Texas Department of State Health Services - Arbovirus Surveillance Program

- Arbovirus Surveillance Program \| Arbovirus Resources \| Entomology Resources - - Arbovirus Home -
What We Do
The Arbovirus Surveillance Program at the Texas Department of State Health Services (DSHS) identifies mosquitoes and detects and tracks the circulation of encephalitis viruses in mosquitoes in the environment prior to the development of human disease.
Program Components:	Zoonosis Control Branch Health Service Regions (HSR) Infectious Disease Control Unit Laboratory Arbovirus/Entomology Team

Targets & Testing
The Program targets mosquito species known to be primary vectors of encephalitis viruses recognized in Texas and that produce disease in humans. Based on past experiences with mosquito-borne encephalitis in Texas, Culex quinquefasciatus and Culex tarsalis are the important vectors for West Nile, St. Louis encephalitis, and western equine encephalitis viruses. Culiseta melanura is the known enzootic vector of eastern equine encephalitis virus (EEE); however, Aedes, Coquillettidia, Anopheles, and Culex species may be bridge vectors and transmit EEE virus to both humans and horses. The tree-hole mosquito Ae. triseriatus is the primary vector for La Crosse virus. In 2002, West Nile virus (WN) was first detected in wild birds collected in Houston, Texas. WN virus has been isolated from Cx. quinquefasciatus, Cx. salinarius, Cx. (Melanoconion) sp, Cx. restuans, Cx. tarsalis, Cx. nigripalpus, Ae. albopictus, Ae. taeniorhynchus, and Ps. columbiae. Mosquito specimens are submitted to the DSHS from numerous Texas city and county health departments, health service regions, military installations, universities, and local mosquito control programs. Specific information on field surveillance techniques is available at this site. At the Laboratory, the mosquitoes are identified to species, pooled, and tested for the presence of arboviruses. Whenever the laboratory isolates one of these viruses, laboratory personnel notify the agency that submitted the specimens and the appropriate HSR, as well as the Zoonosis Control Branch. The responsible HSR will work with the submitting agency to help assess any health threats and determine what mosquito control measures need to be initiated based on the virus detected.

Program Summary
Routine arboviral isolation studies (from mosquitoes collected around the state) are conducted from May through November of each year. The period may be extended in the event of an outbreak of encephalitis. Mosquitoes received at other times of the year are identified to species only. Such specimens may be submitted for determination of species distribution and density, seasonal activity, and effectiveness of local control programs on mosquito populations. Arboviral isolation studies are not conducted on nestling pigeons or other birds. Isolation studies from vector mosquitoes provide more useful information. However, special surveillance proposals with prior approval will be considered. Mosquitoes received in unsatisfactory condition will be identified to species only. Vector mosquito species will be pooled except following the isolation of a pathogenic arbovirus. Subsequent species of mosquitoes collected in that county will be kept separate. Negative isolation results for mosquito pools consisting of pest species are not very meaningful. Therefore, arboviral isolation studies on species that are not implicated in the transmission of these viruses will be limited. The gravid trap and use of aspirators at natural resting sites are the preferred methods of collecting adult mosquitoes. New program participants should contact the Arbovirus/Entomology Team for the appropriate training at least one month in advance. Sentinel chickens are no longer tested for arboviral antibodies. Any proposed changes to standard field activities must be coordinated with the Arbovirus/Entomology Team.

Public Health Benefits
The Program:
Serves as an early warning system to detect the presence of virus activity in mosquito populations before humans are infected (Note: The prevention of human cases is preferable to treatment after infection because there is no specific anti-arboviral therapy available and no vaccine readily available to the general public.) Informs local health officials and physicians of the potential for human infections Informs state and local mosquito control programs of both vectors and viruses present in their areas so that control measures can be initiated quickly and appropriately Provides information to the general public of arboviral activity so that they can take proper precautions to avoid contact with mosquitoes Provides an opportunity to prevent potential epidemics Has the ability to detect the introduction of new arboviruses of public health significance, for example the West Nile virus in 1999.