Role of reverse transcriptase polymerase chain reaction for the diagnosis of human rabies

Traditionally, rabies diagnosis is made by demonstration of rabies viral antigen by direct immunofluorescence (DIF) and mouse inoculation test (MIT). The present study was carried out to evaluate the role of reverse transcriptase-polymerase chain reaction (RT-PCR) in comparison with these conventional techniques for the diagnosis of rabies.

Skin biopsies, corneal impression smears and saliva sample were collected ante-mortem and brain tissue and CSF were collected post-mortem from ten clinically suspected rabies patients. DIF, Seller staining, MIT and RT-PCR were performed on the patients' samples for the diagnosis of rabies. The ability of RT-PCR to detect rabies virus earlier as compared to other assays was tested both for reference virus as well as clinical isolates.

All samples taken ante-mortem were negative for DIF test. Six of 10 post-mortem brain tissues of the clinically suspected patients were positive both by RT-PCR and MIT, of these six, five were positive by DIF test and four were positive by Seller stain. RT-PCR could detect the rabies virus earlier as compared to DIF, both from clinical isolates and fixed rabies virus.

The present results showed 100 per cent sensitivity and specificity of RT-PCR as compared to 83.3 per cent of DIF and 66.7 per cent of Sellers stain for diagnosis of rabies. RT-PCR also detected rabies viral infection earlier as compared to conventional tests and can also be used on ante-mortem samples. Thus, the present study shows the usefulness of RT-PCR as an alternative to MIT for the confirmation of rabies diagnosis.