Comparative study of immunoassays, a microelectromechanical systems-based biosensor, and RT-QuIC for the diagnosis of chronic wasting disease in white-tailed deer

Background: Chronic wasting disease (CWD) is a fatal transmissible spongiform encephalopathy in cervids. The disease is caused by a pathogenic prion, namely PrP^Sc. Currently, diagnosis of CWD relies on IHC detection of PrP^Sc in the obex or retropharyngeal lymph nodes (RPLN) or ELISA screening of obex and RPLN followed by IHC confirmation of positive results. In this study, we assessed the performance characteristics of two immunoassays: CWD Ag-ELISA and TeSeE ELISA, RT-QuIC, and MEMS biosensor via testing 30 CWD + and 30 CWD- white-tailed deer RPLN samples.

Results: Both CWD Ag-ELISA and TeSeE ELISA correctly identified all CWD + and CWD- samples. A greater intra-assay coefficient of variation (CV) in S/P ratios was observed for the TeSeE ELISA (16.52%), compared to CWD Ag-ELISA (9.49%). However, the high CV did not affect the qualitative results of triplicate assays when the corresponding manufacturer's cutoff was used. The MEMS biosensor not only correctly identified all CWD + and CWD- RPLN samples, but also demonstrated a 100% detection rate for all CWD + samples at dilutions from 10^{- 0} to 10^{- 3}. Evaluation of RT-QuIC indicated that the rate of false negative reactions decreased from 21.98% at 10^{- 2} dilution to 0% at 10^{- 4} and 10^{- 5} dilutions; and the rate of false positive reactions reduced from 56.42% at 10^{- 2} dilution to 8.89% and 2.22% at 10^{- 4} and 10^{- 5} dilutions, respectively. Based on a stringent threshold of 2 x the first 10 fluorescent readings of each well and a final cutoff of 2/3 positive reactions for each sample, RT-QuIC correctly identified all positive and negative samples at 10^{- 4} and 10^{- 5} dilutions. Both MEMS biosensor and RT-QuIC achieved 100% sensitivity and 100% specificity under the experimental conditions described in this study.

Conclusions: The two immunoassays (CWD Ag-ELISA and TeSeE ELISA) performed comparably on white-tailed deer RPLN samples. MEMS biosensor is a reliable portable tool for CWD diagnosis and RT-QuIC can be used for routine testing of CWD if appropriate testing parameters and interpretive criteria are applied.