|
>
Department >
Home >
Equine
Equine Sciences Extension
Program
West Nile Virus
Background
West Nile
virus (WNV) is a mosquito-borne disease that was first
isolated in 1937 from the blood of a woman in the West
Nile district of Uganda. Since then, the WNV has been
commonly found in humans and birds and other vertebrates
in Africa, Eastern Europe, West Asia, and the Middle
East. The WNV first appeared in the United States in
1999 in New York City and has continued to spread throughout
the United States.
West Nile virus belongs to a group of single-stranded
RNA viruses called Flaviviridae whose members include
Japanese encephalitis virus, St. Louis encephalitis
virus, yellow fever virus and dengue fever virus. St.
Louis encephalitis is not new to the United States.
It first appeared in St. Louis, Missouri, in 1933, and
is the most common mosquito-transmitted disease in the
United States.
Clinical outcomes in people infected with WNV depend
upon the level of background immunity in the geographic
location. For example, in Egypt the WNV infection is
common in children, in which it causes a mild fever
illness. Following infection, antibodies and "memory"
white blood cells (T-lymphocytes) remain in the body
to provide future protection from the virus. It is assumed
that immunity will be lifelong; however, it may wane
in later years. There is no scientific evidence indicating
that people can be chronically infected with WNV.
|
