Antigenic and biological characterization of Toscana virus, a new Phlebotomus fever group virus isolated in Italy

Toscana (TOS) virus, a new member of the Phlebotomus fever serogroup of arboviruses, was isolated from sandflies collected in Italy. It was shown to be closely related to Sandfly fever Naples (SFN) virus. The antigenic relationships between the two viruses were analysed in the complement fixation (CF), plaque reduction neutralization (PRN) and indirect fluorescent antibody (IFA) tests. TOS virus multiplied to high titres with a cytopathic effect (CPE) in several vertebrate cell cultures (e.g. Vero, BHK-21, etc.), whereas it failed to replicate in mosquito cell cultures. Plaque formation by TOS virus in Vero cells was not affected by incorporating dimethyl sulphoxide in the overlay, which is known to enhance plaque formation by SFN virus. Some biological characteristics in cell cultures and in mice of a mouse-adapted and a cell-adapted TOS virus strain were studied. After 4-6 passages in the two different systems, changes in plaque size, in the amount of autointerfering activity and of virulence for mice were observed.