Quantitation of Rabies Virus in Various Bovine Brain Structures

Bovine paralytic rabies (BPR) is a form of viral encephalitis that is of substantial economic importance throughout Latin America, where it poses a major zoonotic risk. Here, our objective was to utilize a laboratory protocol to determine the relative copy number of the rabies virus (RABV) genome in different bovine brain anatomical structures using quantitative real-time reverse transcription polymerase chain reaction (qRT-PCR). qRT-PCR quantifies the specific number of gene copies present in a sample based on fluorescence emitted after amplification that is directly proportional to the amount of target nucleic acid present in the sample. This method is advantageous owing to its short duration, reduced risk of contamination, and potential to detect viral nucleic acids in different samples more easily compared to other techniques. The brains of six rabid animals were divided into six anatomical structures, namely the Ammon's horn, cerebellum, cortex, medulla, pons, and thalamus. All brains were identified as positive for RABV antigens based on a direct immunofluorescence test. The same anatomical structures from the brains of four RABV-negative bovines were also assessed. RNA was extracted from each structure and used for qRT-PCR. An assay was performed to determine the copy numbers of RABV genes using an in vitro transcribed nucleoprotein gene. The standard curve used to quantify viral RNA exhibited an efficiency of 100% and linearity of 0.99. Analysis revealed that the cortex, medulla, and thalamus were the ideal CNS portions for use in RABV detection, based on the observation that these structures possessed the highest levels of RABV. The test specificity was 100%. All samples were positive, no false positives were detected. This method can be used to detect RABV in samples that contain low levels of RABV during diagnosis of BPR.