Human behaviors: A threat to mosquito control?

Impact of regional climate change on the mosquito vector Aedes albopictus in a tropical island environment: La Réunion

The recent expansion of Aedes albopictus across continents in both tropical and temperate regions and the exponential growth of dengue cases over the past 50 years represent a significant risk to human health. Although climate change is not the only factor responsible for the increase and spread of dengue cases worldwide, it might increase the risk of disease transmission at global and regional scale. Here we show that regional and local variations in climate can induce differential impacts on the abundance of Ae. albopictus. We use the instructive example of Réunion Island with its varied climatic and environmental conditions and benefiting from the availability of meteorological, climatic, entomological and epidemiological data. Temperature and precipitation data based on regional climate model simulations (3 km × 3 km) are used as inputs to a mosquito population model for three different climate emission scenarios. Our objective is to study the impact of climate change on the life cycle dynamics of Ae. albopictus in the 2070-2100 time horizon. Our results show the joint influence of temperature and precipitation on Ae. albopictus abundance as a function of elevation and geographical subregion. At low-elevations areas, decreasing precipitation is expected to have a negative impact on environmental carrying capacity and, consequently, on Ae. albopictus abundance. At mid- and high-elevations, decreasing precipitation is expected to be counterbalanced by a significant warming, leading to faster development rates at all life stages, and consequently increasing the abundance of this important dengue vector in 2070-2100.

An almost periodic model to describe phenology mismatches in mutualistic interactions

We study seasonal mutualistic interactions between two species. The model takes into account the climate-mediated shifts that can change the phenologies of mutualistic species. We show conditions on the parameters of the model that guarantee global stability. Numerical simulations are performed for different scenarios associated with seasonal changes. They show that if periodic time-dependence is used to approximate an almost periodic one, then not only the densities of the mutualistic populations but also the overlapping intervals describing the interval of co-occurrence can be either underestimated or overestimated. Therefore, using an almost periodic model can be more adequate to design conservation strategies for asynchronous phenology.

Sterile insect technique with accidental releases of sterile females. Impact on mosquito-borne diseases control when viruses are circulating

The sterile insect technique (SIT) is a technique to control some vectors of diseases by releasing sterile males. However, during these releases, sterilized females can be (accidentally) released and since only females are vectors of diseases, it is important to study their impact when arthropod viruses are circulating. To that aim, we develop and study an entomological-epidemiological model, considering either permanent or periodic releases. Qualitative analyses of the continuous and periodic models are conducted. We highlight a critical sterile males release rate, Λ_M^crit, above which the control of wild population is always effective, using massive releases. Estimating the basic reproduction number of the epidemiological model, R₀², we show that if it is above a certain threshold, R_0,∗², that depends on the basic offspring number, N, and the release rate of sterile females, the epidemiological risk can only be controlled using (very) massive releases. Otherwise, we can estimate the basic reproduction number of the SIT epidemiological model, R_0,SIT², that shapes the stability property of the (periodic) disease-free equilibrium. We show that it might be possible to take R_0,SIT² below 1 using non-massive, but large enough, releases. However, practically, it seems more efficient to consider massive releases, followed by small releases once the vector population is small enough. In addition to SIT, we also recommend mechanical control, i.e. the reduction of breeding sites, that greatly improves the efficacy of SIT, in terms of duration or size of the releases. Our results reveal that outside an epidemic period, the release of sterile females is not an issue, as long as the sterile males release rate is greater than Λ_M^crit. Within an epidemic period, we show that sterile females releases do not really impact the SIT efficiency, as long as the release rate, Λ_F, is lower than a critical value, Λ_F^crit, that depends on the mosquito and epidemiological threshold parameters, N, and R₀². To illustrate numerically our theoretical results, we consider Dengue parameters. We estimate all thresholds and also the effective reproduction number, R_eff², and highlight the importance of early permanent or periodic SIT control to prevent or mitigate the risk of a Dengue epidemic, with and without sterile females releases.

Sterile Insect Technique (SIT) against Aedes Species Mosquitoes: A Roadmap and Good Practice Framework for Designing, Implementing and Evaluating Pilot Field Trials

Aedes albopictus and Aedes aegypti are invasive mosquito species that impose a substantial risk to human health. To control the abundance and spread of these arboviral pathogen vectors, the sterile insect technique (SIT) is emerging as a powerful complement to most commonly-used approaches, in part, because this technique is ecologically benign, specific, and non-persistent in the environment if releases are stopped. Because SIT and other similar vector control strategies are becoming of increasing interest to many countries, we offer here a pragmatic and accessible 'roadmap' for the pre-pilot and pilot phases to guide any interested party. This will support stakeholders, non-specialist scientists, implementers, and decision-makers. Applying these concepts will ensure, given adequate resources, a sound basis for local field trialing and for developing experience with the technique in readiness for potential operational deployment. This synthesis is based on the available literature, in addition to the experience and current knowledge of the expert contributing authors in this field. We describe a typical path to successful pilot testing, with the four concurrent development streams of Laboratory, Field, Stakeholder Relations, and the Business and Compliance Case. We provide a graphic framework with criteria that must be met in order to proceed.

A mathematical model of cholera in a periodic environment with control actions

In this paper, we studied the impact of sensitization and sanitation as possible control actions to curtail the spread of cholera epidemic within a human community. Firstly, we combined a model of Vibrio Cholerae with a generic SIRS cholera model. Classical control strategies in terms of the sensitization of population and sanitation are integrated through the impulsive differential equations. Then we presented the theoretical analysis of the model. More precisely, we computed the disease free equilibrium. We derive the basic reproduction number [Formula: see text] which determines the extinction and the persistence of the infection. We show that the trivial disease-free equilibrium is globally asymptotically stable whenever [Formula: see text], while when [Formula: see text], the trivial disease-free equilibrium is unstable and there exists a unique endemic equilibrium point which is globally asymptotically stable. Theoretical results are supported by numerical simulations, which further suggest that the control of cholera should consider both sensitization and sanitation, with a strong focus on the latter.

Complementarity of empirical and process-based approaches to modelling mosquito population dynamics with Aedes albopictus as an example-Application to the development of an operational mapping tool of vector populations

Mosquitoes are responsible for the transmission of major pathogens worldwide. Modelling their population dynamics and mapping their distribution can contribute effectively to disease surveillance and control systems. Two main approaches are classically used to understand and predict mosquito abundance in space and time, namely empirical (or statistical) and process-based models. In this work, we used both approaches to model the population dynamics in Reunion Island of the 'Tiger mosquito', Aedes albopictus, a vector of dengue and chikungunya viruses, using rainfall and temperature data. We aimed to i) evaluate and compare the two types of models, and ii) develop an operational tool that could be used by public health authorities and vector control services. Our results showed that Ae. albopictus dynamics in Reunion Island are driven by both rainfall and temperature with a non-linear relationship. The predictions of the two approaches were consistent with the observed abundances of Ae. albopictus aquatic stages. An operational tool with a user-friendly interface was developed, allowing the creation of maps of Ae. albopictus densities over the whole territory using meteorological data collected from a network of weather stations. It is now routinely used by the services in charge of vector control in Reunion Island.

Evaluation of Barrier Sprays for Controlling Mosquitoes in Eastern North Carolina: Can Land Cover and Spatial Analyses Improve Predictions of Efficacy?

Mosquitoes can be a nuisance and can transmit pathogens causing numerous diseases. Homeowners may hire private companies that use barrier sprays to alleviate mosquito-related issues, especially in areas where government funding for mosquito control programs is limited. Here, the spatial distribution of mosquitoes was evaluated in a suburban neighborhood during successive treatments with either Bifen Insecticide/Termiticide (active ingredient: bifenthrin) or Suspend Polyzone (active ingredient: deltamethrin) from May 17 to November 8, 2016. A total of 15,083 adult mosquitoes and 18,054 mosquito eggs were collected. Analysis of variance (P < 0.05) was used to analyze differences in abundance of key species between weeks, traps, and treatments. Weather trends were analyzed in relation to mosquito abundance using time-lagged weekly average temperatures and total rainfall. Kriging showed hot spots of mosquito abundance. The spatial pattern of abundance was different for oviposition and adults, and this was expected because of different types of traps used here. A land cover analysis was performed within the geographic information system (GIS) file to determine the extent to which land cover type could predict mosquito abundance. We show an uneven distribution of host-seeking mosquito abundance and that, in general, mosquitoes preferred areas that were lightly wooded or composed of small collections of trees or bushes, compared with larger densely wooded areas. Analyses of spatial distribution, land cover, and weather can be used to supplement an integrated mosquito management approach.

Bifurcation thresholds and optimal control in transmission dynamics of arboviral diseases

In this paper, we derive and analyse a model for the control of arboviral diseases which takes into account an imperfect vaccine combined with some other control measures already studied in the literature. We begin by analysing the basic model without control. We prove the existence of two disease-free equilibrium points and the possible existence of up to two endemic equilibrium points (where the disease persists in the population). We show the existence of a transcritical bifurcation and a possible saddle-node bifurcation and explicitly derive threshold conditions for both, including defining the basic reproduction number, [Formula: see text], which provides whether the disease can persist in the population or not. The epidemiological consequence of saddle-node bifurcation is that the classical requirement of having the reproduction number less than unity, while necessary, is no longer sufficient for disease elimination from the population. It is further shown that in the absence of disease-induced death, the model does not exhibit this phenomenon. The model is extended by reformulating the model as an optimal control problem, with the use of five time dependent controls, to assess the impact of vaccination combined with treatment, individual protection and two vector control strategies (killing adult vectors and reduction of eggs and larvae). By using optimal control theory, we establish conditions under which the spread of disease can be stopped, and we examine the impact of combined control tools on the transmission dynamic of disease. The Pontryagin's maximum principle is used to characterize the optimal control. Numerical simulations and efficiency analysis show that, vaccination combined with other control mechanisms, would reduce the spread of the disease appreciably.