Midgut barriers prevent the replication and dissemination of the yellow fever vaccine inAedes aegypti

Abstract

20 Background 21 To be transmitted to vertebrate hosts via the saliva of their vectors, arthropod-borne viruses have 22 to cross several barriers in the mosquito body, including the midgut infection and escape barriers.23 Yellow fever virus (YFV) belongs to the genus Flavivirus, which includes human viruses transmitted 24 by Aedes mosquitoes, such as Dengue and Zika viruses. The live-attenuated YFV-17D vaccine has 25 been used safely and efficiently on a large scale since the end of World War II. Early studies have 26 shown, using viral titration from salivary glands of infected mosquitoes, that YFV-17D can infect 27 Aedes aegypti midgut, but does not disseminate to other tissues.28 Methodology/Principal Findings 29Here, we re-visited this issue using a panel of techniques, such as RT-qPCR, Western blot, 30 immunofluorescence and titration assays. We showed that YFV-17D replication was not efficient in 31Aedes aegypti midgut, as compared to the clinical isolate YFV-Dakar. Viruses that replicated in the 32 midgut failed to disseminate to secondary organs. When injected into the thorax of mosquitoes, 33 viruses succeeded in replicating into midgut-associated tissues, suggesting that, during natural 34 infection, the block for YFV-17D replication occurs at the basal membrane of the midgut. Our NGS 35 analysis revealed that YFV-Dakar genome exhibited a greater diversity than the vaccine strain; a trait 36 that may contribute to its ability to infect and disseminate efficiently in Ae. aegypti. 37 Conclusions/Significance 38The two barriers associated with Ae. aegypti midgut prevent YFV-17D replication. Our study 39 contributes to our basic understanding of vector-pathogen interactions and may also aid in the 40 development of non-transmissible live virus vaccines.41 42 3 43 Author summary 44 Most flaviviruses, including yellow fever virus (YFV), are transmitted between hosts by mosquito 45 bites. The yellow fever vaccine (YFV-17D) is one of the safest and most effective live virus vaccine 46 ever developed. It is also used as a platform for engineering vaccines against other health-threatening 47 flaviviruses, such as Japanese encephalitis, West Nile, Dengue and Zika viruses. We studied here the 48 replication and dissemination of YFV-17D in mosquitoes. Our data showed that YFV-17D replicates 49 poorly in mosquito midgut and is unable to disseminate to secondary organs, as compare to a YFV 50 clinical isolate. Our study contributes to our basic understanding of the interactions between viruses 51 and their vectors, which is key for conceiving new approaches in inhibiting virus transmission and 52 designing non-transmissible live virus vaccines. 53 54 Introduction 55 Arborviruses, which are transmitted among vertebrate hosts by blood-feeding arthropod vectors, 56 put billions of people at risk worldwide. Viral infection in arthropod is usually persistent. Following 57 uptake of an infectious blood meal by a female mosquito, arbovirus must initiate a productive 58 infection of the midgut epithelium, which consists of a ...