Toscana virus inhibits the interferon beta response in cell cultures.

Toscana virus (TOSV) is an emerging pathogen in the Mediterranean basin where it causes summertime outbreaks of aseptic meningitis and meningoencephalitis. Many aspects of TOSV biology remain unknown including the possible implication of an amplifying mammalian host besides its vector. The three experiments described here were designed to assess the relationship between TOSV and type-I interferon (IFN) response. The main findings were as follows. First, TOSV growth in Vero cells is sensitive to an antiviral state induced by low-dose addition of exogenous IFN beta (IFN-β) (10IU/ml). Second, no IFN-β mRNA or IFN-β was detectable after infection of HeLa and 293T cells by TOSV. Finally, TOSV inhibits IFN-β production induced by Sendaï virus, a well known inducer of IFN-β production. In addition to showing that TOSV can inhibit the IFN-β response, these findings suggest that anti-IFN capability is maintained by regular contact with that of a mammalian host.