Epidemiology of suburban deer

Urban and suburban development has expanded beyond the traditional core of major cities. Preservation of open spaces in metropolitan landscapes provides aesthetic and recreational values for humans. However, white-tailed deer ( Odocoileus virginianus) populations in North America are overabundant in many suburban areas. This trend is directly related to changes to habitat as a result of landscape alteration and fragmentation caused by humans. This close relationship between humans and wildlife increases the risk for zoonotic disease transmission from many vectors, such as mosquitoes and ticks. There is limited research for suburban deer examining the relationship between zoonotic prevalence and ecological factors, such as habitat. Additionally, an extensive search of deer ecology and wildlife disease literature revealed no peer-reviewed publications of zoonoses from suburban white-tailed deer. From 1995--99, I conducted a zoonotic serological survey of live-captured (tagged and radio-collared) and culled deer from Chicago, Illinois forest preserves for Jamestown Canyon (JC) and LaCrosse (LAC) encephalitis viruses, toxoplasmosis, and leptospirosis. The prevalence of sera samples collected from suburban white-tailed deer (live-captured and culled) was 55.9% for Toxoplasma gondii (n=443), 16.2% for Leptospira spp. (n=444), 38.1% for JC virus (n=404), and 6.7% for LAC virus (n=404). Prevalence was higher for adult deer for all pathogens sampled except Leptospira spp. Prevalence also was less likely in males for JC virus. A higher prevalence for T. gondii and JC virus was detected at Des Plaines (DP) and prevalence for Leptospira spp. was less likely at DP. Differences in year the sample was collected were present for T. gondii, Leptospira spp., and JC virus. Variation in month the samples were collected was evident for T. gondii, Leptospira spp., and LAC virus. Main effects variables (age, sex, site, year, and month) for multivariate logistic regression (LR) models were screened using backward stepwise elimination (p≤0.20). The final LR model for T. gondii contained all main effects variables. Leptospira spp. and JC viral models both contained age, site, and year, while the final LAC viral LR model contained age, sex, and month. A subsample of deer (n=169 from DP and Palos; radio-collared and culled) analyzed for JC and LAC viral antibodies was used to evaluate habitat characteristics. Radio-collared does selected for forest, savanna, and grassland habitats (available habitat=p<0.0001; home range=p<0.001). Akaike's Information Criterion (AICc) optimal models for JC contained water and wetland habitat parameters while LAC models contained forested habitat. Deer biological parameters for JC viral models included age and month/year the samples were collected. Total home-range or buffer size and month were biological parameters contained in LAC viral models. Blood samples from live-captured and culled deer tested for JC (238 seropositive and 402 seronegative cases) and LAC viruses (51 seropositive and 402 seronegative cases) from 11 forest preserves were used for spatial analysis. Using the Bernoulli model in the space-time scan statistic in SaTScanRTM, a significant viral "hot spot" was revealed for JC virus in DP (p=0.009). A significant cluster for LAC virus was also found in DP (p=0.005). All clusters were independent of each other. Temporal patterns for JC virus spanned samples from December 1, 1995 to March 31, 1998. This research demonstrates deer are positive for several zoonotic diseases in the Chicago area. The environmental and habitat factors required to maintain pathogens and vectors are present at various levels in Cook County Forest Preserves. "Hot spots" are present for JC and LAC viruses and deer serve as an effective wildlife sentinel. The relationship between habitat and spatial data can be used to focus surveillance. This research not only quantifies deer exposures to pathogens, but also provides a more sensitive assessment of risk than human or pet surveillance alone. Wildlife species, such as deer, serve as effective disease sentinels because they are exposed to potential pathogens everyday in their natural environment when humans and pets are typically random and accidental exposures. Wildlife ecologists have a responsibility to increase public knowledge about the health status of animal populations while protecting humans and domestic animals from zoonotic diseases. This research represents the largest suburban deer zoonotic surveillance project to date in the United States and provides evidence that suburban deer are effective biomonitors for zoonoses. International, federal, and state management agencies collect various harvested wildlife species annually which could be easily accessed for zoonoses sampling. Annual culling of deer continues in Chicago area forest preserves and samples should be collected and analyzed for zoonotic diseases with minimum effort and cost. Results should be communicated to public health officials to assist in focusing vector control and to notify the public of potential exposures.