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Vol. 57 No. 13
Endemic Arboviral Activity
The arboviruses, a group of viruses transmitted
by arthropods (usually mosquitoes), are known
to produce clinical and subclinical illnesses in
humans. Illness can range in severity from
acute, benign fevers of short duration, to mild
aseptic meningitis, to encephalitis with coma
and death. Arboviral activity in Texas is usu-
ally limited to five diseases: California en-
cephalitis (CE), St. Louis encephalitis (SLE),
eastern equine encephalomyelitis (EEE), West-
ern equine encephalomyelitis (WEE), and den-
gue fever. In Texas these diseases occur during
the warmer months of the year.
From June through November of each year,
Texas health departments administer statewide
arboviral encephalitis surveillance programs to
detect virus activity in birds and mosquitoes
before the viruses are transmitted to humans.
Mosquitoes are routinely collected in Brazoria,
Cameron, Dallas, El Paso, Galveston, Harris,
Hidalgo, Jefferson, Lubbock, and Nueces Coun-
ties. Collection of mosquitoes also takes place
Figure 1. Endemic Arboviral Activity:
By Region, 1996 Summary
PHR
2
3
4
5
6
7
8
9
10
11
NONE
SLE, WEE
N/A
NONE
N/A
NONE
SLE
N/A
N/A
N/A
NONE
CE, WEE
N/A
WEE
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
SLE
CE
PHR = Public Health Region; CE = California Encephalitis;
SLE = St. Louis Encephalitis; WEE Western Equine Encephalitis
NONE = No activity detected through routine surveillance
N/A = No surveillance activites conducted
23 4
75
Public
Health 1
Regions
in other counties as conditions warrant.
Additionally, sentinel flocks of chickens are
maintained in the Lubbock and the Dallas/Ft.
Worth areas. TDH also monitors arboviral infec-
tions in animal species that the Texas Veterinary
Medical Diagnostic Laboratory discovers during
routine screening.
The number of cases of SLE, the most com-
mon arboviral disease reported in Texas, var-
ies greatly from year to year. For the past 10
years, the annual number of reported SLE
cases ranged from 0 to 42. In 1996 only 2
cases of SLE and 1 case of CE were reported.
There were no deaths. The most recent out-
break of dengue fever, which occurs occa-
sionally in Texas, was in 1995. There were 29
dengue cases (7 endemic) associated with
this outbreak.
Last summer, DPN began publishing a chart
summarizing endemic arboviral activity for
the previous year. Figure 1 provides a sum-
mary of arboviral activity by region for 1996;
Figure 2 illustrates the most current data for
calendar year 1997. A TDH Internet web
page for up-to-date data on arboviral activity
in Texas is currently under construction. Ac-
cess instructions will be published in DPN as
soon as this web site is completed.
For further information contact Jeff Taylor or
Julie Rawlings of the TDH Infectious Disease
Epidemiology and Surveillance Division at
(512) 458-7676.
Continued v
DPN
Page 3
