Distribuição do vírus rábico no sistema nervoso central em ruminantes naturalmente infectados / Distribution of rabies vírus in the central nervous system in naturally infected ruminants

Com o objetivo de identificar a distribuição das lesões do vírus rábico no sistema nervoso central de casos espontâneos de raiva em ruminantes e comparar as técnicas de imunofluorescência direta (IFD), inoculação em camundongos (ICC) e presença de corpúsculos de Negri para o diagnóstico da doença foram analisados materiais proveniente de 48 casos de raiva, incluindo amostras de córtex frontal, temporal, parietal e occipital, hipocampo, tálamo, colículo rostral e caudal, cerebelo, ponte, medula oblonga, núcleo da base e porções da medula cervical, torácica e lombar. De 48 amostras analisadas, todas foram positivas na IFD e na ICC e em 30 (62,5 por cento) foram encontrados corpúsculo de Negri (CN). No entanto, houve diferenças importantes no resultados dos três testes nas diferentes regiões do SNC avaliadas. Nos cortes de córtex cerebral, em 38 bovinos, a presença de corpúsculos de inclusão foi baixa (11 por cento-37 por cento) assim como a positividade para IFD e ICC (60-80 por cento). Pelo contrário, todas as amostras de ponte, tálamo e medula testados foram positivas para IFD e ICC. Em outras regiões do tronco encefálico e também no cerebelo a positividade para ICC e IFD foi de 60 por cento a 96,7 por cento. No cerebelo foi encontrada a maior frequência (88,2 por cento) de corpúsculos de inclusão. Em oito ovinos as provas de ICC e IFD foram positivas em todos os cortes e foram observados corpúsculos de inclusão em três animais. Foram analisados somente dois casos de caprinos encontrando-se corpúsculos de inclusão em um e ambos foram positivos para IFD e ICC. Os resultados obtidos nesse trabalho sugerem que a conduta recomendada pelo Manual Técnico de Controle da Raiva dos Herbívoros (MTCRH) permite o diagnóstico de raiva associando o estudo histológico aos testes de IFD e ICC que incluem cerebelo, tálamo e tronco encefálico que apresentam alta positividade para as provas de IFD e ICC. No entanto, a melhor conduta é a de incluir metade do encéfalo cortado longitudinalmente e amostras de medula. Isto permite examinar por IFD e ICC uma ou mais regiões onde essas provas apresentam maior positividade e, posteriormente, se essas provas fossem negativas, retornar ao material original e examinar outras regiões. Por outro lado, a coleta de amostras dos locais recomendados pela MTCRH, assim com a coleta de metade do encéfalo, podem prejudicar o diagnóstico de outras doenças para o qual é necessário o estudo de todo o encéfalo após a fixação em formaldeído, para constatar a simetria e a distribuição das lesões. Nestes casos, com base nos resultados obtidos neste trabalho, pode ser recomendado para diagnóstico laboratorial de raiva o envio exclusivo de porções da medula cervical, dorsal e lombar, já que as três porções apresentaram 100 por cento de positividade nas provas de IFD e ICC. Além disso, o estudo histológico de todas as porções do cérebro incluídas neste trabalho permitirá complementar o diagnóstico.

With the aim to study the distribution of lesions the rabies virus in spontaneous cases of rabies in ruminants and to determine the efficiency of the direct fluorescent antibody test (DFA), mouse inoculation (MI) and presence of Negri bodies in the diagnosis of the disease, 48 cases of the rabies 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 DFA and MI, and in 30 (62.5 percent) Negri bodies were observed. However there were differences in the results of the three tests among 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 percent), and so was the positivity to DFA and MI (60-80 percent). In contrast, all samples of thalamus, pons and spinal cord were positive to DFA and MI. In other regions of the brain stem, positivity to these tests varied between 60 percent and 96.7 percent. On histologic examination, the major frequency of Negri bodies (88.2 percent) was observed in the cerebellum. In eight sheep the DFA and MI tests were positive in all sections of the CNS examined and Negri bodies were found in three sheep. Only two goats were examined; both were positive in DFA 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 DFA and MI tests. However, a better recommendation is to send for DFA 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 get back 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.

Prevalence and risk factors for anti-Toxoplasma gondii antibodies in goats of the Seridó Oriental microregion, Rio Grande do Norte state, Northeast region of Brazil.

The prevalence and risk factors for anti-Toxoplasma gondii antibodies were investigated in goats of the Seridó Oriental microregion, Rio Grande do Norte state, Northeast region of Brazil. Three hundred and sixty-six blood samples from goats collected by jugular venopuncture were used. For the serologic diagnosis of Toxoplasma gondii infection, the indirect fluorescent-antibody test (IFAT) with cut-off value 1:64 was carried out. The prevalence of anti-T. gondii antibodies was 30.6% [95% CI=25.9-35.6%] with titers ranging from 1:64 to 1:16,384. The multivariate logistic regression analysis showed that the risk factors associated to anti-T. gondii antibodies were presence of cats in the herd, extensive/semi-intensive management systems and lack of mineral supplementation.

Phylogenetic characterization of rabies virus isolates from Carnivora in Brazil.

The incidence of canine rabies has been widely reported in Brazil, and new rabies virus (RV) variants, genetically similar to canine RV, have recently been isolated from foxes. In order to derive the epidemiological characteristics of Brazilian Carnivora RV, Brazilian RVs isolated from dogs, cats, and foxes were genetically analyzed. Brazilian Carnivora RV isolates were divided into 2 main lineages. The predominant lineage was found in dogs and cats, which included the Argentinean and Bolivian Carnivora RV isolates, and was extensively distributed throughout Brazil and surrounding countries. The other lineage consisted of three sublineages containing Brazilian dog and fox RV isolates, with the dog sublineages located on an internal branch of 2 fox sublineages, suggesting that RV transmission events might have occurred between foxes and dogs in the past. These results suggest that contact between dogs and wildlife has the potential to generate new rabies variants and that it is important to control RV infection cycles in both dogs and wildlife to prevent spread of rabies infection.

Ticks (Acari: Ixodida) on wild carnivores in Brazil.

The present study reports field data of ticks infesting wild carnivores captured from July 1998 to September 2004 in Brazil. Additional data were obtained from one tick collection and from previous published data of ticks on carnivores in Brazil. During field work, a total of 3437 ticks were collected from 89 Cerdocyon thous (crab-eating fox), 58 Chrysocyon brachyurus (maned wolf), 30 Puma concolor (puma), 26 Panthera onca (jaguar), 12 Procyon cancrivorus (crab-eating raccoon), 4 Speothos venaticus (bush dog), 6 Pseudalopex vetulus (hoary fox), 6 Nasua nasua (coati), 6 Leopardus pardalis (ocelot), 2 Leopardus tigrinus (oncilla), 1 Leopardus wiedii (margay), 1 Herpailurus yagouaroundi (jaguarundi), 1 Oncifelis colocolo (pampas cat), 1 Eira barbara (tayara), 1 Galictis vittata (grison), 1 Lontra longicaudis (neotropical otter), and 1 Potus flavus (kinkajou). Data obtained from the Acari Collection IBSP included a total of 381 tick specimens collected on 13 C. thous, 8 C. brachyurus, 3 P. concolor, 10 P. onca, 3 P. cancrivorus, 4 N. nasua, 1 L. pardalis, 1 L. wiedii, 4 H. yagouaroundi, 1 Galictis cuja (lesser grison), and 1 L. longicaudis. The only tick-infested carnivore species previously reported in Brazil, for which we do not present any field data are Pseudalopex gymnocercus (pampas fox), Conepatus chinga (Molina's hog-nosed skunk), and Conepatus semistriatus (striped hog-nosed skunk). We report the first tick records in Brazil on two Felidae species (O. colocolo, H. yagouaroundi), two Canidae species (P. vetulus, S. venaticus), one Procyonidae species (P. flavus) and one Mustelidae (E. barbara). Tick infestation remains unreported for 5 of the 26 Carnivora species native in Brazil: Oncifelis geoffroyi (Geoffroy's cat), Atelocynus microtis (short-eared dog), Pteronura brasiliensis (giant otter), Mustela africana (Amazon weasel), and Bassaricyon gabbii (olingo). Our field data comprise 16 tick species represented by the genera Amblyomma (12 species), Ixodes (1 species), Dermacentor (1 species), Rhipicephalus (1 species), and Boophilus (1 species). Additional 5 tick species (3 Amblyomma species and 1 species from each of the genera Ixodes and Ornithodoros) were reported in the literature. The most common ticks on Carnivora hosts were Amblyomma ovale (found on 14 host species), Amblyomma cajennense (10 species), Amblyomma aureolatum (10 species), Amblyomma tigrinum (7 species), Amblyomma parvum (7 species), and Boophilus microplus (7 species).

Seroprevalence of Toxoplasma gondii antibodies from wild canids from Brazil.

The prevalence of anti-Toxoplasma gondii antibodies was evaluated by the indirect immunofluorescent-antibody test in serum of 57 wild canids from three different species: Lycalopex gymnocercus, Cerdocyon thous and Dusicyon vetulus from the northeast, southeast and southern regions of Brazil. The prevalence was 35.1%, with 20 of the 57 canids demonstrating antibodies anti-T. gondii at dilutions of 1:16 in 2, 1:32 in 4, 1:64 in 2, 1:128 in 2, 1:256 in 6, 1:512 in 2 and 1:2048 in 2 animals. None of the D. vetulus were positive. Among the L. gymnocercus 11 (91.7%) of the 12 samples were positive and among C. thous 9 (60%) of the 15 had antibodies anti-T. gondii.