Atypical cerebral listeriosis associated with Listeria innocua in a beef bull.

Natural infections of cattle associated with Listeria innocua have not been reported. This report describes the first case of cerebral listeriosis in a bull due to Listeria innocua. The animal presented neurological signs characterized by weakness, incoordination and recumbency. Histopathologic evaluation of brain tissue revealed multifocal microabscesses, perivascular lymphocytic cuffing, vasculitis, oedema and haemorrhages. All lesions extended from the medulla oblongata to the basal nuclei/parietal cortex area. Indirect immunohistochemistry labelled for Listeria sp. in the brain tissue, but not for Listeria monocytogenes, neurotropic Flaviviruses, BVDV, bovine Herpesvirus 1, Chlamydophila spp. and Histophilus somni. PCR was negative for ovine herpesvirus. L. innocua was isolated from brainstem and identified by biochemical tests (Camp and beta-hemolysis negative). Subsequently, the species was confirmed by a duplex PCR and minisequencing assays. L. innocua should be histologically considered as a differential diagnosis of thrombotic meningoencephalitis, malignant catarrhal fever and cerebral listeriosis due to L. monocytogenes in cattle.