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 (CNS) infections. Symptoms can include headache,
confusion or other alteration in sensorium, nausea, and 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
Fourfold 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 immunoglobulin M (IgM) antibody by enzyme immunoassay
(EIA) antibody captured in CSF or serum. Serum IgM antibodies alone should
be confirmed by demonstration of immunoglobulin G antibodies by another serologic
assay (e.g., neutralization or hemagglutination inhibition).
Case classification
Probable: a clinically compatible
case occurring during a period when arboviral transmission is likely, and with
the following supportive serology: a stable (less than or equal to twofold change)
elevated antibody titer to an arbovirus (e.g., greater than or equal to 320 by
hemagglutination inhibition, greater than or equal to 128 by complement fixation,
greater than or equal to 256 by immunofluorescence, and greater than or equal
to 160 by neutralization, or greater than or equal to 400 by enzyme immunoassay
IgM).
Confirmed: a clinically compatible case 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;
the four encephalitides printed 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
West Nile encephalitis
Other CNS infections transmitted by mosquitoes, ticks, or
midges (e.g., Venezuelan equine encephalitis and Cache Valley encephalitis)