Quantifying the impact of decay in bed-net efficacy on malaria transmission

Abstract

Insecticide-treated nets (ITNs) are at the forefront of malaria control programs and even though the percentage of households in sub-Saharan Africa that owned nets increased from 3% in 2000 to 53% in 2012, many children continue to die from malaria. The potential impact of ITNs on reducing malaria transmission is limited due to inconsistent or improper use, as well as physical decay in effectiveness. Most mathematical models for malaria transmission have assumed a fixed effectiveness rate for bed-nets, which can overestimate the impact of nets on malaria control. We develop a model for malaria spread that captures the decrease in ITN effectiveness due to physical and chemical decay, as well as human behavior as a function of time. We perform uncertainty and sensitivity analyses to identify and rank parameters that play a critical role in malaria transmission. These analyses show that the basic reproduction number R0, and the infectious human population are most sensitive to bed-net coverage and the biting rate of mosquitoes. Our results show the existence of a backward bifurcation for the case in which ITN efficacy is constant over time, which occurs for some range of parameters and is characterized by high malaria mortality in humans. This result implies that bringing R0 to less than one is not enough for malaria elimination but rather additional efforts will be necessary to control the disease. For the case in which ITN efficacy decays over time, we determine coverage levels required to control malaria for different ITN efficacies and demonstrate that ITNs with longer useful lifespans perform better in malaria control. We conclude that malaria control programs should focus on increasing bed-net coverage, which can be achieved by enhancing malaria education and increasing bed-net distribution in malaria endemic regions.

Optimal bed net use for a dengue disease model with mosquito seasonal pattern

“…Conversely, several other trials and mathematical studies show that bed net implementation alone is not the most advisable control measure() and could not even eliminate the disease, especially in highly endemic regions. () This is due to several factors, including improper handling and natural decline in efficacy over time, and also the interplay between ITNs and mosquito demography and feeding preferences . Furthermore, ITN success in malaria elimination could be (mathematically) hindered by the existence of a backward bifurcation,() which suggests that additional effort is required to eliminate the disease.…”

“…() This is due to several factors, including improper handling and natural decline in efficacy over time, and also the interplay between ITNs and mosquito demography and feeding preferences . Furthermore, ITN success in malaria elimination could be (mathematically) hindered by the existence of a backward bifurcation,() which suggests that additional effort is required to eliminate the disease. In Agusto et al, it has been shown that if at least 75% of the population adopts bed nets, malaria could be eliminated, while the analysis of model presented in Dembele and Yakubu revealed that malaria remains endemic when not more than 80% of the population is protected from mosquito bites.…”

Towards a mechanistic understanding of the synergistic effects of harvesting timber and non‐timber forest products

“…The threshold parameter is the equivalent of the vectorial and basic reproduction numbers in vector and epidemiological models (Van den Driessche & Watmough ; Ngonghala, Ngwa & Teboh‐Ewungkem ; Ngonghala, Teboh‐Ewungkem & Ngwa ; Ngonghala et al . ). Note that the equilibrium solutions of equation can also be obtained by setting the right‐hand side of the equation to zero and solving for x .…”

Optimal insecticide-treated bed-net coverage and malaria treatment in a malaria-HIV co-infection model

“…Female mosquitoes require blood meals to produce eggs and only anopheles mosquitoes transmit malaria. In order to transmit the disease, a female anopheles mosquito must have been infected in a previous blood meal from an infected person [15,18,24]. The disease remains a major burden in many parts of the world, with Africa and south-east Asia at high risk of malaria infection [36].…”

“…However, malaria is still of public health concern, with high mortality in children [36]. There is a wide range of malaria intervention strategies, some of which are: insecticide-treated nets [1,24], indoor residual spraying [34,36], anti-malarial drugs such as artemesinin combination therapy [32,36], and intermittent preventive treatment in children (IPTi) and in pregnant women (IPTp) [32]. Several studies have been conducted to investigate the efficacy and efficiency of these interventions as well as how best to integrate these control efforts in a fight against malaria (see [3,15,18,24,32,34] and references therein).…”