West Nile virus (WNV), an invasive arbovirus, spread rapidly throughout North America following its introduction to New York City in 1999. Pathogen amplification cannot be observed directly but must be monitored through its impact on avian hosts, or incidental infections in humans and domestic animals. Exposure to WNV results in high levels of mortality for many species of birds in laboratory challenge studies, though evaluating population-level impacts in the wild is difficult. Biologists have long struggled with estimating wildlife populations and monitoring changes in abundance because collecting data across space and time is expensive and data quality inherently depends on observer proficiency. However, Bayesian hierarchical modeling can accommodate these sources of variability, and where WNV-related mortality is significant, avian population change may provide a spatio-temporal proxy for pathogen amplification. Initial efforts have demonstrated significant declines in some species following WNV emergence across North American (LaDeau et al. 2007). Calder and LaDeau are now developing hierarchical statistical models that capture the spatial and temporal dependence structure of this pathogen amplification using annual measures of local American crow populations from across North America.

References:
LaDeau, S. L., Kilpatrick, A. M., and Marra, P. P. (2007). West Nile virus emergence and large-scale declines of North American bird populations. Nature, 447, 710-713.

• Cary Institute of Ecosystem Studies