Evaluation of the Tetracore Orthopox BioThreat® antigen detection assay using laboratory grown orthopoxviruses and rash illness clinical specimens

Abstract

The commercially available Orthopox BioThreat® Alert assay for orthopoxvirus (OPV) detection is piloted. This antibody-based lateral-flow assay labels and captures OPV viral agents to detect their presence. Serial dilutions of cultured Vaccinia virus (VACV) and Monkeypox virus (MPXV) were used to evaluate the sensitivity of the Tetracore assay by visual and quantitative determinations; specificity was assessed using a small but diverse set of diagnostically relevant blinded samples from viral lesions submitted for routine OPV diagnostic testing. The BioThreat® Alert assay reproducibly detected samples at concentrations of 10(7)pfu/ml for VACV and MPXV and positively identified samples containing 10(6)pfu/ml in 4 of 7 independent experiments. The assay correctly identified 9 of 11 OPV clinical samples and had only one false positive when testing 11 non-OPV samples. Results suggest applicability for use of the BioThreat® Alert assay as a rapid screening assay and point of care diagnosis for suspect human monkeypox cases.

Fig. 1

Tetracore Orthopox cassette image and strip layout showing application port, the sample test line for the orthopox detection, and a control line to indicate the test was successfully completed.

Fig. 2

Sensitivity of BioThreat Alert reader scanned strips to (a) lab grown vaccinia virus and (b) negative controls. The manufacturer cutoff for the reader was 0.01. Samples were applied in duplicate to test strips and measured at approximately 7.5 min intervals. Not all samples had measurements taken at each interval.