Diseases of the central nervous system (CNS) are often reported in cattle in Brazil. Although the State of Minas Gerais has the second largest cattle herd in the country, there is little information from this state concerning neurological diseases that affect cattle. The Laboratório de Saúde Animal of the Instituto Mineiro de Agropecuária (LSA/IMA) is in charge of the diagnosis of neurological diseases of livestock in the State, with emphasis on rabies and transmissible spongiform encephalopathies. A retrospective study was conducted on data from cattle with neurologic diseases evaluated by the LSA/IMA from January/2003 to June/2010, aiming to determine the profile of CNS samples sent for analysis, with emphasis on the diagnosis of bovine rabies. Issues related to the animal (sex, age, breed and type of death) as well as to the sample (method of conservation, person in charge the collection, and region of the CNS sampled) were evaluated. Data on frequency of rabies positive samples were analyzed by Fisher's exact test. During the period studied, 3,731 samples from cattle with neurological signs were analyzed, with a predominance of females and crossbred cattle. The method of preservation was the main problem encountered with only 25.89% of samples sent both refrigerated and fixed in 10% formaldehyde. There was a gradual decrease in submission of samples during the course of this study. All 3,703 samples were evaluated by direct fluorescent antibody test (DFA) and biological test (BT) for rabies, 41.58% being positivity for rabies, and 282 of those samples being subjected to histopathology examination. The frequency of positivity was influenced by breed, age, and type of death. Composition of the sample significantly influenced the results, with higher frequency of positivity in samples containing three or more CNS fragments by DFA, BT, or histopathology. The medulla, which is the fragment of choice for diagnosis of BSE, has often been mistakenly submitted under refrigeration, but not in 10% formalin. Cerebellum, thalamus, brain stem, and spinal cord had higher frequency of Negri bodies than the cerebral cortex and trigeminal ganglia. The nonsuppurative inflammatory infiltrate was less frequent in the cerebral cortex than in other CNS fragments. In conclusion, CNS samples from cattle with neurological syndrome sent to the animal health protection service of Minas Gerais are heterogeneous, and the preservation method was the major problem hindering and adequate diagnosis. In addition, diagnosis of rabies was influenced by parameters of the animal as well as the CNS sample. Submission of properly preserved fragments from various segments of the CNS contributes to a more accurate diagnosis of rabies in cattle.
Central nervous system; rabies; cattle; Minas Gerais