Vector competence of Aedes albopictus for Tonate virus highlights transmission risks in temperate and tropical regions.

Recent evidence of vertical transmission of Tonate virus (TONV) during early pregnancy and its association with fetal neurological anomalies highlights its potential public health threat. TONV is an understudied alphavirus endemic to French Guiana. The growing presence of Aedes (Ae.) albopictus in Europe raises concerns about its ability to transmit emerging arboviruses, including TONV. We assessed the vector competence of Ae. albopictus populations from mainland France and La Réunion Island via oral infections using different TONV doses. Both populations supported efficient viral replication, with infectious viral particles appearing in saliva by day 5 post-infection. Infection rate (IR), stepwise dissemination rate (sDR), and transmission efficiency (TE) increased with rising viral concentrations. At a viral concentration of 10(6) PFU/mL IR reached 80%, and TE at day 5 post-infection was 27% for the mainland strain and 37% for the La Réunion strain. Notably, TE declined over time in the mainland strain, while increasing progressively in the La Réunion population. Comparative infections with Chikungunya virus revealed that TONV was transmitted at similar or greater rates, confirming Ae. albopictus as a competent vector. Sequencing of mosquito organs revealed intra-host TONV genetic variability. A recurrent polymorphism at position 11,357 in the 3'UTR was detected in body tissues but not in heads of La Réunion mosquitoes, suggesting tissue-specific selection or bottlenecks. Our results demonstrate that Ae. albopictus from both tropical and temperate areas can efficiently transmit TONV and emphasize the importance of genomic surveillance to anticipate risk of its emergence in areas where this vector is established.