Diagnosis of rabies by polymerase chain reaction with nested primers.

A simple, sensitive, and specific polymerase chain reaction (PCR) protocol for detection of rabies virus is described. The process consists of sample preparation, reverse transcription, two-step DNA amplification, and detection of the amplified product. RNA was extracted from animal and human brain by phenol-chloroform using guanidinium thiocyanate. Viral RNA was then amplified in a two-step PCR that used two sets of nested primers designed to amplify rabies nucleocapsid (N) sequence. Rabies nucleocapsid sequence was amplified from all brain samples from 95 dogs and 3 humans with rabies confirmed by fluorescent antibody (FAT) and mouse inoculation tests (MIT). Rabies-negative brain samples (110 dogs, 2 humans) were PCR-negative. The process requires < 24 h. Detection of viral RNA was still possible in brain material that was left at room temperature for 72 h. As little as 8 pg of rabies virus RNA could be detected. This technique could have practical applications as a confirmatory test to FAT at busy rabies diagnostic centers.