Comparison of the detection of the chronic wasting disease prion by real-time quaking-induced conversion (rtQuIC) and silica nanoparticle-rtQuIC (nano-rtQuIC) assays in retropharyngeal lymph nodes of white-tailed deer, mule deer, and Rocky Mountain elk.

Chronic wasting disease (CWD) continues to be detected across the United States and globally; enhanced detection is critical for disease management. Silica nanoparticles (SiNPs) have shown promise in reducing time-to-detection for the real-time quaking-induced conversion (rtQuIC) assay in white-tailed deer (WTD) retropharyngeal lymph nodes (RPLNs). We aimed to document such decreased time-to-detection in 3 Wyoming, USA, cervid species. Additionally, we investigated maximum slope (max slope) as a metric of differentiating CWD status by rtQuIC testing, and how the receiver operating characteristic (ROC) may be useful for setting thresholds for QuIC outcomes. We performed rtQuIC testing, with and without SiNPs, on postmortem RPLNs from 39 WTD (Odocoileus virginianus), 40 mule deer (O. hemionus), and 40 Rocky Mountain elk (Cervus canadensis nelsoni). To measure effects of using SiNPs in the rtQuIC assay (nano-rtQuIC), median time-to-thresholds (tTh) for each sample replicate from QuIC and nano-rtQuIC was obtained using ROC thresholds. We found that nano-rtQuIC decreased the median tTh by 4.9, 5.3, and 3.6 h in WTD, mule deer, and elk, respectively. When using nano-rtQuIC, test sensitivity decreased by 5% in elk and by 4.8% in mule deer RPLN samples, whereas test sensitivity increased in WTD from 83.3% to 95.2%, indicating inhibition under the 50°C rtQuIC condition for WTD. Mechanisms of inhibition of rtQuIC by WTD RPLNs, comparatively by species, are unknown, but SiNPs and max slope analysis helped optimize rtQuIC test results. Interlaboratory validation and testing in a broader range of biological cervid samples would be useful for confirming these initial findings.