West Virginia Department of Health and Human
Resources Information for Physicians –
West Nile Virus
What is West Nile virus?
West Nile is a flavivirus, and the causative agent
of a potentially lethal encephalitis that affects horses, birds, and
people.
What are the signs and symptoms of West Nile virus?
West Nile is most commonly recognized in patients
presenting with aseptic meningitis or encephalitis during the summer and
early fall. Other neurological manifestations may include ataxia and
extrapyramidal signs, cranial nerve abnormalities, myelitis, optic
neuritis, polyradiculitis, and seizures. The greatest risk factor for
severe neurological disease is advanced age.
West Nile fever is the mildest clinically recognized
form of the disease. Patients may present with sudden onset of fever,
malaise, gastrointestinal symptoms, eye pain, headache, myalgia, rash, and
lymphadenopathy. Duration of this self-limited illness is three to six
days.
Preliminary data from clinical investigations
conducted during the 2002 Arbovirus season are elucidating an expanding
spectrum of neurological disease. Emerging and evolving clinical syndromes
include: movement disorders, parkinsonism, rhabdomyolysis and acute
flaccid paralysis.
How can I make the diagnosis of West Nile virus?
Testing by the antibody capture enzyme-linked
immunosorbent assay (MAC-ELISA) is available free of charge through the
Office of Laboratory Services (OLS) at WVDHHR. Call 304-558-3530 to
arrange:
- The most efficient diagnostic method is
detection of IgM antibody to WNV in serum or cerebral spinal fluid (CSF)
collected within 8 days of illness onset using the IgM antibody
capture enzyme-linked immunosorbent assay (MAC-ELISA). Demonstration
of West Nile IgM antibody in the CSF by MAC-ELISA is diagnostic. All
specimens positive for WNV antibodies should be referred to OLS for
confirmation.
- Patients with specimens drawn within 7 days of
onset of symptoms that are found negative by MAC-ELISA should have a
convalescent specimen drawn at least two weeks later.
Due to the fact that IgM antibodies may persist for
greater than one year, residents in endemic areas may have persistent IgM
antibodies from a previous infection that is unrelated to their current
illness. Since West Nile virus was present in our state last year acute
and convalescent serum specimen collection and submission are recommended
to confirm acute infection.
- A four-fold rise in titer between acute and
convalescent serum is also diagnostic. Acute sera should be drawn
within seven days of onset, and convalescent sera should be drawn at
least 2 weeks later.
- Patients with encephalitis/meningitis should
also be tested for La Crosse encephalitis, eastern equine
encephalitis, and St. Louis encephalitis during arbovirus season.
Other laboratory clues include CSF abnormalities.
Elevated CSF WBC (range 0-1782 cells/mm3) with a lymphocytic
predominance has been described. Protein is universally elevated (51 to
899 mg/dL) and glucose is normal.
Peripheral WBC may be elevated and hyponatremia (Na
<135 mmol/L) may also occur. A few patients may have abnormalities of
bilirubin or transaminases.
Can West Nile virus infection be prevented?
Treatment is supportive, and there is no vaccine, so
prevention is key for this mosquito-borne disease. We are asking
physicians to be alert for this disease and report confirmed and suspect
cases to the local health department immediately. Advise all patients to
take the following precautions:
- Remove all old tires, containers, and any
item from the environment that can collect standing water and
serve as a mosquito breeding site.
- Empty and change the water in bird baths,
fountains, wading pools, rain barrels, and potted plant trays at
least once a week, if not more often.
- Drain or fill temporary pools with dirt.
- Keep swimming pools treated and circulating,
and rain gutters unclogged.
- Use mosquito repellents when necessary and
follow label directions and precautions closely.
- Use head nets, long sleeves, and long pants
if you venture into areas with high mosquito populations.
- Make sure window and door screens are
"bug tight."
Five additional routes of infection have become
apparent during the 2002 West Nile season. It is important to note that
these other methods of transmission represent a very small proportion of
cases. New modes of transmission are via: transplantation, transfusion,
breastfeeding, transplacental and occupational exposures (mostly
laboratory workers). (More information may be found on the CDC’s website
at: http://www.cdc.gov/ncidod/dvbid/westnile/clinical_guidance.htm
How can I get more information?
Patient education materials are available on the
West Virginia Infectious Disease Epidemiology Program’s website at: http://www.wvdhhr.org/bph/oehp/sdc/westnile.htm
Several clinical case series and reviews have
recently been published:
Ann Intern Med,
2002; 137:173-179.
Lancet Infect Dis,
2002; 2:519-529.
N Engl J Med,
2001; 344:1807-14.
Emerging Infectious Diseases, 2001;
7:654-658; and
Emerging Infectious Diseases, 2001;
7:675-678.
CDC maintains an excellent web-site at:
http://www.cdc.gov/ncidod/dvbid/westnile/index.htm
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