Evaluation of RT-QuIC Diagnostic Performance for Chronic Wasting Disease Detection Using Elk (Cervus canadensis) Ear Punches.

Abstract

Sensitive and specific antemortem diagnostic tests are a prerequisite for effective management of chronic wasting disease (CWD). Paired with readily accessible samples that accurately reflect CWD status, the real-time quaking-induced conversion (RT-QuIC) assay has the potential to enable more effective CWD surveillance and interventions. We evaluated the feasibility of RT-QuIC as a CWD diagnostic test using 6-mm ear tissue biopsies from elk (Cervus canadensis). First, we evaluated the effect of ear spatial location on seeding activity. We observed an effect of ear punch spatial location on the amyloid formation rate (AFR): Samples collected from the periphery of the ear evidenced a statistically significant increase in AFR relative to ear punches from the ventral midline. Gross microdissection of an ear pinna suggested that there was more small nerve innervation around the periphery of the ear. Second, we evaluated the diagnostic sensitivity, specificity, and predictive value of RT-QuIC using ear punches from elk that had been previously diagnosed via ELISA testing. We evaluated the impact of nonstatistical and statistical approaches on diagnostic accuracy. Specificity and positive predictive value were perfect when statistical analyses were used to evaluate the binomial distribution (CWD positive versus CWD negative) of the data. Conversely, sensitivity and negative predictive value were modest, independent of the application of statistical analysis, indicating that RT-QuIC may be susceptible to false-negative data in this context. Taken together, our data support the idea that RT-QuIC, when paired with US Department of Agriculture-approved diagnostic tests, may provide more time to stakeholders for making major management decisions.