External quality assessment for molecular detection of sand fly-borne phleboviruses circulating in the Mediterranean Basin

Background: Sand fly-borne phleboviruses (SbPV) are globally distributed and pose potential public health risks. Despite increased detection in recent decades, detailed knowledge of their ecology, characteristics and clinical relevance remains limited. Many cases of SbPV infection likely go unreported or misdiagnosed due to limited awareness and the lack of standardized screening. The External Quality Assessment (EQA) reported herein was organized within the framework of the European Union CLIMOS (EU Climate Monitoring and Decision Support Framework for Sand Fly-borne Diseases Detection and Mitigation) project. The aim of this EQA was to standardize the detection of phleboviruses in order to provide comparable data to feed mathematical models for the surveillance of the impact of climate changes and environmental parameters on the kinetics and diversity of sand fly species and on sand fly-borne microorganisms. Methods: Nine laboratories from seven countries participated in the EQA. Each laboratory was provided with eight vials, each containing an anonymous sample; two vials of lyophilized primers and probes to be used for the detection of Toscana virus (TOSV) and several Sandfly fever Sicilian virus (SFSV) species with a reverse-transcriptase PCR (RT-PCR) assay; and one vial of lyophilized primers for the detection of generic phleboviruses with a RT-PCR assay along with the standard operating procedure. The laboratories were instructed to submit their results together with details on the techniques employed. Results: All nine laboratories successfully detected the two TOSV- and the one SFSV-positive samples. Only one laboratory, using a generic phlebovirus assay, detected all of the targeted phleboviruses. Conclusions: All participating laboratories successfully identified the two TOSV and one SFSV using the proposed RT-qPCR assays, albeit with some variations in cycle threshold values across laboratories. The detection rate of SbPV was lower with the generic Phlebovirus assay than with the specific real-time RT-qPCR assays. This EQA aimed to assess the SbPV detection capabilities of molecular tools and strengthen their use, thereby supporting the involvement of laboratories in virus discovery and surveillance beyond their core expertise.