Detection and infection dynamics of Marseillevirus-like viruses in Aedes aegypti: Evidence for vertical and human exposure pathways.

Mosquito-specific viruses (MSVs) have garnered increasing interest, particularly those phylogenetically related to arboviruses. Among them, giant viruses of the phylum Nucleocytoviricota, such as Marseillevirus, have been detected in mosquito populations. However, the infection dynamics of these viruses, especially between mosquitoes and vertebrate hosts, remain poorly understood. This study aimed to identify the presence of giant viruses in Aedes aegypti (Ae. aegypti) mosquitoes and to investigate their potential to persist across mosquito generations and infect humans, using Marseilles-like viruses (MLVs) as a model. MLV genomes were detected in all mosquito life stages and in both sexes. Notably, active transcription was observed exclusively in the heads of female mosquitoes. Viral genomes were found in mosquito eggs, indicating vertical transmission. No significant difference in viral load was observed between mosquitoes fed on human versus guinea pig blood. Copies of the viral genome were detected in human blood shortly after a mosquito bite, and although their levels decreased for a short time, they then recovered. Transcriptional activity of MLV genes was detected in human cells both in vivo and in vitro, particularly in association with ingested leukocytes from human blood. This study provides the first evidence for the potential infection of humans with MLV from Ae. aegypti mosquitoes. The likelihood of MLV transmission from susceptible human hosts to mosquitoes appears high, as does the possibility of long-term coexistence of MLV in Aedes mosquitoes with transovarial transmission. In this case, the virus could be transmitted from mosquito to human without replication in mosquitoes, which is more consistent with the definition of mechanical transmission. While active replication in humans was not confirmed, the virus's temporary presence suggests possible interactions, highlighting the need for further research on its ecological and public health implications.