Sand flies and Toscana virus: intra-vector infection dynamics and impact on Phlebotomus perniciosus life-history traits

Toscana virus (TOSV) is a leading cause of summer viral meningitis in central Italy and south of France, and can cause severe neurological cases. Within the Mediterranean basin, it is transmitted by hematophagous sand flies belonging to the Phlebotomus genus. Despite the identification of the primary TOSV vectors, the viruss developmental cycle in vector species remains largely unknown. Limited research has been conducted on transmission dynamics and the vectorial competence and capacity of the principal TOSV vector, Phlebotomus perniciosus. In this context, we investigated the intra-vector TOSV infection dynamics in Ph. perniciosus, as well as its impact on the vectors life history traits. Female sand flies were experimentally infected with TOSV though an artificial blood meal. Systemic dissemination of the virus was observed approximately three days post-infection, potentially resulting in a shorter extrinsic incubation period. Moreover, the study revealed a longer hatching time for eggs laid by infected females. This research not only confirmed the vector competence of Ph. perniciosus but also provided the first insight into TOSVs developmental cycle and its impact on the vector. These findings prompt further exploration of TOSV transmission dynamics, raise new hypotheses on the virus transmission and highlight the importance of follow-up studies. Author summaryToscana virus (TOSV) is a reemerging sandfly-borne virus causing neuroinvasive infections in humans. This virus is endemic in the Mediterranean basin, with a potential risk of introduction in northern Europe and Asia. Despite decades of research, few studies have focused on the development cycle of TOSV in sand flies and the dynamics of transmission. Here, we provide a comprehensive study of the intra-vector dynamics of TOSV infection and its impact on both vector biology and transmission. Through experimental infections of the major vector Phlebotomus perniciosus, we not only confirmed vector competence but also provided the first insight into the TOSV developmental cycle in the vector by estimating the extrinsic incubation period at six days. Our study reveals an impact of TOSV infection on vector hatching time leading to a delayed emergence of infected sand flies, with a potential impact on transmission. Our findings encourage further exploration of transmission dynamics, raise new hypotheses on alternative transmission pathways, and emphasize the importance of follow-up studies.