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Article
- West Nile Virus Update
Extracted
from the "Clinical Nursing Resources" Newsletter, Volume
1, Number 16
The
West Nile virus (WNV) was first documented in Uganda in 1937. For
years, WNV was only found in the Eastern hemisphere, especially
in Africa. WNV was first identified in the United States
in New York City in 1999. Additional cases are identified and deaths
are reported daily.
Mosquitoes
transmit WNV when they bite humans. They also pass the virus to
birds (especially crows), horses, and smaller animals.
The virus is particularly virulent in birds. Humans do
not contract WNV by handling birds who have succumbed to it. They
must be bitten by an infected mosquito. The more bites, the
more exposure.
Horses
and small animals have relatively low levels of the virus
and do not transmit the disease. The incubation period of
WNV is from three to 14 days.
SYMPTOMS
The
WNV travels through the blood-brain barrier and can cause
viral encephalitis, meningitis, or both. Most victims experience
no symptoms or mild flu-like symptoms: Fever, headache,
anorexia, nausea and vomiting, myalagia, eye pain, rash,
and enlarged lymph glands.
WNV
affects all races and men and women equally. The illness lasts
three to six days. The elderly, chronically ill, or immunosuppressed
are more likely to become seriously ill or die
from WNV.
Symptoms
of viral encephalitis include confusion and a decreased
level of consciousness. Symptoms of viral meningitis include a stiff
neck, a positive Kernig sign, or a positive Brudzinski
sign. Both the Kernig sign and the Brudzinski sign are tests
of meningitis.
To
perform the Kernig sign, flex the person's thigh and extend the leg
at the knee. If the patient resists or complains of pain,
the sign is positive.
To
perform the Brudzinski sign, flex one of the person's legs. The sign
is positive if the other leg flexes on its own. In another
version, bending the person's head down results in flexion
of one or both of the hips, knees, or ankles.
LABORATORY
TESTS
The
following tests are used to diagnose WNV:
-
igM
antibody-capture ELISA test - to detect antibodies to
WVN in the serum or cerebrospinal fluid. The WNV antibody
remains in the body for about six months.
-
Identification
of the West Nile virus in the blood.
-
Lymphocytopenia,
anemia, and an elevated cerebrospinal fluid
protein. Note that false positives are possible in these tests
since the virus is related to similar diseases, such as St.
Louis encephalitis.
A
case is considered to be "probable WNV" when the WNV
antibody is identified and "confirmed WNV" when the virus
itself is identified.
TREATMENT
The
treatment is entirely supportive. Patients with mild cases are urged
to drink fluids, get plenty of rest, and take antipyretics.
Those who end up with encephalitis or meningitis often require
intensive care, antiseizure medications, mechanical ventilation, and
fluids and electrolytes.
PREVENTION
Urge
the public to
-
Drain
any collections of stagnant water found in the environment.
-
Use
mosquito repellants when they are outside. The strength should
be no more than 10% (DEET) for children and 10-50% for adults.
Treat clothing, skin, bedding, tents and tent screens. Avoid
getting mosquito repellant on the hands to prevent getting any
into the mouth, eyes, ears.
-
Wear
long sleeves and long pants.
-
Avoid
wearing bright colors or using perfumes. Both may attract
mosquitoes.
-
Stay
indoors from dusk to dawn, when mosquitoes are more active.
-
Report
dead birds to state and local health departments.
Governments
are spraying two types of chemicals on mosquito-
infested
areas:
-
Natural
larvocides, such as is Bacillus thuringiensis var. israelensis or
Bacillus sphericus.
-
Methoprine
to kill adult mosquitoes, which can cause eye irritations
or skin rash, though the incidence is rare.
BIBLIOGRAPHY
Centers
for Disease Control (2002). Prevention: Avoid mosquito bites
to avoid infection. Retrieved August 12, 2002. http://www.cdc.gov/ncidod/dvbid/westnile/index.htm.
Cunha,
B.A. (2002). West Nile encephalitis. Retrieved September 15,
2002. http://www.emedicine.com/med/topic3160.htm.
(Requires free
registration to access).
Petersen,
L.R., & Marfin, A.A. (2002). West Nile virus: A primer for
the clinician. Annals of Internal Medicine(137), 173-179.
Summary
by Becky Sisk, PhD, RN (c) December, 2002
Students:
Consider this a secondary source for information about WNV. Go
to the primary sources on this page to find references for your
paper or preparation. |
