Increased pathogen exposure of a marine apex predator over three decades

Abstract

Environmental changes associated with global warming create new opportunities for pathogen and parasite transmission in Arctic wildlife. As an apex predator ranging over large, remote areas, changes in pathogens and parasites in polar bears are a useful indicator of changing transmission dynamics in Arctic ecosystems. We examined prevalence and risk factors associated with exposure to parasites and viral and bacterial pathogens in Chukchi Sea polar bears. Serum antibodies to six pathogens were detected and prevalence increased between 1987-1994 and 2008-2017 for five: Toxoplasma gondii, Neospora caninum, Francisella tularensis, Brucella abortus/suis, and canine distemper virus. Although bears have increased summer land use, this behavior was not associated with increased exposure. Higher prevalence of F. tularensis, Coxiella burnetii, and B. abortus/suis antibodies in females compared to males, however, could be associated with terrestrial denning. Exposure was related to diet for several pathogens indicating increased exposure in the food web. Elevated white blood cell counts suggest a possible immune response to some pathogens. Given that polar bears face multiple stressors in association with climate change and are a subsistence food, further work is warranted to screen for signs of disease.

Fig 1. Locations of Chukchi Sea polar bears sampled during two time periods: 1987–1994 and 2008–2017.

Population boundaries are based on the International Union for the Conservation of Nature (IUCN) Polar Bear Specialist Group (PBSG) designations.

Fig 2. Comparison of the percent of adult and subadult Chukchi Sea polar bears identified as exposed to six pathogens between 1987–1994 and 2008–2017.

Asterisks identify differences that were significant (p < 0.1) in a binary logistic regression (CDV = canine distemper virus).

Fig 3. Comparison in seropositivity of six pathogens for contemporary Chukchi Sea polar bears (this study) in comparison to other populations for which data are available (Southern Beaufort Sea) [23, 43, 65, 99]; Western Hudson Bay [24]; Barents Sea [63; 106]; East Greenland [106, 107], and Baffin Bay [106].