Characterisation of the antiviral RNA interference response to Toscana virus in sand fly cells

Abstract

Toscana virus (TOSV) (Bunyavirales, Phenuiviridae, Phlebovirus, Toscana phlebovirus) and other related human pathogenic arboviruses are transmitted by phlebotomine sand flies. TOSV has been reported in nations bordering the Mediterranean Sea among other regions. Infection can result in febrile illness as well as meningitis and encephalitis. Understanding vector-arbovirus interactions is crucial to improving our knowledge of how arboviruses spread, and in this context, immune responses that control viral replication play a significant role. Extensive research has been conducted on mosquito vector immunity against arboviruses, with RNA interference (RNAi) and specifically the exogenous siRNA (exo-siRNA) pathway playing a critical role. However, the antiviral immunity of phlebotomine sand flies is less well understood. Here we were able to show that the exo-siRNA pathway is active in a Phlebotomus papatasi-derived cell line. Following TOSV infection, distinctive 21 nucleotide virus-derived small interfering RNAs (vsiRNAs) were detected. We also identified the exo-siRNA effector Ago2 in this cell line, and silencing its expression rendered the exo-siRNA pathway largely inactive. Thus, our data show that this pathway is active as an antiviral response against a sand fly transmitted bunyavirus, TOSV. Author summaryToscana virus (TOSV) is a bunyavirus that is transmitted to humans through the bite of phlebotomine sand flies. Examining the immune responses that control arboviruses in their vectors is critical for understanding how these organisms control infection, as this may affect transmission. The exogenous siRNA (exo-siRNA) pathway is a critical antiviral immune response in mosquitoes, but much less is known about the pathway in sand flies. Here we show that a functional exo-siRNA pathway exists in a sand fly-derived cell line and that it is active as a response to TOSV infection. These findings improve our understanding of antiviral immunity in vectors in general, and phlebotomine sand flies in particular.