Molecular characterization and diagnostic investigations of rabies encephalitis in camels (Camelus dromedaries) in Oman: a retrospective study.

The accurate and early diagnosis of rabies is critical for undertaking public health measures in animals. The aim of the current study was to identify the molecular characterization of the circulating rabies virus (RABV) among camels (Camelus dromedaries) in Oman and to evaluate the efficacy of the histopathology and reverse transcription polymerase chain reaction (RT-PCR) as diagnostic tools of acute rabies encephalitis in camels in comparison with direct fluorescent antibody test (dFAT). Of the forty-five brain samples from suspected camels submitted to the Animal Health Research Center in Oman (2009-2013), 22 cases were positive by dFAT and RT-PCR. Two positive samples were subjected for N gene nucleotide sequencing and phylogenetic analysis (accession numbers GU353156 and KC883998 for brain samples collected in 2009 and 2011, respectively). The specificity and sensitivity of histopathology were 100% and 81%, respectively, while in RT-PCR were 100% and 100%, respectively. The neuropathological changes were presence of intracytoplasmic inclusions (Negri bodies) in the pyramidal neurons of the hippocampus beside prominent cerebral and cerebellar congestion and hemorrhage. Neuronal necrosis with satellitosis and neuronophagia were also noticed in the cerebrum of affected brains. Conclusively, there was one genetic group of RABV with 99% homology circulating in Omani camels. Also, it is concluded that histopathological examination is a safe and reliable diagnostic tool when only formalin-fixed and paraffin-embedded material is available, but the negative results should be reaffirmed by dFAT or RT-PCR.