Fatal hepatic sarcocystosis in a free-ranging grizzly bear cub associated with Sarcocystis canis–like infection

Abstract

We describe herein fatal hepatic sarcocystosis in a free-ranging grizzly bear (Ursus arctos horribilis) cub with apicomplexan infection of the liver and brain, both demonstrating 100% homology for Sarcocystis canis and S. arctosi. Fatal hepatic sarcocystosis in dogs has been etiologically associated with intrahepatic schizonts of S. canis. In black and polar bears, a S. canis-like organism produces schizonts in the liver and massive hepatic necrosis. Although intramuscular sarcocysts, taxa S. arctosi and S. ursusi, have been described in healthy brown and black bears, respectively, they have not been detected in bears with hepatic sarcocystosis, to our knowledge, and it is currently unknown whether bears represent an aberrant or intermediate host.

Sarcocystis neurona Transmission from Opossums to Marine Mammals in the Pacific Northwest

“…Molecular sequencing at the ITS1 gene showed that one harbor seal (HS7) was infected with S. pinnipedi, a novel Sarcocystis species that was implicated as a cause of necrotizing hepatitis and associated mortality in ringed seals, Pacific walrus (Odobenus rosmarus divergens), bearded seal (Erignathus barbatus), spotted seal (Phoca largha) and gray seals (Halichoerus grypus) (Haman et al 2015). Previous work has suggested a close evolutionary relationship between S. pinnipedi and S. canis, which has been described in dogs and bears (Dubey et al 2006a, b;Britton et al 2019;Davies et al 2011). Sarcocystis pinnipedi was initially isolated in gray seals after a mass mortality event in Nova Scotia, Canada in March 2012.…”

Molecular characterization of Sarcocystis spp. as a cause of protozoal encephalitis in a free-ranging black bear

“…10 The brain of a third case had neither lesions nor schizonts, but was also PCR positive. 6 These previous reports suggest that the brain may be a predilection site for Sarcocystis spp. in bears, but infection does not always manifest as encephalitis.…”

“…Interestingly, gliosis was also present in the brain of 3 of the 4 cases in which the brain was examined histologically, although visible schizonts were not identified. 6,10,16 In one of these cases with gliosis but no visible schizonts, brain tissue was PCR positive for Sarcocystis spp. 10 The brain of a third case had neither lesions nor schizonts, but was also PCR positive.…”

“…22 Asexual life cycle phases occur in intermediate hosts, resulting in sarcocyst formation in striated muscle and less commonly the central nervous system and liver. 6,22 Sarcocysts contain thousands of bradyzoites that, when ingested by the carnivorous definitive host, undergo sexual lifecycle stages to produce infective oocysts that pass in the feces, thus completing the life cycle. 22 As is typical for most Sarcocystis spp., knowledge of the life cycle of S. canis, including identification of the definitive host, is incomplete.…”

“…12,16 Previous cases described in the literature used 100% similarity of partial but discriminatory regions of the 18S gene (DQ146148). 6,10 The 100% homology of 994 bp of the 18S gene of the S. canis-like parasite in polar bear (DQ146148) to sarcocysts in grizzly bears in Alaska currently described as S. arctosi (EF564590) suggests these may be the same etiologic agent. 11 Although S. canis was originally described from parasitic schizonts associated with fatal hepatitis in dogs, no DNA has yet been derived from infected dogs.…”