TOSCANA VIRUS: EMERGING OR UNDERVALUED VIRUS?

Objective Toscana Virus (TOSV) belongs to the Phlebovirus genus of the Bunyaviridae family; it is an arthropodborne virus transmitted to humans by Phlebotomus, Sergentomyia and Lutzomya genera, and could cause aseptic meningitis and meningoencephalitis. Its genome is composed of three negative singlestrand RNA segments designated Large, Medium, and Small. TOSV represents an important emerging pathogen and its presence is being investigated in several European countries around the Mediterranean basin. The aim of this retrospective study was to assess and estimate the current active circulation of TOSV in patients with encephalitis and/or meningoencephalitis of unknown etiology. Methods Ninety cerebrospinal fluid samples (CSF) were tested. They were collected between April 2012 and November 2013 from patients living in Eastern Sicily (Italy), who were affected by encephalitis or meningoencephalitis of unknown etiology. The mean age of the patients was 38 years (range 2 months to 87 years); the majority of them were white (90.7%) males (60.5%). All samples were stored at -20°C. The RNA extraction was performed by a NucliSens® easyMAG® system (bioMérieux SA, Marcy l'Etoile, France). The reverse transcription and the detection of TOSV cDNA were performed respectively by Alert PCR RT-Kit plus and TOSCANA VIRUS oligomix Alert Kit (ELITech Group S.p.A., Paris, France). Results All of the samples were originally screened for the most common neurotropic viruses, including enterovirus and herpes simplex viruses, and were negative. TOSV RNA was detected in five (5.5%) of the samples tested. All positive patients were native of Eastern Sicily and had not travelled in the 6 months before the onset of symptoms. Three of them were aged between 12 and 14 years and were symptomatic in late spring or in early autumn 2013; the other two patients were 52 and 64 years old and were symptomatic during summer 2013. Conclusions In the geographical areas where TOSV is endemic, it represents one of the three most prevalent viruses that cause meningitis during warm seasons. The study and surveillance of Phlebovirus infections should be considered worldwide, since they might cause emergent diseases and could represent an important public health problem in the future. In Central Italy, TOSV accounted for the first cause of CNS infections during warm seasons, with an incidence of 30-52%. TOSV was also isolated in other regions of Italy such as Piedmont, Sardinia, Sicily, and Umbria. Even if our area is a natural habitat of Phlebotomus, the incidence of TOSV is lower than other endemic regions. Further research is needed to establish if the results are undervalued due to a lack of viral research in the presence of neurological manifestations or the virus really does not circulate in Eastern Sicily. Finally, TOSV remains a neglected human pathogen that will merit further investigations to understand it better.