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)