For the County of Mercer, New Jersey, Mosquito-Borne Diseases Pose a Serious Challenge
Combating the Asian Tiger Mosquito
By Matthew Kabak, Eric Williges, Isik Unlu, Matthew Lawson, and Ary Farajollahi, County of Mercer, New Jersey
The County of Mercer, New Jersey, lies equidistant between New York City, New York, and Philadelphia, Pennsylvania. Its geography ranges from Appalachian piedmont forests to farms on the coastal plain. It hosts extensive freshwater and tidal marshes, the state's urban capital of Trenton, and a booming interstate "edge city" near Princeton University. Such diversity provides an ideal location to study mosquitoes and arthropod-borne diseases (arboviruses).
Mercer County Mosquito Control (MCMC) monitors, inspects, and manages all mosquito-related activities within the county. Its two main responsibilities are to monitor and control nuisance mosquito populations and to protect the safety of the general public from mosquito-borne diseases, such as West Nile virus and eastern equine encephalitis. MCMC uses integrated pest management techniques, along with continual surveillance of local mosquito populations and responses to service requests generated by local residents, to keep mosquitoes at tolerable levels.
In recent years, populations of an invasive mosquito species, Aedes albopictus, the Asian tiger mosquito, have been increasing dramatically. This species poses a serious challenge because of its daytime biting habits, ubiquitous larval habitats, and danger as a disease vector. In fact, six arboviruses (eastern equine encephalitis, West Nile, Keystone, Tensaw, Cache Valley, and Potosi) have been isolated from this species since its introduction into the United States. Additionally, this mosquito is an efficient vector of other nonendemic arboviruses such as dengue, yellow fever, and chikungunya. With globalization and modern travel patterns, it may be only a matter of time before an infected traveler imports one of these exotic diseases.
From a management perspective, MCMC has a great deal of spatial information to track, including larvicide applications for regulatory compliance, lab test results from trapped mosquitoes, and animal and human disease incidence for epidemiological purposes. For this reason, MCMC was one of Mercer County's early adopters of GIS to help manage data. MCMC currently uses ArcGIS Desktop software and ArcSDE 9.2 with Microsoft SQL Server 2005 to develop policy and daily inspection routines and manage most data.
Ron Oppenheimer, a mosquito inspector, states, "GIS not only provides me with an accurate visual depiction of where mosquito habitat is located, it also allows me to visualize where other hidden potential habitats may lie."
The countywide GIS consists of an enterprise geodatabase managed with ArcGIS Server Advanced Enterprise and hosted at the county administration building in Trenton. From offices seven miles away, MCMC accesses hydrologic, topographic, transportation, and demographic feature classes in the enterprise geodatabase by consuming server-cached map services. In addition, MCMC also uses local personal geodatabases, managed with ArcGIS Desktop applications, to maintain spatial data specific to mosquito control issues, including, most recently, data for a consortium research project on the surveillance and management of the invasive Asian tiger mosquito. This local data addresses a wide variety of needs, from tracking pesticide usage by each inspector across the course of a season to creating specific maps in response to a resident complaint or question.
MCMC also uses other GIS-related tools. One is an industry-specific vector management system with integrated GIS capabilities for mosquito and vector control programs. The system allows managers to efficiently organize, host, and report mosquito data, which can be exported in a shapefile format and added as a layer in the ArcGIS Desktop ArcMap application. Another tool is the Pictometry image viewer extension to ArcMap from Esri Business Partner Pictometry International Corp. (Rochester, New York). With oblique and orthogonal aerial image libraries from 2005, 2007, and 2009, MCMC staff can view high-resolution imagery (6 inches per pixel) from several angles and several points in time. The approximate 40-degree angle of the oblique imagery and leaf-off flight schedule provides them with greater detail than common orthogonal images. By analyzing these images and comparing them with field comments from inspectors, it is possible to narrow down the reason for a local service request before sending any inspectors to the field.
MCMC's team of inspectors provides surveillance and control of local mosquito populations across Mercer County. In the field, team members use Trimble GeoXT GPS units and Pathfinder software from Esri Business Partner Trimble Navigation Limited to track trapping and treatments at active mosquito sites and record work in response to residents' service requests. GPS data points are imported into ArcGIS feature classes and activated on top of vector and raster layers. This gives supervisors a visual way to identify hot spots around the county in which a cluster of data points could correspond to high mosquito populations or disease activity. Mosquitoes are collected with a variety of vector surveillance traps and tested in the laboratory to determine the presence and prevalence of diseases such as West Nile virus and eastern equine encephalitis. After test results are imported into ArcGIS, supervisors can visualize virus activity and deploy inspectors to control adult mosquito populations in a precise and targeted manner. Maps of disease incidence and pesticide applications are used to compare current activity to historic activity and ensure that MCMC serves the county as efficiently as possible.
MCMC's study and control of Aedes albopictus offers a valuable example of GIS/GPS technologies at work. Introduced into the United States in 1985, the species now infests 30 states and continues to expand its range. The species was first detected in New Jersey in 1995, and its range has expanded to all but the far northwest corner of the state. Public health officials concerned with arboviruses recognize this species as a potential vector of debilitating epidemics, but it is also regarded as one of the most significant nuisance mosquitoes across its range. Ae. albopictus is an aggressive and persistent human-biting species that, in contrast to most mosquitoes, feeds during the day and can significantly impact human environmental quality. This mosquito thrives in artificial containers, even bottle caps, particularly in urban areas, and has been responsible for most of the service requests from Mercer County residents in recent years. Standard approaches to mosquito abatement fail to control this species, due to its unique behaviors. For an urban pest such as Ae. albopictus, an area-wide approach for control is imperative, since populations are diffuse and the potential for dispersal to neighboring properties is high.
To combat the Ae. albopictus infestation and develop best practice interventions, MCMC is participating in a multidisciplinary research study that incorporates demographic and land-use analysis, extensive public education and involvement, and focused application of established biological and chemical control interventions.
The Asian tiger mosquito study uses advanced geoprocessing and geostatistical tools in ArcGIS. Using data from enterprise and personal geodatabases, the research team selected three experimental areas in the city of Trenton similar in census block size, tax parcel size, economic factors, and population density of Asian tiger mosquitoes. Team members selected, clipped, and merged study areas using parcel and street centerline layers. Census blocks clipped to the study areas were enumerated and stratified into site locations. At the end of the mosquito season, surveillance, treatment, and service call data for each risk unit can be laid over various hydrologic, demographic, and topographic feature classes to allow visual and statistical study of outcomes. Analysis will use ArcGIS and other applications to predict and model prime Ae. albopictus habitats. This will permit rapid deployment of mosquito inspectors.
About the Authors
Matthew Kabak is a GIS specialist for Mercer County, Eric Williges is a wetlands specialist for MCMC, Isik Unlu is an entomologist for MCMC, Matthew Lawson is a principal planner for Mercer County, and Ary Farajollahi is the superintendent for MCMC.