Viruses in unexplained encephalitis cases in American black bears (Ursus americanus)

Abstract

Viral infections were investigated in American black bears (Ursus americanus) from Nevada and northern California with and without idiopathic encephalitis. Metagenomics analyses of tissue pools revealed novel viruses in the genera Circoviridae, Parvoviridae, Anelloviridae, Polyomaviridae, and Papillomaviridae. The circovirus and parvovirus were of particular interest due to their potential importance as pathogens. We characterized the genomes of these viruses and subsequently screened bears by PCR to determine their prevalence. The circovirus (Ursus americanus circovirus, UaCV) was detected at a high prevalence (10/16, 67%), and the chaphamaparvovirus (Ursus americanus parvovirus, UaPV) was found in a single bear. We showed that UaCV is present in liver, spleen/lymph node, and brain tissue of selected cases by in situ hybridization (ISH) and PCR. Infections were detected in cases of idiopathic encephalitis and in cases without inflammatory brain lesions. Infection status was not clearly correlated with disease, and the significance of these infections remains unclear. Given the known pathogenicity of a closely related mammalian circovirus, and the complex manifestations of circovirus-associated diseases, we suggest that UaCV warrants further study as a possible cause or contributor to disease in American black bears.

Detection and Complete Genome Analysis of Circoviruses and Cycloviruses in the Small Indian Mongoose (Urva auropunctata): Identification of Novel Species

“…ictvonline.org/ictv-reports/ictv_online_report/ssdna-viruses/w/circoviridae, accessed 10 July 2021]. Circoviruses and cycloviruses have been reported in various mammals, birds and arthropods [1][2][3][4][5][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23]. Circoviruses have also been detected in fish and reptiles [2,[23][24][25][26][27][28].…”

“…Based on genome-wide pairwise nt sequence identities and phylogenetic analysis, the International Committee on Taxonomy of Viruses (ICTV) has recognized at least 49 and 52 species within the genera Circovirus and Cyclovirus , respectively [ , accessed 10 July 2021]. Circoviruses and cycloviruses have been reported in various mammals, birds and arthropods [ 1 , 2 , 3 , 4 , 5 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 ]. Circoviruses have also been detected in fish and reptiles [ 2 , 23 , 24 , 25 , 26 , 27 , 28 ].…”

Circovirus in Blood of a Febrile Horse with Hepatitis

“…Circoviruses are small viruses in the Circoviridae family whose circular single-stranded DNA genomes of~2 kb are amongst the smallest known [1]. Circoviruses are associated with a wide spectrum of disease ranging from asymptomatic to lethal in different birds, pigs, elks, cows, dogs, panda bears, bears, bobcats, pumas, foxes, minks, palm civets, fur seals, numerous rodents, as well as in reptiles and fish [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. Circoviruses have also been described in numerous bat species [21][22][23][24][25][26][27][28].…”

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

“…4,7,15 Metagenomic investigation of free-ranging black bears with idiopathic encephalitis has identified a range of novel viruses, including Ursus americanus circovirus. 2 It is unclear if any of the aforementioned pathogens cause encephalitis or other clinical illness in freeranging bears. There is also a single case of noninfectious encephalitis described in a captive polar bear caused by antibodies to NMDA (N-methyl-D-aspartate) receptors.…”

“…infection may cause fatal encephalitis in free-ranging bears, and may be considered a differential diagnosis for idiopathic nonsuppurative encephalitis in these species. 2 The health of free-ranging black bear populations is affected by multiple factors, including habitat loss and human-wildlife conflict. There is growing interest in the impacts of these and other cumulative stressors such as climate change on wildlife, including bears; however, the impacts of infectious disease require further investigation.…”