Vector bionomics and vectorial capacity as emergent properties of mosquito behaviors and ecology

Abstract

<jats:title>Abstract</jats:title><jats:p>Mosquitoes are important vectors for pathogens of humans and other vertebrate animals. Some aspects of adult mosquito behavior and mosquito ecology play an important role in determining the capacity of vector populations to transmit pathogens. Here, we re-examine factors affecting the transmission of pathogens by mosquitoes using a new approach. Unlike most previous models, this framework considers the behavioral states and state transitions of adult mosquitoes through a sequence of activity bouts. We developed a new framework for individual-based simulation models called MBITES (Mosquito Bout-based and Individual-based Transmission Ecology Simulator). In MBITES, it is possible to build models that simulate the behavior and ecology of adult mosquitoes in exquisite detail on complex resource landscapes generated by spatial point processes. We also developed an ordinary differential equation model which is the Kolmogorov forward equations for models developed in MBITES under a specific set of simplifying assumptions. While infection of the mosquito and pathogen development are one possible part of a mosquito’s state, that is not the main focus. Using extensive simulation using some models developed in MBITES, we show that vectorial capacity can be understood as an emergent property of simple behavioral algorithms interacting with complex resource landscapes, and that relative density or sparsity of resources and the need to search can have profound consequences for mosquito populations’ capacity to transmit pathogens.</jats:p>

Evaluating insecticide resistance across African districts to aid malaria control decisions

“…The relative abundance of these vectors has been mapped across Africa by a previous study, which showed that insecticide-treated net and IRS use affect the relative abundance of these species ( 35 ). Variation in the behavior of these vectors also influences how likely it is that they come into contact with indoors, insecticide-based interventions and, ideally, this variable should also be considered alongside insecticide resistance ( 36 – 39 ).…”

A New Test of a Theory about Old Mosquitoes

“…In practice, mosquito population densities are rarely measured directly, but the number of mosquitoes per human is assumed to be directly proportional to the human-biting rate (HBR) (defined as the number of bites, per person, per day). Recently, several new mathematical models of adult behaviors and ecology have been developed to estimate the effect sizes of vector control on malaria transmission [6][7][8][9]. Some of these new models consider complex feedbacks and population dynamic thresholds that Macdonald's analysis ignored and they show that vector control could have large, nonlinear effects on mosquito population densities [5,10].…”

“…With that in mind, we consider the evolution of formulas for VC and extensions of it as cases of a single motivating concept: VC is defined to be the number of infective bites arising from all the mosquitoes biting a single human on a single day, as if the human was perfectly infectious. If appropriate, VC could thus be computed as an expectation for each individual on any day [9].…”

“…The concept of VC and the formulas remains useful as a way of understanding vector control, even if the models are capable of predicting changes in the EIR and malaria outcomes. The VC can be computed numerically, either by directly computing the number of infective bites that would arise from a human on a single day if it were perfectly infectious, or by computing the average values of the statistics that comprise VC and taking their product [9]. VC and its formulas are a useful way of comparing models, making predictions about changes in the parameters that can be measured and tested, and fitting models to data.…”

Community-level impacts of spatial repellents for control of diseases vectored by Aedes aegypti mosquitoes

“…The relative probability of transmission following partial and full blood feeding is unclear, but increased partial blood feeding could negatively affect the epidemiological impact of the product if the probability of transmission is similar to what it is with full blood feeding [25]. Conversely, an increase in number of feeds could be accompanied with increased mortality due to the risks involved with blood feeding, which would further enhance the impact of the SR [26][27][28]. How such hazards differ in response to product exposure remains to be investigated.…”