Planning for rift valley fever: Use of GIS to estimate the human health threat of white-tailed deer (Odocoileus virginianus)-related arbovirus transmission in an urban-suburban environment in Northeast, Ohio, USA

In bioterrorism, the introduction and accelerated spread of highly pathogenic viruses in naïve populations could incapacitate or kill large numbers of susceptible animals and people. This paper discusses the zoonotic and vector abundance factors likely to be involved in determining the areas of highest risk for an outbreak of an exotic pathogen, Rift Valley Fever Virus (RVFV) within Cuyahoga County, located in the northeastern part of the state of Ohio, USA. Our objective is to begin the formulation of likely threats, and to map out areas for initial prioritization for public health interventions that will most effectively restrict transmission of RVFV. Analyses were performed using ArcGIS version 9.2. Based on the features of zoonotic spread likely to occur in the local environment, we examined ecological variables that included 1) measured density of June/July or August/September Culex and Aedes vexans mosquito species; 2) measured density of human population; and 3) projected pre and post-culling density estimates for White-tailed deer. For each variable, density raster maps were created and density values were divided into ten equal intervals. Raster calculator was used to evaluate all three raster density maps simultaneously. A risk threshold was set above the fourth decile for all variables to evaluate their spatial intersection. Preliminary results suggest that geographic overlap of mosquitoes, humans, and deer occurs in the periphery of Cleveland proper for the June/July period. This region appears to extend into contiguous municipalities for the August/September period. It is expected that health planners can use such pre-formulated “temporal risk maps” to identify when and where control measures should be targeted spatially to reduce transmission in the event of an outbreak.