Environmental fluctuations lead to predictability in Sin Nombre hantavirus outbreaks

Predicting outbreaks of zoonotic infections in reservoir hosts that live in highly fluctuating environments, such as Sin Nombre virus (SNV) in deer mice, is particularly challenging because host populations vary widely in response to environmental conditions and the relationship between field infection rates and abundance often appears to contradict conventional theory. Using a stage-structured host-pathogen model parameterized and crossvalidated from a unique 15-year data set, we show how stochastic population fluctuations can lead to predictable dynamics of SNV in deer mice. Significant variation in host abundance and the basic reproductive number of the virus results in intermittent crossing of the critical host population density necessary for SNV endemicity and frequent local extinctions. When environmental conditions favor growth of the host population above the threshold, host- pathogen interactions lead to delayed density dependence in reservoir prevalence. The resultant ecological delay may provide a neglected opportunity for outbreak prediction in zoonoses.