Mortality Causes in Free-Ranging Eurasian Brown Bears (Ursus arctos arctos) in Spain 1998–2018

Abstract

This work summarizes the mortality cases of twenty-five free-ranging Eurasian wild brown bears (Ursus arctos arctos) from the Cantabrian mountain range submitted for necropsy in Asturias and Castilla y León (northwestern Spain) from 1998 to 2018. Mortality cases were classified both caused by (i) “non-human intervention” or “human intervention” causes and based on (ii) “non-infectious” or “infectious” etiology. In four cases (16%) it was not possible to determine the cause of death due to the inadequate preservation of collected specimens or insufficient tissue availability. Based on “non-human intervention” or “human intervention” causes, fourteen of the 21 (66.7%) brown bears died as a consequence of “non-human intervention” due to traumatic lesions (fights, unknown traumas or infanticide), infectious canine hepatitis, neoplasia or mushroom poisoning. In contrast, seven (33.3%) brown bears died by “human intervention” due to illegal hunting (shooting or snare), handling (during transit in an attempt to reintroduce a bear back into the wild) or strychnine poisoning. Based on “non-infectious” or “infectious” etiology, twelve of the 21 (57.1%) brown bears died due to “non-infectious” causes, namely traumatic lesions such as shooting, snare, fighting or infanticide, handling, strychnine poisoning, mushroom poisoning or neoplasia. The remaining nine (42.9%) animals died due to “infectious” diseases which included gangrenous myositis, infectious canine hepatitis or septicemia. In six of those cases traumatic lesions caused by non-human or human activities were complicated with bacterial infection (clostridiosis and septicemia) which finally caused the death of those animals. Additionally, exertional myopathy was observed in the handled animal and in one bear found in a snare. In a free-ranging population of Eurasian brown bear from the Cantabrian mountain range, main causes of death are attributed to non-human related traumatic lesions and infectious diseases (primary developed such as infectious canine hepatitis or secondary developed such as clostridiosis or septicemia) which is in contrast to previously reported data for other bear populations. These data are valuable and may help in the conservation and management of this recovering population.

Fatal bacterial septicaemia after immobilisation of a captive brown bear (Ursus arctos)

“…Recently, C septicum was reported in a single wild brown bear after muscle damage, similar to other clostridial infections, such as C sordellii, C bifermentans, C chauvoei and C novyi. [1][2][3] Evidence of C septicum in a wild black bear (Ursus americanus) was associated with the immobilisation, just as in the present case in which C septicum is reported for the first time in a captive brown bear. 3 The aim of this report was to make veterinarians who work with zoo and wildlife animals aware of the fact that secondary bacterial infections after immobilisation can lead to death of Ursidae, with death occurring as early as 48 hours after infection with C septicum.…”

“…Recently, C septicum was reported in a single wild brown bear after muscle damage, similar to other clostridial infections, such as C sordellii , C bifermentans , C chauvoei and C novyi . 1–3 Evidence of C septicum in a wild black bear ( Ursus americanus ) was associated with the immobilisation, just as in the present case in which C septicum is reported for the first time in a captive brown bear 3…”

Wolf ( Canis lupus ) as canine adenovirus type 1 (CAdV‐1) sentinel for the endangered cantabrian brown bear ( Ursus arctos arctos )

“…Nevertheless, it seems that ICH is not a frequent cause of death in northwestern Iberian wolf populations, because the Asturian wolf population has recovered and maintained itself in recent decades (Blanco et al., 2008; García & Llaneza, 2012) and because we unaware of reports of clinical cases in the field. In contrast, a study of 21 brown bears in Asturias identified three that died of CAdV‐1, and all three animals showed clinical disease with consistent macroscopic and microscopic lesions (Balseiro et al., 2020; García Marín et al., 2018). Bears may be more vulnerable to severe infection and ICH, which could be related to their low genetic variability (García Marín et al., 2018).…”

“…The present study aimed to clarify the threat that CAdV‐1 may represent to bears and other carnivores by analysing the geo‐temporal distribution of CAdV‐1 in Asturias during a 10‐year period in wolves and to identify whether wolves may serve as a reservoir species that drives infections in bears and potentially other sympatric wild carnivores in the area. If so, wolves may be useful as CAdV‐1 sentinels because they can be sampled more easily than the endangered Cantabrian brown bear (Aguirre, 2009; Balseiro et al., 2020).…”

Non-invasive surveillance of shared pathogens in the Eurasian brown bear (Ursus arctos) human interface

“…Brown bears are especially susceptible to infectious diseases because of the features of their populations (i.e., small and relatively isolated/fragmented), as well as their behavior and ecology (i.e., apex consumer and facultative scavengers) [ 10 ]. Recently, infectious diseases have been identified as an important cause of death in this population (39.7% in the period 1998–2023) [ 11 , 12 ]. The pathogens reported included Clostridium spp., verotoxigenic Escherichia coli , Canine Adenovirus type 1 (CAdV-1), and Canine Distemper Virus (CDV) [ [11] , [12] , [13] , [14] ].…”