Aspectos histopatológicos e imuno-histoquímicos da raiva em raposas Cerdocyon thous Histopathological and Immunohistochemical Aspects of Rabies in foxes Cerdocyon thous

Background: Several wild canids are considered reservoirs of rabies virus in the Northeast of Brazil, two wild canids have been reported as reservoirs of rabies virus Cerdocyon thous (crab-eating fox) and Pseudalopex vetulus (hoary fox) (previously called Dusicyon vetulus). The diagnosis of rabies in foxes is usually performed through fluorescent antibody test (FAT) and mouse inoculation test (MIT). However, until the moment, there are no detailed histopathological and immunohistochemical (IHC) description studies in foxes affected by this disease studies. Therefore, the aim of this work was the characterization of pathological and IHC findings of foxes with rabies sent to the Laboratory of Animal Pathology (LPA) of the Federal University of Campina Grande (UFCG) in Patos, semiarid region of Paraiba, Brazil. Case: Two foxes were sent to the LPA, phenotypic species identification through analysis of morphological aspects was performed and posteriorly necropsied. Fragments of organs of the thoracic and abdominal cavities, salivary glands, eye and Gasser ganglia were collected in addition to the central nervous system (CNS) that was collected integer and fixed at 10% buffered formalin. Later, serial sections of the 16 fragments of the CNS were performed, measuring about 0.5 cm thick and cleaved. Fragments of cerebrum, cerebellum, brainstem, spinal cord and salivary glands were sent to performing FAT and MIT. Paraffin blocks with fragments of the hippocampus were selected and submitted to IHC. Macroscopically, the two foxes had multiple skin lacerations, bone fractures and ruptures of abdominal organs from injuries. The vessels of the meninges were slightly congested. Histologically, the CNS had diffuse non-suppurative encephalitis, with inflammatory infiltrate composed primarily by lymphocytes and plasma cells, forming mononuclear perivascular cuffing, and gliosis associated with mild eosinophilic intracytoplasmic inclusion corpuscles primarily in neurons of the cortex, basal ganglia, hippocampus, thalamus, colliculi, bridge, obex and cerebellum. Meningitis and mild myelitis non-suppurative were also observed in both cases with rare viral inclusions in spinal cord neurons. Similar inflammation was also observed in the Gasser ganglion and in others peripheral nerve ganglia. Adrenal and salivary glands showed multifocal areas of moderate mononuclear inflammatory infiltrate composed mainly by macrophages and plasma cells. Strong positive IHC labeling was observed for rabies in the neurons in different brain regions, especially in the cerebral cortex and in Purkinje cells of the cerebellum. In both cases the diagnosis of rabies was confirmed by immunofluorescence and mouse inoculation. Discussion: The diagnosis of rabies in foxes was conducted through the characteristic histopathologic findings of the disease observed in the CNS and confirmed by the FAT, MIT and IHC. Although the histopathological findings in foxes are similar to what is observed in other species, the severity of inflammatory lesions and the large amount of inclusion bodies in the nervous tissue is an outstanding feature, regardless of the inflammatory response. The diagnosis of rabies in foxes can be achieved by characteristic histopathologic findings of the CNS, supported by evaluating peripheral nerve ganglia, salivary glands and adrenal which may also present similar microscopic lesions. Auxiliary Laboratory tests must be performed, such as FAT, MIT and IHC for confirmation of the disease.