Raiva em bovinos diagnosticados no Setor de Patologia Veterinária da UFRGS, Porto Alegre, RS, Brasil no período de 2002 a 2007
Pedroso, Pedro Miguel OcamposLeal, Juliano de SouzaDalto, André Gustavo CabreraOliveira, Luiz Gustavo Schneider deDriemeier, David
Background: Rabies is a zoonotic disease caused by rabies virus, the genus Lyssavirus e family Rhabdoviridae. The commonest way of rabies transmission is by the bite of an infected mammal. Bites by rabid animals generally inoculate virus-laden saliva through the skin into muscle and subcutaneous tissues. Rabies has previously been regarded as 100% lethal. In South America, rabies in cattle is transmitted by vampire bats Desmodus rotundus mainly resulting in a major economic problem and public health. The present study retrospectively analyzed data from cattle affected by rabies registered between 2002 and 2007, evaluating the epidemiological, clinical and pathological and immunohistochemistry studies. Materials, Methods & Results: This retrospective study included epidemiological, clinical, pathological, direct immunofluorescence, and immunohistochemistry findings from 26 cattle affected by rabies diagnosed by the Laboratory of Veterinary Pathology, UFRGS, Porto Alegre, RS, Brazil in the period from 2002 to 2007. The samples were selected from a histological diagnosis of lesions characteristic of rabies or positive direct immunofluorescence for rabies where samples were available for histological examination. The central nervous system (CNS) samples of cattle were reported in 10% formalin fixed, routinely processed for histology, embedded in paraffin, cut at 5 µm and stained with hematoxylin-eosin. Histological slides were also tested with immunohistochemistry procedure using a standardized protocol for rabies with a polyclonal primary antibody at a dilution of 1:1000 in phosphate buffered saline. Cattle between 3 months and 8 years of age were affected. Clinical course ranged from 1-10 days. Paralytical form was the most common. Clinical signs included motor incordination, paresis, and paralysis of the pelvic members and decubitus. The main histopathological findings were characterized by lymphoplasmacytic meningoencephalitis and nonsuppurative meningomyelitis associated with characteristic intracytoplasmic inclusion bodies in 88.4% (23/26) cases. In 92.3% (24/26), the animals examined were positive by immunohistochemistry for rabies. Positive labeling was present in perikarya of neurons as aggregates of granules or round formations associated with varying numbers of inclusion bodies, mainly observed in the Purkinje neurons of the cerebellum. Discussion: Rabies is an important disease of cattle in Brazil. In this study the diagnosis was based on the histopathological, direct immunofluorescence and positive immunostaining for rabies antigen. Immunohistochemistry is a laboratory technique that uses specific antibodies for visualization and evaluation as to the quantity, distribution and cellular localization of epitopes in histological sections, allowing the use of formalin-fixed tissues, which facilitates the transport of samples to the Laboratory, generating more time for sending. The average markup of 26 cases of cattle was 92.3%, but this average could be higher if other areas of the CNS had been used and the fixation time in formalin were lower. Immunohistochemistry is an important auxiliary tool for the diagnosis of rabies, especially in circunstances in which refrigeration cannot be adequately maintained, and in cases characterized by nonsuppurative meningoencephalitis with absence of inclusion bodies.
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