Tests de dépistage des ESST animales : présent et futur

Atypical scrapie/Nor98 in a sheep from New Zealand

In a consignment of sheep brains from New Zealand, to be used in Europe as negative control material in scrapie rapid screening test evaluations, brain samples from 1 sheep (no. 1512) gave the following initially confusing results in various screening tests: the brainstem repeatedly produced negative results in 2 very similar screening kits (enzyme-linked immunosorbent assay [ELISA]-1, ELISA-2), a macerate made from brainstem and cerebellum returned a clearly positive result in ELISA-2, and the macerate and a brainstem sample gave negative results in a third screening test (ELISA-3). In subsequent testing, cerebellum tissue alone tested strongly positive in ELISA-1 and produced a banding pattern very similar to atypical scrapie/Nor98 in a confirmatory Western blot (WB). The macerate showed weak staining in the confirmatory WB but presented a staining pattern identical to atypical scrapie/Nor98 in the scrapie-associated fibril WB. The latter test confirmed conclusively the first case of atypical scrapie/Nor98 in a sheep from New Zealand. Other parts of the brain either tested negative or very weak positive in ELISA-2 and in WBs, or tested with negative results by histopathology and immunohistochemistry. It appears that sheep no. 1512 is a case of atypical scrapie/Nor98 in which the abnormal prion protein was detected mainly in the cerebellum. This case emphasizes the need to retain brainstem, and cerebral and cerebellar tissues, as frozen and fixed materials, for conclusive confirmatory testing. Furthermore, consideration should be given to which screening method to use.

Differentiating blood samples from scrapie infected and non-infected hamsters by detecting disease-associated prion proteins using Multimer Detection System

This communication describes the application of a modified sandwich enzyme-linked immunosorbent assay (ELISA), termed Multimer Detection System (MDS) for the detection of disease-associated multimeric forms of the prion protein (PrPd) in hamster blood. PrPd was detected in plasma of prion-affected hamsters while MDS revealed no PrPd in identically-treated plasma of healthy animals. This is the first report of a single ELISA- based immune detection of PrPd from blood samples.

Biochemical identification of bovine spongiform encephalopathies in cattle

Important changes have occurred in the post-mortem diagnosis of bovine spongiform encephalopathy (BSE) in recent years. We have evaluated a commercially available Western blot method (TeSeE Wb) as a potential means of confirming BSE. This method was (i) highly sensitive, compared with a biochemical confirmatory Western blot method (AFSSA-Wb) previously used in France and (ii) more sensitive than two routinely used highly sensitive rapid tests (TeSeE ELISA, HerdCheck BSE). We show that this high sensitivity is mainly due to the antibody used (Sha31). Interestingly, TeSeE Wb was also able to diagnose the two currently recognised deviant BSE phenotypes (H-type and L-type or BASE). The initially described molecular features of these atypical forms of BSE were also readily recognised, although sensitivity of the method may be differently affected by the chosen Ab compared with typical BSE. This method is thus of potential interest for future evaluations of BSE confirmatory methods.