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Encephalitis, Arboviral
1995 Case Definition
Clinical description
Arboviral infection may result in a febrile illness of
variable severity associated with neurologic symptoms ranging from headache
to aseptic meningitis or encephalitis. Arboviral encephalitis cannot
be distinguished clinically from other central nervous system infections.
Symptoms may include headache; confusion or other alteration in sensorium;
nausea; or vomiting. Signs may include fever, meningismus, cranial nerve
palsies, paresis or paralysis, sensory deficits, altered reflexes, convulsions,
abnormal movements, and coma of varying degree.
Laboratory criteria for diagnosis
- Four-fold or greater change in serum antibody titer,
or
- Isolation of virus from or demonstration of viral
antigen or genomic sequences in tissue, blood, cerebrospinal fluid
(CSF), or other body fluid, or
- Specific IgM antibody in CSF
Case classification
Probable: a clinically
compatible illness occurring during a period when arboviral transmission
is likely, and with the following supportive serology: a stable (less
than two-fold change) elevated antibody titer to an arbovirus (e.g.,
greater than 320 by hemagglutination inhibition, greater than 128 by
complement fixation, greater than 256 by immunofluorescence, and greater
than160 by neutralization), or a positive serologic result by enzyme
immunoassay (EIA).
Confirmed: a clinically compatible illness
that is laboratory confirmed
Comment
The seasonality of arboviral transmission is variable
and depends on the geographic location of exposure, the specific cycles
of viral transmission, and local climatic conditions. Reporting should
be etiology specific (see below--those in bold are nationally reportable
to CDC):
- St. Louis encephalitis
- Western equine encephalitis
- Eastern equine encephalitis
- California encephalitis (includes
infections from the following viruses: LaCrosse, Jamestown Canyon,
Snowshoe Hare, Trivittatus, Keystone, and California encephalitis
viruses)
- Powassan encephalitis
- Other central nervous system infections transmitted
by mosquitoes, ticks, or midges (e.g. Venezuelan equine encephalitis,
Cache Valley encephalitis)
See also:
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