Transgenic Aedes aegypti Mosquitoes Transfer Genes into a Natural Population

Abstract

In an attempt to control the mosquito-borne diseases yellow fever, dengue, chikungunya, and Zika fevers, a strain of transgenically modified Aedes aegypti mosquitoes containing a dominant lethal gene has been developed by a commercial company, Oxitec Ltd. If lethality is complete, releasing this strain should only reduce population size and not affect the genetics of the target populations. Approximately 450 thousand males of this strain were released each week for 27 months in Jacobina, Bahia, Brazil. We genotyped the release strain and the target Jacobina population before releases began for >21,000 single nucleotide polymorphisms (SNPs). Genetic sampling from the target population six, 12, and 27–30 months after releases commenced provides clear evidence that portions of the transgenic strain genome have been incorporated into the target population. Evidently, rare viable hybrid offspring between the release strain and the Jacobina population are sufficiently robust to be able to reproduce in nature. The release strain was developed using a strain originally from Cuba, then outcrossed to a Mexican population. Thus, Jacobina Ae. aegypti are now a mix of three populations. It is unclear how this may affect disease transmission or affect other efforts to control these dangerous vectors. These results highlight the importance of having in place a genetic monitoring program during such releases to detect un-anticipated outcomes.

Quantifying Aedes aegypti dispersal in space and time: a modeling approach

“…As a final note, we want to highlight that data from MRR experiments, as the ones considered in this study, do not provide insights into demographic and evolutionary processes in mosquito populations. This information is fundamental to implement and monitor control strategies based on insemination success of released male mosquitoes (Evans et al 2019) and is derived through an array of novel genetics and molecular biology tools applied to genetic mapping, DNA sequencing, or detection of Wolbachia spp. infection (Hemme et al 2010, Schmidt et al 2018.…”

One-step RT-qPCR assay for ZIKV RNA detection in Aedes aegypti samples: A protocol to study infection & gene expression during ZIKV infection

“…At this time, only five studies [19,21,24,43,47] have detected ZIKV RNA in mosquitoes using SYBR green. However, in three of these studies [24,43,47] commercial kits designed to obtain mostly viral RNA from samples were used, which will not allow for analysis of mosquito gene expression from the same sample. In the one study that used a standard extraction kit along with SYBR green did not present any analysis about primers specificity, sensitivity, efficiency or reproducibility [19].…”

“…In recent studies utilizing RT-qPCR to detect ZIKV RNA in mosquitoes, which mostly analyzed vector competence, it is possible to observe a methodological trend favoring the utilization of hydrolysis probes as a fluorescent label (83% of the papers in literature) and the use of viral RNA extraction kits to obtain the RNA templates (56% of the studies). However the number of studies could actually be higher since some of them do not specify the extraction RNA method used for the experiments [9,14,16,18,19,21,22,23,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51]. Although this approach has demonstrated to be relatively effective in detecting ZIKV RNA, since the isolation of viral RNA is prioritized, it does not permit the study of the gene expression in mosquito genes during viral infection using the same samples.…”

Regulation of GM Organisms for Invasive Species Control

“…One crucial aspect of GD is the cargo-the genetic elements that will be dispersed through the population. The recent case of hybridization and introgression of genetic elements from a released transgenic mosquito strain in Brazil (Evans et al, 2019) points to the key elements of ERA: What is the harm and how likely is this to occur? This particular case did not involve a gene drive, but it illustrates a point that would apply to gene drives.…”