PATHOLOGY OF WILD AMERICAN BLACK BEARS (URSUS AMERICANUS) FROM TENNESSEE AND THE GREAT SMOKY MOUNTAINS NATIONAL PARK, USA

Abstract

The southern Appalachians are home to a thriving population of American black bears (Ursus americanus), which are the most abundant and widely dispersed ursid in North America. As broad-ranging, long-lived, opportunistic omnivores, black bears are excellent sentinels for the health of their environment, yet there are limited studies on the health of bears in this region. In this study we describe pathologic findings of 120 bears from Tennessee and the Great Smoky Mountains National Park, USA, autopsied between and including 1980–2025. Euthanasia due to human-bear conflict was by far the most common cause of death (58.3%, 70/120) and was primarily due to food-conditioned behavior (32/70) or aggressive behavior exhibited during a human encounter (12/70) without apparent predisposing pathologic conditions. Trauma (19.2%, 23/120), usually attributed to vehicular collision (12/23) or gunshot wounds (5/23), and emaciation (7.5%, 9/120) were the next most common causes of death. Infectious, toxic, or congenital diseases were uncommon, and included pyothorax (n=2), bacterial endometritis (n=1), Angiostrongylus pneumonia (n=1), and bromethalin toxicosis (n=1; the first case with associated lesions in a black bear). Common lesions included dermatitis (64.5%, 40/62), nephritis (14.3%, 12/84), and idiopathic meningitis or encephalitis (12.2%, 10/87). Ursicoptes spp. mites, Rhabiditis (Pelodera) spp. nematodes, intravascular microfilaria, or intracorneal fungi variably accompanied dermatitis. Other important parasites identified in this study include the first confirmed cases of Trichinella spp. (n=2) in black bears of Tennessee, as well as several cases of Dirofilaria immitis (canine heartworm; n=3), including the second confirmed patent infection in a bear. This study establishes baseline pathologic data for a healthy black bear population and builds on previous knowledge of their diseases and pathogens, facilitating population management and rehabilitative care.