Abstract
The presence of many pathogens varies in a predictable manner with latitude, with infections decreasing from the equator towards the poles. We investigated the geographic trends of pathogens infecting a widely distributed carnivore: the gray wolf (Canis lupus). Specifically, we investigated which variables best explain and predict geographic trends in seroprevalence across North American wolf populations and the implications of the underlying mechanisms. We compiled a large serological dataset of nearly 2000 wolves from 17 study areas, spanning 80° longitude and 50° latitude. Generalized linear mixed models were constructed to predict the probability of seropositivity of four important pathogens: canine adenovirus, herpesvirus, parvovirus, and distemper virus—and two parasites: Neospora caninum and Toxoplasma gondii. Canine adenovirus and herpesvirus were the most widely distributed pathogens, whereas N. caninum was relatively uncommon. Canine parvovirus and distemper had high annual variation, with western populations experiencing more frequent outbreaks than eastern populations. Seroprevalence of all infections increased as wolves aged, and denser wolf populations had a greater risk of exposure. Probability of exposure was positively correlated with human density, suggesting that dogs and synanthropic animals may be important pathogen reservoirs. Pathogen exposure did not appear to follow a latitudinal gradient, with the exception of N. caninum. Instead, clustered study areas were more similar: wolves from the Great Lakes region had lower odds of exposure to the viruses, but higher odds of exposure to N. caninum and T. gondii; the opposite was true for wolves from the central Rocky Mountains. Overall, mechanistic predictors were more informative of seroprevalence trends than latitude and longitude. Individual host characteristics as well as inherent features of ecosystems determined pathogen exposure risk on a large scale. This work emphasizes the importance of biogeographic wildlife surveillance, and we expound upon avenues of future research of cross-species transmission, spillover, and spatial variation in pathogen infection.
Highlights
The presence of many pathogens varies in a predictable manner with latitude, with infections decreasing from the equator towards the poles
We considered a range of area sizes and selected a 200-km radius because human density and habitat quality were less variable in comparison with small or large radii, and it is more congruent with wolf dispersal distance[49,50]
Most study areas were sampled for 10 years and, on average, 12 wolves were sampled per year
Summary
The presence of many pathogens varies in a predictable manner with latitude, with infections decreasing from the equator towards the poles. Seroprevalence of all infections increased as wolves aged, and denser wolf populations had a greater risk of exposure. We assess how well geography alone can explain the observed variation in seroprevalence, and contrast this with variables that may confer a mechanistic understanding of pathogen exposure at individual and population levels, such as wolf and human densities, wolf age, sex, coat color, pack size, or habitat quality (Table 2). To investigate the drivers of pathogen exposure, we compiled a serological dataset of North American wolves spanning 17 study areas across 80° of longitude, from the Alaska Peninsula in the west to Ontario in the east, and 50° of latitude, from Ellesmere Island in the north to Arizona and New Mexico in the south (Fig. 1). Wolf sera were tested for antibodies to four viruses: canine adenovirus-1 (i.e., adenovirus), canine parvovirus-2 (i.e., parvovirus), canine distemper virus (i.e., distemper), canine herpesvirus (i.e., herpesvirus), and two protozoa: Neospora caninum, and Toxoplasma gondii (Table 1)
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