Detection of Cell-Fusing Agent virus across ecologically diverse populations of Aedes aegypti on the Caribbean island of Saint Lucia

A tangled threesome: understanding arbovirus infection in Aedes spp. and the effect of the mosquito microbiota

Arboviral infections transmitted by Aedes spp. mosquitoes are a major threat to human health, particularly in tropical regions but are expanding to temperate regions. The ability of Aedes aegypti and Aedes albopictus to transmit multiple arboviruses involves a complex relationship between mosquitoes and the virus, with recent discoveries shedding light on it. Furthermore, this relationship is not solely between mosquitoes and arboviruses, but also involves the mosquito microbiome. Here, we aimed to construct a comprehensive review of the latest information about the arbovirus infection process in A. aegypti and A. albopictus, the source of mosquito microbiota, and its interaction with the arbovirus infection process, in terms of its implications for vectorial competence. First, we summarized studies showing a new mechanism for arbovirus infection at the cellular level, recently described innate immunological pathways, and the mechanism of adaptive response in mosquitoes. Second, we addressed the general sources of the Aedes mosquito microbiota (bacteria, fungi, and viruses) during their life cycle, and the geographical reports of the most common microbiota in adults mosquitoes. How the microbiota interacts directly or indirectly with arbovirus transmission, thereby modifying vectorial competence. We highlight the complexity of this tripartite relationship, influenced by intrinsic and extrinsic conditions at different geographical scales, with many gaps to fill and promising directions for developing strategies to control arbovirus transmission and to gain a better understanding of vectorial competence. The interactions between mosquitoes, arboviruses and their associated microbiota are yet to be investigated in depth.

Vertical and Horizontal Transmission of Cell Fusing Agent Virus in Aedes aegypti

Cell fusing agent virus (CFAV) is an insect-specific flavivirus (ISF) found in Aedes aegypti mosquitoes. ISFs have demonstrated the ability to modulate the infection or transmission of arboviruses such as dengue, West Nile, and Zika viruses. It is thought that vertical transmission is the main route for ISF maintenance in nature. This has been observed with CFAV, but there is evidence of horizontal and venereal transmission in other ISFs. Understanding the route of transmission can inform strategies to spread ISFs to vector populations as a method of controlling pathogenic arboviruses. We crossed individually reared male and female mosquitoes from both a naturally occurring CFAV-positive Ae. aegypti colony and its negative counterpart to provide information on maternal, paternal, and horizontal transmission. RT-PCR was used to detect CFAV in individual female pupal exuviae and was 89% sensitive, but only 42% in male pupal exuviae. This is a possible way to screen individuals for infection without destroying the adults. Female-to-male horizontal transmission was not observed during this study. However, there was a 31% transmission rate from mating pairs of CFAV-positive males to negative female mosquitoes. Maternal vertical transmission was observed with a filial infection rate of 93%. The rate of paternal transmission was 85% when the female remained negative, 61% when the female acquired CFAV horizontally, and 76% overall. Maternal and paternal transmission of CFAV could allow the introduction of this virus into wild Ae. aegypti populations through male or female mosquito releases, and thus provides a potential strategy for ISF-derived arbovirus control. IMPORTANCE Insect-specific flaviviruses (ISFs), are a group of nonpathogenic flaviviruses that only infect insects. ISFs can have a high prevalence in mosquito populations, but their transmission routes are not well understood. The results of this study confirm maternal transmission of cell fusing agent virus (CFAV) and demonstrate that paternal transmission is also highly efficient. Horizontal transmission of CFAV was also observed, aided by evaluation of the pupal infection status before mating with an infected individual. This technique of detecting infection in discarded pupae exuviae has not been evaluated previously and will be a useful tool for others in the field of studying viral transmission in mosquitoes. Identifying these routes of transmission provides information about how CFAV could be maintained in wild populations of mosquitoes and can aid future studies focusing on interactions of CFAV with their hosts and other viruses that infect mosquitoes.