Natural and engineered mosquito immunity

Abstract

A recent paper in BMC Microbiology shows how suppression of mosquito innate immunity against a virus that the mosquito can normally tolerate increases mosquito mortality. This is just one of several approaches that may soon bring genetics-based mosquito control methods from the laboratory into the field.

Figure 1

Targeted RNA interference against dengue virus infection. Self-complementary RNA with sequences from dengue virus is expressed from a promoter that expresses in the gut of the mosquito soon after a blood meal [5]. This RNA folds into a hairpin conformation with an extended double-stranded region. This double-stranded RNA is cut into 20–25 bp fragments by Dicer. These fragments are bound by the RISC complex of proteins and one strand is removed. The RISC complex is now primed to bind and cleave target sequences from an infecting dengue virus, preventing translation from the RNA and replication of the virus.

Figure 2

Population replacement and population suppression. (a) In population replacement strategies, the wild population is invaded by a heritable modification (e.g. transgene [5,9] or pathogenic Wolbachia [8]) that reduces the vector competence of the mosquitoes that carry it. The number of competent vectors therefore declines, but the total number of (female) mosquitoes remains relatively constant, though possibly with some transient change during the invasion. (b) In contrast, a population suppression strategy aims to reduce the total number of vector mosquitoes. The two panels illustrate the changes in female population number and type over time for the two strategies. In both cases the situation will eventually reverse due to various pressures such as resistance, mutation, immigration, etc, unless some maintenance activities are undertaken.