Modelling the ecological dynamics of mosquito populations with multiple co-circulating Wolbachia strains

Abstract

Wolbachia intracellular bacteria successfully reduce the transmissibility of arthropod-borne viruses (arboviruses) when introduced into virus-carrying vectors such as mosquitoes. Despite the progress made by introducing Wolbachia bacteria into the Aedes aegypti wild-type population to control arboviral infections, reports suggest that heat-induced loss-of-Wolbachia-infection as a result of climate change may reverse these gains. Novel, supplemental Wolbachia strains that are more resilient to increased temperatures may circumvent these concerns, and could potentially act synergistically with existing variants. In this article, we model the ecological dynamics among three distinct mosquito (sub)populations: a wild-type population free of any Wolbachia infection; an invading population infected with a particular Wolbachia strain; and a second invading population infected with a distinct Wolbachia strain from that of the first invader. We explore how the range of possible characteristics of each Wolbachia strain impacts mosquito prevalence. Further, we analyse the differential system governing the mosquito populations and the Wolbachia infection dynamics by computing the full set of basic and invasive reproduction numbers and use these to establish stability of identified equilibria. Our results show that releasing mosquitoes with two different strains of Wolbachia did not increase their prevalence, compared with a single-strain Wolbachia-infected mosquito introduction and only delayed Wolbachia dominance.

Quantifying the impact of Wolbachia releases on dengue infection in Townsville, Australia

“…The pathogen development rates (i.e., the rate at which dengue-exposed Wolbachia -infected ( ) and uninfected ( ) mosquitoes become actively infectious) and maturation rates for both Wolbachia -infected ( ) and uninfected ( ) mosquitoes are assumed to be the same, i.e., and . Further, the cytoplasmic incompatibility (CI), which describes the mating pair of uninfected female and Wolbachia -infected male mosquitoes inability to produce viable offspring and the imperfect maternal transmission of Wolbachia infection from Wolbachia -infected female mosquito to offspring as described in 36 , 37 were also incorporated in the model.…”

“…To do so, we model both the human dengue transmission dynamics alongside the mosquito population dynamics in the presence of Wolbachia infection. Other models have described the ecological dynamics of the Wolbachia -infected mosquito population only 36 , 37 and both Wolbachia and dengue dynamics in humans concurrently 33 , 34 . Here, we extend the Wolbachia -mosquito models in 36 , 37 via incorporating human populations and dengue infection dynamics, and extend models 33 , 34 to include the locally-acquired and imported dengue cases’ compartments to quantify the impact of Wolbachia releases on dengue infection in Townsville.…”

“…Other models have described the ecological dynamics of the Wolbachia -infected mosquito population only 36 , 37 and both Wolbachia and dengue dynamics in humans concurrently 33 , 34 . Here, we extend the Wolbachia -mosquito models in 36 , 37 via incorporating human populations and dengue infection dynamics, and extend models 33 , 34 to include the locally-acquired and imported dengue cases’ compartments to quantify the impact of Wolbachia releases on dengue infection in Townsville. Our model estimates the dengue transmission probabilities per mosquito bite between humans and non- Wolbachia , and Wolbachia- infected mosquitoes and in turn provides insight on the impact of Wolbachia introduction on dengue incidence.…”

MixedWolbachiainfections resolve rapidly duringin vitroevolution

“…The quick and reproducible competitive exclusion of w Ri by w Mel in two D. melanogaster cell types across a range of starting frequencies suggests that mixed infections resolve reliably and quickly, consistent with theoretical predictions [25] . This potentially explains why unstable mixed infections (opposed to stable superinfections) are rarely observed in nature [17][18][19] . The selection coefficients estimated for w Mel demonstrate a strong relative fitness compared to w Ri across both D. melanogaster cell lines.…”

“…A major challenge involves parameterizing the infrequent, but vital events in the process. Based upon the low rates of mixed infections in infected hosts and the novel infections in uninfected hosts [17][18][19] , joint rates of horizontal transmission and successful proliferation in a new host are exceedingly low. However, it is unclear whether both rates are low, or if horizontal transmission rates are high, but exceedingly few bacteria persist and colonize host tissues.…”