From Lab to Field: The Influence of Urban Landscapes on the Invasive Potential of Wolbachia in Brazilian Aedes aegypti Mosquitoes

Abstract

BackgroundThe symbiotic bacterium Wolbachia is currently being trialled as a biocontrol agent in several countries to reduce dengue transmission. Wolbachia can invade and spread to infect all individuals within wild mosquito populations, but requires a high rate of maternal transmission, strong cytoplasmic incompatibility and low fitness costs in the host in order to do so. Additionally, extensive differences in climate, field-release protocols, urbanization level and human density amongst the sites where this bacterium has been deployed have limited comparison and analysis of Wolbachia’s invasive potential.Methodology/Principal FindingsWe examined key phenotypic effects of the wMel Wolbachia strain in laboratory Aedes aegypti mosquitoes with a Brazilian genetic background to characterize its invasive potential. We show that the wMel strain causes strong cytoplasmic incompatibility, a high rate of maternal transmission and has no evident detrimental effect on host fecundity or fertility. Next, to understand the effects of different urban landscapes on the likelihood of mosquito survival, we performed mark-release-recapture experiments using Wolbachia-uninfected Brazilian mosquitoes in two areas of Rio de Janeiro where Wolbachia will be deployed in the future. We characterized the mosquito populations in relation to the socio-demographic conditions at these sites, and at three other future release areas. We then constructed mathematical models using both the laboratory and field data, and used these to describe the influence of urban environmental conditions on the likelihood that the Wolbachia infection frequency could reach 100% following mosquito release. We predict successful invasion at all five field sites, however the conditions by which this occurs vary greatly between sites, and are strongly influenced by the size of the local mosquito population.Conclusions/SignificanceThrough analysis of laboratory, field and mathematical data, we show that the wMel strain of Wolbachia possesses the characteristics required to spread effectively in different urban socio-demographic environments in Rio de Janeiro, including those where mosquito releases from the Eliminate Dengue Program will take place.

Diet-Induced Nutritional Stress and Pathogen Interference in Wolbachia-Infected Aedes aegypti

“…The issue of nutritional stress and pathogen interference is particularly important in the field where mosquitoes are released in locations with complex environmental and nutritional factors, and high levels of endemic dengue transmission [50, 112]. Adult Ae .…”

“…The w Mel infection was introgressed into a Brazilian genetic background by breeding infected females with uninfected, field-collected males over nine generations, as previously described [112]. A subset of these mosquitoes were treated with tetracycline to clear the Wolbachia infection and then had their gut microbiota recolonised by introducing larval water from untreated mosquitoes into rearing trays, as previously described, with this line serving as a Wolbachia -uninfected control line (Tet) [112]. 50 wildtype, Wolbachia -uninfected F 1 -F 2 males were introduced into colony cages for both w Mel and Tet lines each generation, in order to limit the occurrence of inbreeding and genetic divergence between the lines.…”

Zika virus: a new pandemic threat

“…Once infected, the mosquitoes do not pick up and transmit viruses as easily. Wolbachia bacteria are transmitted to the next generation through eggs and can be sustained in the environment for a long time [46,47]. However, some concerns remain that using these genetically modified mosquito vectors may cause unintended, negative effects to the ecosystem.…”

Analysis of the vectorial capacity of vector-borne diseases using moment-generating functions

“…For instance, the distribution of mosquitoes per human can vary widely across various localities as shown in [23] .…”