The effect of non-reservoir host species, which occur intermittently over time, on pathogen prevalence among a reservoir species is poorly understood. We investigated whether voles, Microtus spp., which occur intermittently, influenced infection prevalence of Sin Nombre hantavirus (SNV, Bunyaviridae: Hantavirus) in deer mice, Peromyscus maniculatus, whose populations are persistent. We considered whether infection prevalence among deer mice was proportional or independent of vole density (density-dependent or density-independent respectively). We used 14 years of data from central Montana to investigate this relationship. We considered a number of possible caveats which could influence interpretation of a relationship between voles and infection prevalence among deer mice: delayed-density-dependent transmission within deer mice, seasonal fluctuations in vole and deer mouse abundance and deer mouse infection prevalence, correlations between vole and deer mouse populations, and density-dependent transmission within deer mice.

Results/Conclusions

By partitioning deer mouse abundance into low, medium and high abundance categories and analyzing density-dependent and density-independent relationships between voles and infection prevalence of deer mice within these categories, we overcame these possible caveats in the low and medium deer mouse abundance categories. There were significant reductions (47-90%) in hantavirus infection prevalence among deer mice when voles were present at the lowest deer mouse abundance category. This relationship was independent of vole density. A number of studies have documented that spatial variability in host diversity is associated with reductions in pathogen prevalence by a hypothesized “dilution effect”. We suggest a “dilution effect” may also occur where host diversity fluctuates temporally. Preservation of host species diversity and optimization of environmental conditions which promote occurrence of ephemeral species, such as voles, may result in a decrease in infection prevalence of a hantavirus in reservoir hosts. Our results may extend to other zoonotic infectious diseases.