Evidence of Toscana virus infections without central nervous system involvement: a serological study

In central Italy, acute lymphocytic meningitis and meningoencephalitis due to a Phlebotomus transmitted virus (Phlebovirus Toscana, TOSv) occurring throughout the summer are frequently observed. Several serum specimens of patients hospitalized with a clinical picture of viral meningitis/meningoencephalitis showed anti TOS-IgG reactivity suggestive of a previous infection occurring at an unknown time in the past. This observation led us to design a serological investigation of 83 household contacts of 46 summertime CNS infection patients (index cases) with the purpose of evaluating the percentage of both IgG and IgM in seropositive healthy individuals, living, like the index cases, in areas at high risk of phlebotomine sandfly bites. The serological study was carried out using an ELISA method: 22% of the sera showed a reactivity for anti-TOS IgG antibodies and 6% resulted IgG/IgM positive; none of them reported having had any symptoms of CNS involvement; the distribution of seropositive cases was similar in contacts of both TOS-confirmed and TOS-negative cases. Our results indicate: (1) that phlebovirus Toscana is frequently implicated in cases with CNS disease as well as in infections occurring without neurological involvement; (2) in our country the ecological requirements encompass the conditions in and around the human settlements for phlebotomine sandflies to become peridomestic thus amplifying the risk of TOSv infections, which are in fact widespread and frequent in Siena and its surroundings.