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Mosquito-borne Encephalitis Virus Detected in Three Texas Counties
St. Louis encephalitis (SLE) virus has been
detected in mosquitoes collected in Harris
County and El Paso County. Eastern
equine encephalomyelitis (EEE) has been
confirmed in a Henderson County horse.
SLE and EEE are two of several mosquito-
borne viral diseases that occur in Texas.
SLE usually occurs in the eastern part of
the state from July through October.
During the last 10 years there have been
five SLE outbreaks, occurring in 1990-
1993 and 1995); the number of cases in
each outbreak ranged from 7 to 42. Spo-
radic cases were reported in 1994, 1996,
1998, and 2000; the number of confirmed
cases ranged from 1 to 4. No cases were
confirmed in 1997 and 1999. No cases of
human EEE have been reported in Texas
during the last 20 years.
Disease severity for both SLE and EEE
ranges from asymptomatic to fatal.
Patients with mild illness often have fever
and headache or viral (aseptic) meningi-
tis; those with more severe infections
have headache, high fever, meningeal
signs, disorientation, stupor, coma, trem-
ors, and convulsions. Infection can result
in long-term neurologic sequelae. Most
SLE cases are aymptomatic; less than
10% of symptomatic cases result in death.
As mentioned, EEE is uncommon.
However, when diagnosed, cases are most
often in children or the elderly.
Approximately 30% of symptomatic
EEE cases are fatal.
Specimens for virus isolation and
serologic SLE or EEE testing may be
submitted with completed G-1 A and/or
B forms to the Texas Department of
Health Laboratory, 1100 W 49th Street,
Austin, TX 78756.
For virus isolation: CSF must be placed
on dry ice and shipped overnight. Brain
tissue should be submitted with prior no-
tification and shipped cold but unfrozen
(ie, on wet ice). Please call the laboratory
at 512/458-7515 prior to shipment of
these specimens.
For serologic testing: CSF and/or serum
may be submitted. Single serum speci-
mens are tested, but paired sera collected
10 to 14 days apart are preferred. (The
pairing of sera enables the detection of an
antibody titer rise, with a fourfold rise in-
dicating a current infection). Specimens
for serologic testing may be shipped at
room temperature.
Mosquito-borne encephalitis is a notifiable condition
in Texas. Report suspect cases by calling 800/705-8868 or
800/252-8239. For more information call 512/458-7228.
Two Primary Amebic Meningoencphalitis Deaths this Month
Reports this month of 2 deaths from
primary amebic meningoencephalitis
(PAM) prompted the Texas Department
of Health (TDH) to issue a warning about
swimming in lakes, rivers, and stagnant
water. The children who died had been
swimming in lakes in northeast Texas.
PAM is a fulminant, purulent infection of
the gray matter of the brain. The caus-
ative organism, Naegleria fowleri, is a
ubiquitous, free-living ameba that thrives
in fresh water that is warm (usually
> 800F), particularly if it is stagnant or
slow moving. It is found in almost all
soil and untreated surface water.
Activities such as skiing and jumping into
the water may increase a swimmer's risk
of infection. It is hypothesized that such
activities can force the organisms into the
nasal passages, giving the amebae easy
access to the brain and spinal cord.
Symptoms of the infection include severe
headache, high fever, meningismus, nausea,
vomiting, seizures and hallucinations or
other mental status changes. On presenta-
tion patients typically have an elevated
white count with a left shift. Cerebral
spinal fluid findings in one series of 6
patients included pleocystosis (range 450-
4,400) with a predominance of polymor-
phonuclear cells, hypoglycorrhachia
(40< mg/dL), and elevated protein lev-
els (>250 mg/dL).1
Diagnosis can be made by demonstration
of the amebae in cerebrospinal fluid (CSF)
or biopsy specimens. Motile trophozoites
may be observed on a direct wet mount,
Continued
DPN
Page 5
Vol. 61 No. 18