Abstract
Monitoring local mosquito populations for insecticide resistance is critical for effective vector-borne disease control. However, widely used phenotypic assays, which are designed to monitor the emergence and spread of insecticide resistance (technical resistance), do not translate well to the efficacy of vector control products to suppress mosquito numbers in the field (practical resistance). This is because standard testing conditions such as environmental conditions, exposure dose, and type of substrate differ dramatically from those experienced by mosquitoes under field conditions. In addition, field mosquitoes have considerably different physiological characteristics such as age and blood-feeding status. Beyond this, indirect impacts of insecticide resistance and/or exposure on mosquito longevity, pathogen development, host-seeking behavior, and blood-feeding success impact disease transmission. Given the limited number of active ingredients currently available and the observed discordance between resistance and disease transmission, we conclude that additional testing guidelines are needed to determine practical resistance—the efficacy of vector control tools under relevant local conditions— in order to obtain programmatic impact.
Highlights
Vector-borne diseases such as dengue, Zika, leishmaniasis, Lyme disease, and malaria account for more than 700,000 deaths annually (World Health Organization, 2020b)
Phenotypic resistance is the product of genotype by environment interactions, which play a crucial role in the expression of the resistance phenotype, referred to as practical resistance, with the effect not always being intuitive
Technical resistance is a heritable change in the organism that leads to reduced susceptibility in lab-controlled bioassays, whereas practical resistance is a heritable change in the organism that leads to mosquito control failure in programmatic settings following correct deployment of an insecticidal product
Summary
Vector-borne diseases such as dengue, Zika, leishmaniasis, Lyme disease, and malaria account for more than 700,000 deaths annually (World Health Organization, 2020b). The Zika outbreak in 2016 infected more than 130,000 people in Brazil alone (Pan American Health Organization / World Health Organization, 2017), and there are an estimated 96 million cases of dengue annually, with more than 3.9 billion people in over 128 countries at risk of contracting the disease (World Health Organization, 2020b). Despite intensified malaria control and elimination efforts over the past two decades, it has been 5 years without significant reduction in the number of malaria cases globally. Because of the current impact of COVID-19 pandemic on those efforts, the targets outlined in World Health Organization (WHO)’s Global Technical Strategy for Malaria 2016–2030
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