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.
Bibliographical noteFunding Information:
We thank the wildlife professionals that contributed wolf sera, serology data, and metadata to this project: Erin Stahler, L. David Mech, Dean Beyer, Erin Largent, Susan Dicks, John Oakleaf, the Mexican Wolf Project, Lindsey Dreese, Brent Patterson, Emily Almberg, Montana Fish Wildlife and Parks, Heather Fenton, Shari Willmott, and the countless unlisted biologists that collected these samples and data through the decades. Financial support includes: E.E.B. and P.J.H. endowment from Verne Willaman; E.E.B. and P.C.C. U.S. Geological Survey (Grant G17AC00427); D.W.S., D.R.S., and D.R.M. NSF LTREB grant DEB–1245373 and many donors to Yellowstone Forever, especially Annie and Bob Graham and Valerie Gates; M.H. Parks Canada and NSF LTREB award 1556248; G.R. Pittman-Robertson Federal Aid in Wildlife Restoration Program and the State of Alaska general funds; K.B. Federal Aid in Support of Wildlife Restoration and Alaska Dept. of Fish and Game; M.A. and H.S. British Columbia Ministry of Forests, Lands, Natural Resource Operations and Rural Development, Habitat Conservation Trust Foundation, Forest Enhancement Society of British Columbia; D.R.M and M.A. Polar Continental Shelf Project and National Geographic Society; M.L.J.G. the Office of the Director, National Institutes of Health under award number NIH T32OD010993; T.W. Ontario Ministry of Natural Resources and Forestry; B.L.B. National Park Service; A.K. GNWT Environmental Stewardship Fund. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
© 2021, The Author(s).
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