west Asia. WNV is closely
related to other arboviruses such as St. Louis Encephalities (SLE), found in
the U.S., Japanese Encephalities, found in southeast Asia, and Murray Valley
Fever, found in Australia and New Guinea. In the U.S., WNV cases are most
prevalent in late summer and early autumn; in Nevada, mosquito season is
typically April through October.
West Nile Virus Background and History in Nevada
Prior to 1999, no WNV cases had been reported in the United States, although
the virus had a wide distribution in Africa, Asia, the middle east and
Europe and caused occasional epidemics. In 1999, the virus appeared in New
York City, and was responsible for an encephalitis outbreak causing 62 human
cases and seven deaths.
Between 1999 and 2003, WNV expanded from the northeastern U.S. to the south
central states and westward, appearing on the west coast for the first time
in 2002. Across the U.S., the number of human WNV cases in 2002 increased
dramatically and greatly expanded in geographic range (4,161 reported cases
with 277 deaths). The 2002 epidemic was the largest WNV epidemic ever
reported and the largest of any reported arboviral encephalitis epidemic in
the Western Hemisphere.
In 2003, WNV activity continued to increase, and was reprted in 48 states
and the District of Columbia. Today, WNV is firmly established throughout
most of the US.
WNV was first detected in Nevada in 2004, and has been reported in all
counties.
For more information about the West Nile Virus, click here
