The Arbovirus Surveillance Program at the Texas Department of State Health Services is designed to monitor mosquitoes to detect and track the circulation of encephalitis viruses in mosquitoes in the environment prior to the development of human disease due to these viruses. This is a cooperative program including the Zoonosis Control Group , General Sanitation, and Infectious Disease Control Unit of TDSHS, as well as the Arboviral Disease Team of the laboratory.

The program targets mosquito species known to be primary vectors of encephalitis viruses recognized in Texas that produce disease in humans. Based on past experiences with mosquito-borne encephalitis in Texas, Culex quinquefasciatus and Culex tarsalis are the primary vectors for St. Louis encephalitis and western equine encephalitis virus respectively. Culiseta melanura is the known enzootic vector of eastern equine encephalitis virus. However, Aedes, Ochlerotatus, Coquillettidia, Anopheles, and Culex species may be bridge vectors and transmit EEE virus to both humans and horses. The tree-hole mosquito Oc. triseriatus is the primary vector for La Crosse (LAC) virus. In 2002, West Nile virus (WNV) was first detected in wild birds collected in Houston, Texas. WNV has been isolated from Cx. quinquefasciatus, Cx. salinarius, Cx. (Melanoconion) sp, Cx. restuans, Cx. tarsalis, Ae. albopictus, and Ps. columbiae.

Mosquito specimens are submitted to the Texas Department of State Health Services from numerous Texas city and county health departments, public health regions, military installations, universities, and local mosquito control programs. Specific information on field surveillance techniques is available at this site. These mosquitos 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 Zoonosis Control, General Sanitation, and Infectious Disease Epidemiology and Surveillance Divisions of TDSHS. These Divisions of TDSHS 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.

Summary of the TDSHS Arboviral Surveillance Program

Routine arboviral isolation studies from mosquitoes collected around the state will be conducted from May through October of each year. The period may be extended in the event of an outbreak of encephalitis.
Mosquitoes received at other times of the year will be identified only. Such specimens may be submitted for species distribution and density, seasonal activity, and effect 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.Special surveillance proposals with prior approval will be considered.
Mosquitoes received unsatisfactory will be identified 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 using aspirators at natural resting sites are the preferred methods of collecting adult mosquitoes.
New program participants should contact the Laboratory Services Section 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 Laboratory Services Section.

Importance of the Arbovirus Surveillance Program to Public Health

The activities of the Arbovirus Surveillance Program provide many public health benefits including:

The program serves as an early warning system to detect the presence of virus activity in mosquito populations before humans are infected.
The program informs local health officials and physicians of the potential for human infections.
The program 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.
The program provides information to the general public of arboviral activity so that they can take proper precautions to avoid contact with mosquitoes.
Surveillance provides an opportunity to prevent potential epidemics.
Prevention of human cases is preferable to treatment after infection since there is no specific anti-arboviral therapy available and no vaccine readily available to the general public.

Last Updated March 17, 2006