Detection of human orthopoxvirus infections and differentiation of smallpox virus with real-time PCR.

We developed a real-time PCR protocol to detect orthopoxviruses (OPVs) from different clinical specimens and to separate variola virus from other OPVs. In our protocol, we used automated nucleic acid extraction system together with real-time PCR to create a simple, safe and fast procedure to obtain an initial result. The sensitivity was better by using designed hybridization probes as compared to SYBR green I for detection. The detection limit ranged from 13 to 1,300 copies per 20 microl reaction volume depending on the sample type. The PCR detected all OPVs pathogenic to human (variola, cowpox, monkeypox, vaccinia) as well as camelpox and ectromelia viruses. Amplification of variola virus sequences could be distinguished from other OPVs by melting curve analysis. We also demonstrated the applicability of the assay in human cases of cowpox and vaccinia virus infections.