An evaluation of immunofluorescence and PCR methods for detection of rabies in archival Carnoy-fixed, paraffin-embedded brain tissue.

Direct immunofluorescence and PCR detection methods were compared for sensitivity in evaluating the rabies status of archival specimens of Carnoy-fixed, paraffin-embedded brain tissue. The material consisted of 23 samples obtained during a rabies outbreak in Finland in 1988, and one sample isolated from a bat researcher who died of rabies in Finland in 1985. These results were compared with the original diagnoses performed on the fresh tissues. The immunofluorescence assay detected 100% (12/12) of the rabies-positive archival cases. A PCR assay designed to detect a 139-bp target near the 5' end of the rabies nucleoprotein gene also detected 100% (12/12) of the samples identified as positive in the fresh tissue specimens. A PCR assay designed to detect a 304-bp target spanning the 139-bp target of the first assay detected only 67% (8/12) of the original cases. No false positives were recorded. Both immunofluorescence detection of antigen and PCR detection of a short region of the nucleoprotein gene are useful in determining the rabies status of fixed, paraffin embedded (archival) material.