Performance analysis of rapid diagnostic tests on atypical bovine spongiform encephalopathy

The preferred method to determine the prevalence of bovine spongiform encephalopathy (BSE) in a country is to use immunology-based rapid-tests. Though these tests are validated to detect C-type BSE disease–associated prion (PrPsc), test-specific properties may influence their ability to detect H- and/or L-type BSE PrPsc, where both are atypical from C-type PrPsc. Molecular characterization shows atypical BSE PrPsc to have a different sensitivity to proteinase activity and different affinities for certain prion-specific antibodies. It is important to understand how atypical BSE PrPsc may affect the performance of rapid-tests, which are typically dependant on the use of specific proteases and antibodies. The current study used experimentally generated C-, H-, and L-type BSE PrPsc to evaluate 3 tests used in various national BSE surveillance programs: an immunochromatographic assay, a standard sandwich enzyme-linked immunosorbent assay (stndELISA), and a PrPsc-conformation–specific ELISA (confELISA). Although BSE PrPsc type had some effects on rapid-test performance, analytical sensitivity for atypical BSE PrPsc on all 3 platforms was not significantly compromised. When testing for atypical BSE PrPsc, the 3 tests were able to meet the same requirements that the European Food Safety Authority set when evaluating the tests for C-type BSE PrPsc.

Properties of L-Type Bovine Spongiform Encephalopathy in Intraspecies Passages

The origin and transmission routes of atypical bovine spongiform encephalopathy (BSE) remain unclear. To assess whether the biological and biochemical characteristics of atypical L-type BSE detected in Japanese cattle (BSE/JP24) are conserved during serial passages within a single host, 3 calves were inoculated intracerebrally with a brain homogenate prepared from first-passaged BSE/JP24-affected cattle. Detailed immunohistochemical and neuropathologic analysis of the brains of second-passaged animals, which had developed the disease and survived for an average of 16 months after inoculation, revealed distribution of spongiform changes and disease-associated prion protein (PrPSc) throughout the brain. Although immunolabeled PrPSc obtained from brain tissue was characterized by the presence of PrP plaques and diffuse synaptic granular accumulations, no stellate-type deposits were detected. Western blot analysis suggested no obvious differences in PrPSc molecular mass or glycoform pattern in the brains of first- and second-passaged cattle. These findings suggest failures to identify differences in mean incubation period and biochemical and neuropathologic properties of the BSE/JP24 prion between the first and second passages in cattle.