A comparative rabies laboratory diagnosis: peculiar features of samples from apparently healthy dogs in Nigeria

Many diagnostic methods have been used to detect rabies virus antigen. The preferred method for routine rabies diagnosis in fresh brain tissue is fluorescent antibody test (FAT). In this study, FAT was used to evaluate the presence of rabies virus antigen in the brain (hippocampus) of fifty apparently healthy dogs. Mouse inoculation test (MIT) and Microscopic examination for Negri bodies (MEN) were also employed to compare agreement, if any, between these employed methods. FAT detected 13 (26%), while MIT detected 10 (20%) samples positive for rabies virus antigen. Of the 10 samples positive by MIT only one sample was FAT negative all the remaining 9 samples were FAT positive. In all, 14 (28%) samples were positive by the two methods (FAT MIT) combined. Out of these, 3 (21.4%) were positive by MEN and only those samples with the 3+ distribution of fluorescing viral antigen by FAT as well as positive by MIT showed Negri bodies. Despite the high sensitivity of FAT and the good agreement (Kappa = 0.72) between the two methods; there is need to employ MIT on samples from apparently healthy dogs that showed FAT negative. MEN is not a reliable test for samples from apparently healthy dogs; but it was suggested that any sample from apparently healthy dog that is positive by FAT with 3+ or more distribution of fluorescing viral antigen should be presumed MEN positive.