Comparative study of the PrPBSE distribution in brains from BSE field cases using rapid tests

The distribution of PrPBSE in the brain of nine confirmed BSE field cases was analyzed using immunohistochemistry and compared to the levels of PrPBSE determined by two rapid tests (Prionics(R)-Check WESTERN and Prionics(R)-Check LIA). Each brain was dissected into 16 areas: spinal cord, medulla oblongata, pons, mesencephalon, thalamus, hippocampus, cerebellar vermis, cerebellar medulla, cerebellar hemispheres, occipital cortex, temporal cortex, parietal cortex, striatum, frontal cortex, piriform lobe and olfactory bulbs. The highest levels of PrPBSE were detected in the medulla oblongata, spinal cord and pons, and correspondingly both rapid tests showed 100% correlation with the immunohistochemistry with regard to sensitivity and specificity. Some inconsistencies between the levels of PrPBSE determined either by immunohistochemistry or by the rapid tests were found in brain areas with medium to low levels of PrPBSE. These brain areas included the cerebellar hemisphere, olfactory bulb, and the temporal and parietal cortices. A brain PrPBSE distribution curve (BPDC) was designed by plotting the PrPBSE signals obtained from the two rapid tests versus the anatomical region along the caudal-rostral axis of the brain. Comparison of the BPDC of the nine BSE cases showed that all cases had a similar PrPBSE distribution in the brain but with variable intensities, which could be explained by different stages in the progression of the disease. We propose that the BPDC could be used as a tool to differentiate classical cases of BSE from the recently identified atypical BSE cases.