Definition of LaCrosse encephalitis
< b>LaCrosse encephalitis: One of the main types of encephalitis caused by
an arbovirus in the US. An arbovirus is a virus that is arthropod-borne (carried
by a mosquito, tick or another kind of arthropod). The arbovirus infects and inflames
the brain.
LaCrosse (LAC) encephalitis was first found in a 4-year-old in LaCrosse, Wisconsin
in 1963. Since then, the virus has been identified in a number of Midwestern and
Mid-Atlantic states. During an average year, about 75 cases of LAC encephalitis
are reported to the CDC. However, the cases that are reported are probably just
the tip of a much larger iceberg.
Historically, most cases of LAC encephalitis were found in upper Midwestern states
(Minnesota, Wisconsin, Iowa, Illinois, Indiana, and Ohio). Recently, more cases
have been found in mid-Atlantic (West Virginia, Virginia and North Carolina) and
southeastern (Alabama and Mississippi) states. It has long been suspected that LAC
encephalitis has a broader distribution and a higher incidence in the eastern United
States, but is underreported there because the virus is often not specifically identified.
Most cases of LAC encephalitis occur in children under 16 years of age. The virus
is a "zoonotic pathogen" that is cycled between the daytime-biting treehole mosquito
(Aedes triseriatus) and vertebrate amplifier hosts (chipmunks, tree squirrels) living
in deciduous forest habitats. The virus is maintained over the winter by transovarial
transmission through mosquito eggs. If the female mosquito is infected, she may
lay eggs that carry the virus, and the adults coming from those eggs may be able
to transmit the virus to chipmunks and to humans.
LAC encephalitis initially presents as a nonspecific summertime illness with
fever, headache, nausea, vomiting and lethargy. Severe disease occurs most commonly
in children under the age of 16 and is characterized by seizures, coma, paralysis,
and a variety of neurological sequelae after recovery. Death from LAC encephalitis
occurs in less than 1% of clinical cases. In many clinical settings, cases of LAC
encephalitis are reported as aseptic meningitis or viral encephalitis of unknown
etiology.
LAC encephalitis in children can leave lingering sequelae such as poor balance,
memory difficulties and speech problems. In children over 5 who had a severe case
of LaCrosse disease, over a half had signs of attention-deficit/hyperactivity disorder
a year after they left the hospital and nearly a third had borderline intelligence
or mental retardation, according to a report in The New England Journal of Medicine
(March 15, 2001).
To avoid contracting the LAC virus, children should ideally stay away from areas
where mosquitos live, wear insect repellent and long sleeves, and avoid walking
in the early morning and early evening when mosquitos are most active. These precautions,
while wise, may not be easy for parents to enforce.
For more information, see Arbovirus encephalitis.
Common Misspellings: lacrosse ensephilitis, lacrosse insephilitis
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