Natural infections of giant liver flukes (Fascioloides magna) occur primarily in cervids and bovids. In northeastern North America, a common definitive host for giant liver flukes is the white-tailed deer (Odocoileus virginianus). Giant liver flukes cannot reproduce in moose (Alces alces) and eventually die, but only after causing extensive tissue damage in the liver. We used data on the occurrence of giant liver flukes in adult moose collected between 1972 and 2000 from northeastern Minnesota, USA. These data were recorded by 93 km2 sampling units (square grid of 9.66 km on each side). Sample sizes varied between 0 and 45 adult moose examined per sampling unit. We fitted a second-order global polynomial model to adjust for trends in the occurrence of flukes across the study area, modeled the de-trended data using a circular semi-variogram model, and finally kriged our data, arriving at a predicted response surface for the occurrence of liver flukes in moose. Correlational analyses indicated that the occurrence of liver flukes in moose was influenced more by the density of white-tailed deer based on rates of hunter harvest (r = 0.54) than was the proportion of wetland habitats (r = 0.25). Ordinary least-squares multiple regression (R adj = 0.29, AICc = 795.3) documented a strong relationship between the occurrence of liver flukes in moose and population density of white-tailed deer (p < 0.001) but a weaker relationship for wetland habitats (p = 0.16). A geographically weighted multiple regression produced a stronger relationship (R adj = 0.60, AICc = 765.7). Disease maps, as we developed here, are a useful geospatial tool that has relevance for understanding disease processes in moose that may be extended to other mammals.
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