Rabies in a previously vaccinated horse: case report / Raiva em equino previamente vacinado: relato de caso

Rabies is an acute, progressive, and fatal encephalomyelitis caused by a Lyssavirus. Horses affected by the disease may be a source of infection for humans. A rapid diagnosis is crucial to initiate a prompt and adequate infection control and public health measures. This manuscript reports the case of a 4-year-old gelding, 370 kg, healthy and routinely used for veterinary teaching purposes that developed rabies although vaccinated against it. Clinical signs included lameness, ataxia, muscle tremors, decubitus and pedalling, progressive paralysis, profuse salivation, teeth grinding, and whinnying. After 4 days, the animal was euthanised and definitive diagnosis was achieved through an animal inoculation test which was positive. Complementary findings included encephalomyelitis with perivascular cuffs and identification of Negri bodies in various areas of the brain.(AU)

A raiva é uma encefalomielite aguda, progressiva e fatal causada por um Lyssavirus. Cavalos acometidos pela doença podem ser uma fonte de infecção para homens. O rápido diagnóstico é crucial para que iniciem medidas de controle de infecção e de saúde pública adequadas. Esse manuscrito descreve o caso clínico de um equino de 4 anos, macho castrado, 370 kg, hígido, usado nas práticas didáticas da escola de veterinária que desenvolveu quadro clínico de raiva, apesar de ser vacinado contra a referida doença. Os sinais clínicos incluíram claudicação, ataxia, tremores musculares, decúbito e movimentos de pedalagem, paralisia progressiva, salivação profusa, bruxismo e relinchos. Após 4 dias, o animal foi eutanasiado e o diagnóstico definitivo foi feito através de prova biológica positivada. Os achados complementares incluíram os achados histopatológicos nos quais destacam-se encefamolielite com manguitos perivasculares e identificação de Corpúsculos de Negri em várias áreas do cérebro.(AU)

Effect of Postmortem Degradation on the Preservation of Viral Particles and Rabies Antigens in Mice Brains. Light and Electron Microscopic Study.

Rabies diagnosis is mainly made on fresh brain tissue postmortem by means of the direct immunofluorescence test. However, in some cases, it is not possible to use this technique, given that the affected nervous tissue goes through a postmortem degradation process, due to problems in the handling and transport of the samples. For this reason, the preservation in time of the rabies virus inclusions was assessed, as well as the immunoreactivity and the ultrastructure of viral particles in tissue with postmortem degradation. Brains of mice inoculated with rabies virus and control mice were processed for conventional histology, immunohistochemistry, electron microscopy, and immunoelectron microscopy in different postmortem times. In the processed tissues for hematoxylin and eosin, the presence of eosinophilic inclusions was not observed beyond 12 h postmortem. Surprisingly, the immunoreactivity of the viral antigens increased with time, at least until 30 h postmortem. It was possible to easily recognize the viral particles by means of conventional electron microscopy until 12 h postmortem. Immunoelectron microscopy allowed us to identify the presence of viral antigens disseminated in the neuronal cytoplasm until 30 h postmortem, but immunoreactive viral particles were not observed. The rabies infection did not cause histological or ultrastructural alterations different from those in the control group as a result of the postmortem degradation. In conclusion, the immunohistochemistry is a reliable test for rabies diagnosis in samples with postmortem degradation and that have been fixed with aldehydes.