TaqMan Multiplex Real-time PCR Assay for Crimean-Congo Hemorrhagic Fever Virus Diagnosis Using Armored RNA Technology

Crimean-Congo hemorrhagic fever virus (CCHFV) is a highly lethal virus that causes hemorrhagic fever inhumansand is endemic inmanycountries, including Iran. Therefore, fast, accurate, and reliable diagnosis is crucial for patient management and outbreak control.

This study aims to optimize a TaqMan multiplex real-time RT-PCR for the rapid and specific diagnosis of CCHFV.

In this study, the L (NC_005301.3) and S (NC_005302.1) fragments were used as reference sequences for blast analysis. The L and S sequence segments of CCHFV with more than 90% identity from different areas were downloaded from the Genbank database. Primers and probes were designed based on the best-conserved regions of CCHFV L and S sequence segments. To construct the plasmid, a 1751 bp fragment from the MS2 phage that was previously amplified using cloning primers was inserted into the pET-32a plasmid. The S and L segments of the CCHFV, which were 110 bp and 135 bp, respectively, were inserted downstream of the MS2 phage sequence from HindIII to NotI. The Viral-like particles (VLPs) were produced in Escherichia coli, strain BL-21(DE3), in the presence of 1 mM Isopropyl -D-1-thiogalactopyranoside (IPTG). The stability of VLP particles was confirmed in the presence of the ribonuclease enzyme. The fabrication of VLPs was approved by transmission electron microscopy (TEM) with negative staining (1% phosphotungstic acid). To validate the specificity of the primers and probes sequences, we compared them to the NCBI database and tested them experimentally using extracted DNA and RNA samples from healthy subjects and an infectious panel.

The VLPs showed complete resistance in the presence of the ribonuclease enzyme, and the TEM results confirmed that the VLPs were correctly produced. The TaqMan multiplex real-time RT-PCR confirmed that the primers and probes were designed correctly and were completely specific to the CCHFV. The limit of detection (LOD) of the multiplex assay for the L and S genes was one copy of the VLPs per L.

This TaqMan assay is reliable for amplifying CCHFV due to its design on conserved regions of the CCHFV sequences, which have minimal variability and high specificity.