Bear Health,
Parasites, and Disease
Key Points
The brown bear population in Scandinavia is generally healthy (i.e., they have relatively low prevalence of disease, parasites, and infections).
Bears are hosts for ticks that carry diseases, such as Lyme disease, that can affect human health; the prevalence of ticks and tick-borne diseases will likely increase as the climate changes.
Congenital deformities have been detected in the Scandinavian brown bear population, but instances appear to be rare.
Bears are known to have high levels of lead (Pb) in their blood, which may affect their health and behavior as well as affect human health when bear meat is consumed.
The population of brown bears in Scandinavia is generally a healthy one, meaning they are currently only minimally affected by pathological conditions such as parasites, disease, infections, and malformities (1). However, individual bear health can be influenced by multiple factors including interactions with other organisms and human activities. Understanding their health, including parasite loads and disease dynamics, is essential for effective conservation and management efforts, particularly in the context of climate change. For example, it helps us understand fundamental aspects of bear behavior as well as assess current and future risks to the population.
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​Parasites
Like many wild animals, bears can host a variety of internal and external parasites. Examples of internal parasites include gastrointestinal worms such as helminths and nematodes, while external parasites include ticks and fleas (1). Such parasites can affect bear health, particularly when infestations are severe. We know little about the internal parasite load of brown bears in Scandinavia, although external parasites have been observed. For example, chewing lice (Trichodectes spp.) were detected on two adult bears captured in 2014/2015, which caused extensive localized hair loss and skin discoloration (2). There is also evidence that ticks (Ixodes Ricinus) are prevalent in the bear population, especially in the more southern bear population where the climate is warmer and more suitable for ticks (3). This is important because ticks carry diseases, such as Lyme borreliosis and tick-borne encephalitis, which can affect both bear health but also spill over into human populations. Indeed, the prevalence of ticks and tick-borne diseases in wildlife populations is expected to increase at higher latitudes and elevations as the climate changes (4), which coincides with the incidence of tick-borne diseases in humans (5). Paillard, Jones (3) suggests that the long-term monitoring of large mammals, including bears, can provide insight into the shifting patterns of ticks and tick-borne diseases through time.
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​​Disease
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While brown bears can be susceptible to various diseases, in general, infectious disease is not a common cause of mortality for Scandinavian brown bears (6). This has been substantiated by various research accounts. For example, Ursids in general seem to have low susceptibility to prion diseases (7). Although rabies (a viral disease that can lead to aggressive or abnormal behavior and subsequent death in both infected animals and humans) has been observed in brown bears (1), there is no evidence that it is currently present in the Scandinavian population. However, research does suggest that Scandinavian bears have high levels of antibodies for to the causative agent of Lyme disease (Borrelia burgdorferi) but not tick-borne encephalitis (3), although it is unclear to what extent Lyme disease actually affects bear health. Examples of genetic defects have been observed in the population, although they are likely rare. For example, congenital hydrocephalus was detected in a cub who had the same father as his mother (8), a congenital heart defect was observed in an adult female (9), and an adult female was observed with 6 toes on the hind foot.
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Exposure to pollutants
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Like many wildlife species around the world, brown bears in Scandinavia may be exposed to pollutants and contaminants in their environment. These pollutants can originate from various sources including industrial activities, agriculture, and human settlements. One such pollutant is lead (Pb), which is a global health problem for both humans and wildlife. Lead is a highly toxic heavy metal that can disrupt a wide variety of biological functions in living organisms and is dangerous for both wildlife and humans (10). Recent research found high lead concentrations in the blood of Scandinavian brown bears, and suggests that the bear population is subject to life-long lead exposure which may negatively affect both individual and population health (11, 12). Importantly, lead exposure in brown bears may have direct consequences for human health when consumed (11, 13). For detailed information about lead exposure in the Scandinavian brown bear population, see Ecotoxicology: Lead (Pb) exposure in Scandinavian brown bears.
References
1. Swenson JE, Ambarli H, Arnemo J, Baskin L, Ciucci P, Danilov P, et al. Brown bear (Ursus arctos; Eurasia). Bears of the World: Ecology, Conservation and Management Cambridge University Press, Cambridg. https://www cambridge org/core/books/bears-of-the-world/brown-bear-ursus-arctoseurasia. 2020:139-61.
2. Esteruelas NF, Malmsten J, Bröjer C, Grandi G, Lindström A, Brown P, et al. Chewing lice Trichodectes pinguis pinguis in Scandinavian brown bears (Ursus arctos). International Journal for Parasitology: Parasites and Wildlife. 2016;5(2):134-8.
3. Paillard L, Jones KL, Evans AL, Berret J, Jacquet M, Lienhard R, et al. Serological signature of tick-borne pathogens in Scandinavian brown bears over two decades. Parasites & vectors. 2015;8(1):1-12.
4. Lindgren E, Tälleklint L, Polfeldt T. Impact of climatic change on the northern latitude limit and population density of the disease-transmitting European tick Ixodes ricinus. Environmental health perspectives. 2000;108(2):119-23.
5. Jore S, Viljugrein H, Hofshagen M, Brun-Hansen H, Kristoffersen AB, Nygård K, et al. Multi-source analysis reveals latitudinal and altitudinal shifts in range of Ixodes ricinus at its northern distribution limit. Parasites & vectors. 2011;4(1):1-11.
6. Mörner T, Eriksson H, Bröjer C, Nilsson K, Uhlhorn H, Ågren E, et al. Diseases and mortality in free-ranging brown bear (Ursus arctos), gray wolf (Canis lupus), and wolverine (Gulo gulo) in Sweden. J Wildlife Dis. 2005;41(2):298-303.
7. Stewart P, Campbell L, Skogtvedt S, Griffin KA, Arnemo JM, Tryland M, et al. Genetic predictions of prion disease susceptibility in carnivore species based on variability of the prion gene coding region. PloS one. 2012;7(12):e50623.
8. Kübber-Heiss A, Zedrosser A, Rauer G, Zenker W, Schmidt P, Arnemo JM. Internal hydrocephalus combined with pachygyria in a wild-born brown bear cub. European journal of wildlife research. 2009;55:539-42.
9. Ågren E, Söderberg A, Mörner T. Fallot's tetralogy in a European brown bear (Ursus arctos). J Wildlife Dis. 2005;41(4):825-8.
10. Bellinger DC, Burger J, Cade TJ, Cory-Slechta DA, Finkelstein M, Hu H, et al. Health risks from lead-based ammunition in the environment. National Institute of Environmental Health Sciences; 2013. p. a178-a9.
11. Fuchs B, Thiel A, Zedrosser A, Brown L, Hydeskov HB, Rodushkin I, et al. High concentrations of lead (Pb) in blood and milk of free-ranging brown bears (Ursus arctos) in Scandinavia. Environmental Pollution. 2021;287:117595.
12. Fuchs B, Joly K, Hilderbrand GV, Evans AL, Rodushkin I, Mangipane LS, et al. Heavy metals in arctic and sub-arctic brown bears: Blood concentrations of As, Cd, Hg and Pb in relation to diet, age and human footprint. Environmental Research. 2023;229:115952.
13. Hampton JO, Pain DJ, Buenz E, Firestone SM, Arnemo JM. Lead contamination in Australian game meat. Environmental Science and Pollution Research. 2023;30(17):50713-22.