A New Classification System for the Actions of IRS Chemicals Traditionally Used For Malaria Control

Abstract

Knowledge of how mosquitoes respond to insecticides is of paramount importance in understanding how an insecticide functions to prevent disease transmission. A suite of laboratory assays was used to quantitatively characterize mosquito responses to toxic, contact irritant, and non-contact spatial repellent actions of standard insecticides. Highly replicated tests of these compounds over a range of concentrations proved that all were toxic, some were contact irritants, and even fewer were non-contact repellents. Of many chemicals tested, three were selected for testing in experimental huts to confirm that chemical actions documented in laboratory tests are also expressed in the field. The laboratory tests showed the primary action of DDT is repellent, alphacypermethrin is irritant, and dieldrin is only toxic. These tests were followed with hut studies in Thailand against marked-released populations. DDT exhibited a highly protective level of repellency that kept mosquitoes outside of huts. Alphacypermethrin did not keep mosquitoes out, but its strong irritant action caused them to prematurely exit the treated house. Dieldrin was highly toxic but showed no irritant or repellent action. Based on the combination of laboratory and confirmatory field data, we propose a new paradigm for classifying chemicals used for vector control according to how the chemicals actually function to prevent disease transmission inside houses. The new classification scheme will characterize chemicals on the basis of spatial repellent, contact irritant and toxic actions.

Impact of a Spatial Repellent on Malaria Incidence in Two Villages in Sumba, Indonesia

“…Such evidence of human health impact is a fundamental and essential component in the critical path of development of any vector control tool, [38][39][40][41] especially new paradigms such as SR. 4 If the crude estimate of protective efficacy shown here, about 52%, is verified in statistically robust cluster-randomized trials, this instrument of control would likely approximate that benefit associated with LLINs. 42 It is important to note this study was not intended to assess a practical method of delivery of a spatial repellent product in malaria control.…”

Larvicidal and irritant activities of hexane leaf extracts of Citrus sinensis against dengue vector Aedes aegypti L.

“…Despite progress in vaccine development, no effective and acceptable multi-valent vaccines are currently available against mosquito-borne diseases. The approach to combat these diseases largely relies on interruption of the disease transmission cycle by either destruction of the aquatic stages or by killing the adult mosquitoes using chemical insecticides [1,2] .…”

Abbreviations and acronyms

“…Behavioural avoidance does not have the same importance as physiological resistance but may be considered to be a contributing factor, leading to the avoidance of lethal doses of an insecticide (Chandre et al, 2000;Grieco et al, 2007). This type of response can be further divided into direct contact excitation (sometimes referred to as "irritancy"), and non-contact spatial repellency when insects move away from the insecticide-treated area before making direct contact (Chareonviriyaphap et al, 1997;Grieco et al, 2007).…”

“…To better approximate insect behaviour in natural field settings, numerous experiments have been made over many decades using specially constructed experimental huts (Smith, 1965;Rozendaal et al, 1989;Roberts and Alecrim, 1991;Bangs, 1999;Grieco et al, 2000Grieco et al, , 2007Polsomboon et al, 2008;Malaithong et al, 2010). Most experimental hut studies have been conducted to observe the behaviour of Anopheles mosquitoes; however, Grieco et al (2007) successfully demonstrated that chemical actions could be observed in experimental huts using Ae.…”

“…Most experimental hut studies have been conducted to observe the behaviour of Anopheles mosquitoes; however, Grieco et al (2007) successfully demonstrated that chemical actions could be observed in experimental huts using Ae. aegypti as a model system.…”