Comparison between immunohistochemistry and two PCR methods for detection of Neospora caninum in formalin-fixed and paraffin-embedded brain tissue of bovine fetuses

The objective of this study was to identify the presence of the parasite by comparing immunohistochemistry (IHC) with two polymerase chain reaction (PCR) methods for the detection of the pNc5 gene and the internal transcribed spacer 1 (ITS1) of N. caninum in brain tissue of bovine fetuses that had previously been fixed in formalin and paraffin-embedded. In 29 out of 48 brains (60.4%), microscopic lesions consistent with Neospora infection were observed, and 21 of the 29 cases (72.41%) were positive for IHC. Fifteen of the 29 cases positive for IHC (51.72%) were also positive on the ITS1 PCR, and 12 cases were also positive on the pNc5 PCR (41.37%). The sensitivity of the PCR assays was 71.42% and 57.14%, respectively, and the specificity was 100% for both. The concordance between histopathology and IHC and the ITS1 PCR was 85%, and in the case of the pNc5 PCR it was 77.5%. When the number of fetuses positive by IHC and both PCR tests was compared, no statistically significant difference was found (P > 0.05). It is concluded that the use of formalin-fixed and paraffin-embedded bovine fetal tissues allows the detection of N. caninum by IHC or PCR. Nevertheless, it is recommended that more than one technique is used to increase the diagnostic sensitivity, and preferably tests that show better performance in the individual laboratory should be selected.