Blindness in a wild American black bear cub (Ursus americanus)

Abstract

An approximately six-month-old wild American black bear (Ursus americanus) was found wandering in Saskatchewan and was presented to the Veterinary Medical Centre of the Western College of Veterinary Medicine for apparent blindness. Clinical examination confirmed an inability to navigate a photopic maze, bilateral tapetal hyper-reflectivity, fundi devoid of retinal vessels, and small pale optic nerve papillae. Single-flash electroretinography revealed A and B-wave amplitudes of approximately 40 and 140 microvolts, respectively, in both eyes. Histologic abnormalities included bilateral optic papillary mineralization and bilateral segmental optic nerve degeneration, with occasional intralesional lymphocytes confirmed with immunohistochemistry for CD3+. There was also bilateral multifocal retinal dysplasia, gliosis, lymphocytic retinitis, a complete lack of retinal blood vessels, an intravitreal vascular membrane, and a mild lymphocytic-plasmacytic uveitis with small pre-iridal cellular membranes. The presence of a positive ERG in a blind bear with numerous retinal ganglion cells and degenerative changes in the optic nerve are most consistent with vision loss due to optic nerve injury, which given the young age of the bear likely occurred during ocular development. The presence of ocular inflammation suggests this injury resulted from an inflammatory/infectious process. The etiology could not be determined. Hepatic concentrations of vitamin A were within the normal reference range for domestic species. Pan-herpesvirus PCR and immunohistochemistry for canine distemper virus and Toxoplasma gondii were negative, although this does not rule out these or other infectious etiologies. This represents the first case report of neonatal or congenital ocular abnormalities in an ursid species.

Identification of gammaherpesvirus infection in free-ranging black bears (Ursus americanus)

“…A nonsuppurative encephalitis was identified in these animals via histopathology, but at this time, the causative agent remains unclear. However, during this investigation, herpesviruses were considered a potential cause, as ursine encephalitis cases have been linked to alphaherpesviruses (Dombrowski et al, 2016). Investigations using degenerate PCR primers, both at the OVDL and at Michigan State University VDL, resulted in amplification of DPOL DNA sequences with homology to gammaherpesviruses in a variety of tissues and in bears with and without evidence of neurologic disease.…”

“…Herpesvirus infection in bears has rarely been documented. Recovery of viral sequences corresponding to the alphaherpesviruses, such as equine herpesvirus 1 (EHV1) and equine herpesvirus 9 (EHV9), have been published in case reports involving captive ursid mortalities (Dombrowski et al, 2016). An investigation of squamous cell carcinomas revealed the presence of a gammaherpesvirus in multiple captive sun bears (Heloarctos malayanus) (Lam et al, 2013).…”

Progressive visual loss and severe retinal degeneration in a captive Kodiak bear (Ursus arctos mittendorfi)

“…The Kodiak bear ( Ursus arctos mittendorfi ) has an optic disc that is small, round and non‐myelinated 3. However, to the authors’ knowledge, ocular disease in the ursid species is poorly reported on, with only chronic keratitis,4 nodular fasciitis5 and a single case of congenital multifocal retinal dysplasia and retinitis described 6…”

“…Progressive hereditary retinal degeneration have also been documented in a number of species,10 16 25 with some species having specific genetic mutations identified that are predisposing 25 26. Finally, there are reports in many species, including another ursid, the American black bear ( Ursus americanus ) of bilateral symmetrical retinal degenerations of unknown aetiology 6 27–29…”

Surgical removal of cataract in an Asiatic black bear (<i>Ursus thibetanus</i>) by phacoemulsification and aspiration

“…There are few scientific reports about ocular diseases in the bears [2,10,12]. Hartley reported about ocular disease in bear [6].…”