Raiva e encefalite viral eqüina no Semiárido Nordestino, Brasil.

Abstract

With the aim to study the distribution of lesions and the rabies virus in spontaneous cases of rabies in ruminants and to determine the efficiency of the direct immunofluorescent test (DIF), mouse inoculation (MI) and presence of Negri bodies in the diagnosis of the disease, 48 cases of the disease were examined. Samples of frontal, temporal, parietal and occipital cerebral cortex, hippocampus, thalamus, rostral and caudal colliculi, cerebellum, pons, medulla oblongata, basal nuclei and sections of the cervical, thoracic and lumbar spinal cord were examined. Of the 48 samples examined all were positive on DIF and MI, and in 30 (62.5%) Negri bodies were observed. However there were differences in the results of the three tests in the different regions of the central nervous system. In the samples of the cerebral cortex in 38 cattle, the frequency of inclusion bodies was low (11%-37%), and also the positivity to DIF and MI (60%-80%). In contrast, all samples of thalamus, pons and spinal cord were positive to DIF and MI. In other regions of the brain stem, positivity to these tests varied between 60% and 96.7%. On histologic examination, the major frequency of Negri bodies (88.2%) was observed in the cerebellum. In eight sheep the DIF and MI tests were positive in all sections of the CNS examined and Negri bodies were found in three animals. Only two goats were examined; both were positive in DIF and MI tests and in one Negri bodies were found. These results suggest that the recommendations of the Brazilian Technical Manual for Rabies of Herbivores is adequate for rabies diagnosis, because their recommendations include the histologic study and the examination of cerebellum, and sections of the brainstem with high positivity to DIF and MI tests. However, a better recommendation is to send for DIF and MI half of the brain cut longitudinally and samples of the spinal cord, which will permit to examine one or two sections, and if those are negative to return to the material and examine the rest of the sections. In contrast, to collect samples of the brain or half brain can be inappropriate for the diagnosis of other diseases of the CNS, for which the study of the whole fixed brain is necessary to recognize the symmetry or distribution of lesions. In these situations by the results obtained here, it can be recommended to send different sections of the spinal cord for DIF and MI tests and to fix the whole brain for gross and histologic examinations.