|What Is West
Viruses and bacteria can cause
encephalitis (an inflammation of the
brain) in humans and other animals. West
Nile encephalitis is a mosquito-borne
infection of the brain caused by West
Nile virus (WNV), a close relative of
St. Louis encephalitis virus. It is
thought to have been introduced into the
New York City area in 1999 and by 2003
had spread across the country to
California. WNV is commonly found in
Africa, West Asia and the Middle East.
Although it is not known how the virus
was introduced to the U.S., it may have
entered this country in an infected
traveler, bird or mosquito.
|How do people
get West Nile encephalitis?
People get West Nile encephalitis from
the bite of a mosquito (primarily the
Culex group of species) that is infected
with WNV. A mosquito becomes infected by
biting a bird that carries the virus.
WNV is not spread by person-to-person
contact or directly from birds to
common birds to carry West Nile
|Adult crows are
about 17 to 21 inches in
length, while juvenile
crows are about 10
inches in length, or
about the length of a
Juvenile crows have
Crows are all black,
beak, legs and feet. The
crow's nostrils are
covered with bristles.
|Blue jays are 10
inches long and have a
black sturdy bill and
blue crest. They have a
black eyeline and
breastband and a
greyish-white throat and
underparts. The wings
are bright blue with
black bars and white
patches. Blue jays have
a long blue tail with
black bars and white
corners. Their legs are
|When was West Nile
virus first detected in Illinois?
In September 2001 laboratory tests confirmed the
presence of West Nile virus in two dead crows
found in the Chicago area. The following year
all but two of the state's 102 counties reported
West Nile activity.
What about human cases of
West Nile disease in Illinois?
In August 2002, Illinois reported its first case
of West Nile disease and by the end of the year
had counted more human cases (884) and deaths
(67) than any other state in the nation. In
2003, the number of West Nile disease human
cases fell to 54 and only one death and in 2004,
there were 60 human cases and four deaths.
What is the transmission
cycle of West Nile virus in the environment?
Mosquitoes become infected with West Nile virus
when they feed on infected birds. These infected
mosquitoes then can transmit West Nile virus to
humans and to other birds and animals when a
mosquito bite occurs.
|Is it only humans who
become ill when infected with West Nile virus?
No. Certain animals also can become ill when
infected with West Nile virus. For example,
horses exposed to West Nile virus can develop
encephalitis. Also, certain birds – particularly
crows and blue jays – can become ill and die
with West Nile virus infection.
What are the symptoms of
West Nile disease? Most people who are
infected have no symptoms or may experience mild
illness, such as a fever and headache, before
fully recovering. In some individuals,
particularly the elderly, West Nile virus can
cause a serious disease that affects the brain
called West Nile encephalitis. It can cause
permanent neurological damage and be fatal.
Symptoms generally occur three to 15 days
following the bite of an infected mosquito and
range from a slight fever, headache, rash,
swollen nodes and conjunctivitis (irritation of
the eye) to the rapid onset of a severe
headache, high fever, stiff neck,
disorientation, muscle weakness, coma or death.
Less than 1 percent of persons infected with
West Nile virus will develop severe illness.
|Who is at risk of
contracting West Nile disease?
All residents in areas with West Nile
virus activity are at risk of getting West Nile
disease; those at highest risk of severe disease
are persons 50 years of age or older and those
whose immune systems are weakened by illness or
medical treatment (for example, chemotherapy).
Is there a treatment for
West Nile disease
There is no specific therapy for West
Nile encephalitis. In more severe cases,
intensive supportive therapy – hospitalization,
intravenous (IV) fluids, airway management,
respiratory support (ventilator) if needed,
prevention of secondary infections (pneumonia,
urinary tract, etc.) and good nursing care – are
|Is there a vaccine for
West Nile disease?
No human vaccine for West Nile virus disease
If I travel to an area
where birds with West Nile virus have been
reported and I am bitten by a mosquito, am I
likely to get sick?
No. Even in areas where mosquitoes do carry the
virus, very few mosquitoes (usually less than
one out of 500) are infected. The chance that
one mosquito bite will be from an infected
mosquito is very small.
If bitten by a mosquito,
should I be tested for West Nile virus?
No. Illnesses related to mosquito bites are
rare. However, you should see a doctor
immediately if you develop symptoms such as high
fever, confusion, muscle weakness or severe
headaches. Patients with mild symptoms are
likely to recover completely and do not require
any specific medication or laboratory testing.
|Why is the state
testing birds (especially crows) for West Nile
Crows appear to be highly sensitive to the virus
and provide an early warning system for
detecting West Nile virus activity in a
community. Knowledge of infected birds in a
neighborhood or community allows public health
officials to alert citizens about the increased
risk of mosquito-borne diseases.
What should I do if I find
a dead bird?
If a dead crow or blue jay is found between May
1 and the end of October and appears to have
died from natural causes, you should report this
information to your local health department.
Your local health department will let you know
if it is still collecting and testing dead
birds. If the local health department has
stopped collecting birds, you will be provided
with instructions on how to safely dispose of
What time of year are
mosquito viruses spread?
Viruses are most likely to be spread
during the warm weather months when mosquitoes
are most active, usually beginning in the spring
and lasting until the first hard frost. Most
human cases occur in late summer and fall.
|Are bird and wild game
hunters at risk for West Nile virus?
Because of their outdoor exposure, hunters may
be at risk if they are in areas with West Nile
virus activity and are bitten by mosquitoes. If
they anticipate being exposed to mosquitoes,
they should apply insect repellent to clothing
and skin, according to label instructions, to
prevent mosquito bites. Hunters should follow
the usual precautions when handling wild animals
and birds. They should wear gloves when handling
and cleaning birds or animals to prevent blood
exposure to bare hands.
Can a person contract West
Nile disease by eating infected game birds?
Proper cooking kills the West Nile virus.
Consequently, there is no danger associated with
eating wild game that might be infected.
Can West Nile disease be
The best way to prevent West Nile disease or any
other mosquito-borne illness is to reduce the
number of mosquitoes around your home and
neighborhood and to take personal precautions to
avoid mosquito bites. Here are some suggestions:
Avoid being outdoors when
mosquitoes are most active, especially
between dusk and dawn.
wear shoes and socks, long pants and a
long-sleeved shirt, and apply insect
repellent that includes DEET, picaridin or
oil of lemon eucalyptus according to label
instructions. Consult a physician before
using repellents on infants.
Make sure doors and windows
have tight-fitting screens. Repair or
replace screens that have tears or other
openings. Try to keep doors and windows
shut, especially at night.
Eliminate all sources of
standing water that can support mosquito
breeding, including water in bird baths,
ponds, flowerpots, wading pools, old tires
and any other receptacles. In communities
where there are organized mosquito control
programs, contact your municipal government
to report areas of stagnant water in
roadside ditches, flooded yards and similar
locations that may produce mosquitoes.
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