Mosquito Surveillance for West Nile Virus

State: TX Type: Model Practice Year: 2004

West Nile virus (WNV) arrived in North Texas in 2002. From a public, media, and professional perspective, many questions needed to be answered. One question was the overall prevalence of WNV in local mosquitoes. To address this and other vector-related issues, a cooperative countywide mosquito surveillance project was proposed for 2003. Local governments would collect pools of mosquitoes for testing and bring them to the Tarrant County Public Health Department (TCPHD) laboratory and environment health divisions for analysis. Instead of shipping mosquito samples 200 miles, they would be tested at the TCPHD. Instead of using traditional testing methods, DNA analysis (RT-PCR) would be used. Reporting time would be reduced from two-to-three weeks to two-to-four days. Detections of WNV would immediately be reported to the participating city, which would determine an appropriate response (mosquito bite prevention and/or mosquito control). A response guide was prepared to assist participants.
In view of the rapid spread of WNV throughout Texas during 2002, it was clear that additional data and actions by local governments were needed in order to appropriately address WNV concerns in the community. Local governments responded by taking actions to control mosquitoes and/or conducting educational efforts on avoid being bitten and reducing residential mosquito breeding sites. Prior to 2002, there was no designated vector control staff at the TCPHD. To create a mosquito monitoring and response program in association with local governments, the TCPHD: Identified an experienced existing staff person to lead the project.  Purchased and supplied all local governments with mosquito monitoring equipment.  Trained all participating local governments. TCPHD used innovative technology to test mosquitoes. The department developed a WNV response guide for all participants. TCPHD staff notified local and state government when WNV was detected. Local governments were responsible for collecting mosquitoes and responding to lab results. Cross-utilization of lab equipment that is maintained for bioterrorism responses allows the TCPHD to rapidly identify the presence or absence of West Nile Virus in mosquito samples. In 2003 no other health department in Texas was using DNA analysis technology for mosquito testing. The use of this technology speeds up processing time, compared to traditional lab testing (cell cultures and IFA methods), and also permits staff to run tests on-site at the local health department, as opposed to shipping mosquitoes 200 miles to the State lab for testing. Accuracy and sensitivity are also increased. DNA analyses are performed using RT-PCR (Real Time Polymerase Chain Reaction) technology. All participants received weekly updates, with e-mailed GIS maps showing their own and other participants’ sampling sites, locations of WNV positive mosquitoes, horse cases, and cities with human cases.
Agency Community RolesThe TCPHD was the lead agency in developing and implementing the countywide Mosquito Surveillance for WNV Program. The primary stakeholders are the 29 participating local governments in Tarrant County. They are essential to the operation of the program. A close planning and implementation partnership was required in order to determine, for example, the amount of work that each of the partners could perform; who was to be contacted within each local government; and how to rapidly communicate with each designated person(s) regarding mosquito collection scheduling, equipment problems, and WNV positive and negative test results. Collaboration is part of the program. This surveillance project requires at least weekly communication with stakeholders via e-mails, phone calls and personal visits when mosquito collections are delivered to the TCPHD. Texas is fairly unique in that it grants cities the authority to make their laws, but counties are restricted to enforcing laws delegated to them by the State. The result is that cities and counties in Texas are not typically integral partners in programs. In the Tarrant County mosquito-monitoring program, all participating local governments are integral partners. Costs and ExpendituresCosts include staffing of at least one full-time equivalent position ($35,000), collection and surveillance ($15,000), and laboratory supplies for light cycler including probes for WNV and SLE ($3,500). TCPHD already had a light cycler. If a light cycler has to be purchased, anticipate spending an additional $60,000. The initial equipment/materials purchase of $15,000 was funded through a grant from CDC/Texas Department of Health. Light cycler/supplies were also supported by grant funding. Staffing was funded through general funds. On-going funding of the program is through local support by the TCPHD. As the program continues, some fees may be required. Fees would be required for any participants located outside of Tarrant County. ImplementationObjective: Create a countywide WNV Mosquito Surveillance ProgramTask 1.1 – Identify essential components and activities, including laboratory services.Task 1.2 – Enlist agency and local government participants.Task 1.3 – Obtain equipment.Task 1.4 – Train all participants on equipment use, safety, and data entry.Task 1.5 – Schedule mosquito collections and lab service from mid-May through September. Objective: Share lab test results, emerging data and GIS maps with all participants.Task 2.1 – Establish a communication network with primary and secondary contact.Objective: Support local government WNV response optionsTask 3.1 – Prepare a guide to be used by participants to individualize their responsesTask 3.2 – Act as an advisor to any participant.  
Process Evaluation: Personal communication with local governments confirms that the implementation strategy was effective. The final proof is that program operated, as planned, with minimal refinements. From a workload/workflow perspective, while WNV detections were peaking, processing times slowed by several days. This was due to the need to re-test positive samples to confirm WNV detections. Re-testing was performed to duplicate CDC’s criteria for RT-PCR testing. From a communication perspective, switching to weekly email updates of all participants with GIS maps, data and comments was very effective, but required additional staff time to accomplish. Outcome Evaluation:The program’s outcome is evaluated using three criteria: The majority of local governments in the county participate in collecting mosquitoes. During 2003, 71% of local governments in Tarrant County collected mosquitoes. The 2003 mosquito season produced useful information, which was obtained by entering data from collection reports into a Microsoft Access™ database. The data was then analyzed using SPSS™ statistical analysis software. Not only did staff obtain useful information for the 2003 program, a baseline of WNV information was established that will allow valid comparisons on the status of WNV vectors over time. During 2003 designated representatives were notified regarding 127 positive mosquito pools. Local governments were to be notified within a day after WNV was reported in mosquito pools. Each local government then determined the appropriate action to be taken for their community. An unplanned result is the relationship with a variety of operational and administrative level staff. Another consequence was that a biological field sampling program was established that could be modified and used for other purposes, should an emergency need arise. A third consequence was the preparation of a guidance document that would assist local governments in responding to positive WNV mosquito notifications by utilizing health department staff, code compliance officers or others likely to be present in most community governments.
SustainabilityAfter 2003, Tarrant County Commissioners approved a new permanent full-time position to sustain the program. This assures that Tarrant County will continue cooperation and sharing of work, data, and information with participating local governments. Local governments have also indicated they will continue to participate in 2004. Two cities that did not participate last year are interested in joining for 2004. Several local governments outside of Tarrant County have also asked to join the surveillance program. These additional stakeholders could be added if current stakeholder numbers drop. PowerPoint™ presentations about the program will continue to be given to audiences via state and local conferences. Starting in 2004, Dallas and Collin Counties will initiate countywide WNV mosquito surveillance programs similar to Tarrant County's. Lessons LearnedEach procedure and task involved a significant amount of two-way communication.. The newness of the West Nile virus combined with the professional and public pressure to better understand what was happening in the community added to the need to effectively communicate with all participants. An important lesson is to appoint an experienced, operationally oriented person to develop procedures and tasks and to work directly with local governments. This position will be working with both professional and non-professional staff to implement and maintain the program.