BACKGROUND: In response to the Zika outbreak in the Americas, we substantially increased our mosquito monitoring activities throughout Washington, D.C. Facilitating a place-based characterization of the urban environment where disease carrying vectors live and breed, the D.C. Department of Health (DOH) turned to technology to improve how we target at-risk populations. GIS concepts that possess capabilities which written narratives cannot provide were used to inform the location, spatial relationships, and, environmental/social issues associated with areas potentially harboring virus carrying vectors.
METHODS: Using ArcGIS online and ArcMap 10.4 to map equidistant trap sites ensured coverage throughout the city and mapped weekly larvicidal treatments to catch basins targeting mosquito larvae. These maps gauged weekly coverage by ward, ensuring a 30-day cycle application, coinciding with product efficacy. Surveillance was conducted with a minimum 4 traps per ward from April-October 2016, following a 48-hour trap-to-harvest protocol utilizing both gravid and carbon dioxide traps, speciating all harvested mosquitoes weekly at the Public Health Lab.
RESULTS: After trapping, harvesting, sorting and testing 1282 pools (15,121 specimens) for Zika, WNV, Dengue, and Chikungunya viruses, no mosquitoes were found to be carrying Zika. Approximately 53.5% of our sites (15 of 28) tested positive for WNV. Breakdown of the specimens collected were as follows: 12,821 (85%) Culex Pipiens, 47 (0.3%) Culex Restuan, and 380 (2.5%) Aedes japonicus. Included were species with the potential to transmit Zika virus: 1125 (7.4%) Aedes albopictus, 187 (1.2%) Aedes aegypti, and, 561 (3.7%) Aedes Species (unknown). A 30-week sampling produced WNV positive pools 46% of the time. Larviciding goals were deficient mainly due to lack of resources.
CONCLUSIONS: Mapping of the 2016 arbovirus data identified gaps in spatial distance between the historical trap sites and vulnerable populations, allowing us to establish better site locations in terms of coverage/ward and habitats with known concentrations of Aedes species. Analysis of the trap sites using GIS identified infrastructure where new sites will be located in 2017, targeting the most vulnerable populations (pregnant women and women of child bearing age) within range of likely concentrations of potential Zika vectors. Mapping WNV Hot-Spots helped inform trapping protocols regarding potential local Zika transmission due to the confirmed the presence of the Zika vector in D.C. Dedicated personnel will be utilized to larvicide in 2017. Findings further indicated the need to focus on proximity to OB/Gyn facilities and other healthcare facilities related to protecting pregnant women from this public health threat.