Efficacy of insecticides used in indoor residual spraying for malaria control: an experimental trial on various surfaces in a “test house”

Abstract

Background: Malaria is a public health problem in the Brazilian Amazon region. In integrated vector management for malaria (anopheline) control, indoor residual spraying (IRS) represents one of the main tools in the basic strategy applied in the Amazonian states. It is essential to understand the residual efficacy of insecticides on different surfaces to determine spray cycles, ensure their rational use, and prevent wastage. This study aimed to evaluate the residual efficacy of six insecticide formulations used in the National Malaria Control Programme on four different types of walls in a field simulation at a "test house". Methods: The tests were performed as a field-simulating evaluation at a "test house" built in the municipality of Macapá. Six insecticide formulations comprising four pyrethroids, a carbamate, and an organophosphate were used, and evaluated when applied on different wall surfaces: painted wood, unpainted wood, plastered cement, and unplastered cement. The insecticides were applied to the interior walls of the "test house" by a trained technician. Results: In the bioassays performed with pyrethroids, deltamethrin water-dispersible granules (WG) performed particularly well, presenting residual bioefficacy of 8 months on both wood surfaces after the IRS, whereas alphacypermethrin suspension concentrate (SC) and etofenprox wettable powder (WP) demonstrated residual bioefficacy of 4 months on at least one of the wood surfaces; however, the pyrethroid lambda-cyhalothrin WP showed a low residual bioefficacy (< 3 months) on all tested surfaces, demonstrating its inefficiency for areas with a long transmission cycle of malaria. For the carbamate-bendiocarb WP, residual bioefficacy for 3 months was achieved only on wood surfaces. In general, the organophosphate pirimifos-methyl capsule suspension (CS) demonstrated the best result, with a mortality rate < 80% over a period of 6 months on all surfaces tested. Conclusion: Insecticide efficiency varies among different types of surface; therefore, a "test house" is a valuable evaluation tool. This work highlights the usefulness of associating the residual efficacy of insecticides on the surfaces commonly found in houses in endemic areas, together with knowledge about the transmission cycle duration of the transmission cycle and the insecticide susceptibility of the vector. This association helps in the decision-making for the malaria control intervention regarding.

Insecticide-impregnated netting as a potential surface treatment: an alternative to insecticide spraying for control of the leishmaniasis vector Lutzomyia longipalpis (Diptera: Psychodidae)?

“…Although there is some evidence to suggest that acypermethrin degrades in UV [47] other studies have shown that repeated exposure to UV did not reduce the e cacy of the Interceptor netting [48]. In addition, the surface on which the insecticide is applied plays a signi cant role in determining the effectiveness of the insecticide treatment [42,49,50]. In addition, although the present study did not evaluate this aspect, as the netting was placed on a plywood substrate, its e cacy could have been affected by either the possible exposure to fungal growth encouraged by the proximity to damp wood or the interaction between the l-cypermethrin and the constituents of the plywood.…”

Vector-focused Approaches to Curb Malaria Transmission in the Brazilian Amazon: An Overview of Current and Future Challenges and Strategies

“…This product has a residual effect for 4 months requiring three annual applications [82]. In the Amazon, factors such as the operational cost of mobilizing teams to perform insecticide spraying, the difficulty in accessing remote areas at adequate frequency, the variability of dwellings, and variable environmental conditions, may compromise the efficacy of IRS [88]. In fact, few systematic evaluations on the impact these measures have on suppressing anopheline populations and reducing levels of malaria transmission in the Brazilian Amazon have been performed [82,88].…”

“…In the Amazon, factors such as the operational cost of mobilizing teams to perform insecticide spraying, the difficulty in accessing remote areas at adequate frequency, the variability of dwellings, and variable environmental conditions, may compromise the efficacy of IRS [88]. In fact, few systematic evaluations on the impact these measures have on suppressing anopheline populations and reducing levels of malaria transmission in the Brazilian Amazon have been performed [82,88]. While IRS is applicable and effective in urban and peri-urban environments, issues need to be addressed regarding gold miners who often live in huts without walls, continuously exposed to mosquito bites, unconventional indigenous house architecture that may not favor IRS and the lack of studies regarding the stability of insecticides applied on unconventional surfaces and under extreme humidity and temperature environmental conditions [89].…”

Previous Trend, Present Prevalence and Integrated Knowledge, Attitude and Practice Towards Malaria and Use of Insecticide-treated Mosquito Net in the Rural Setting of Welkait District, Northwest Ethiopia

“…Several reports indicated consistent and correct utilization of ITNs, particularly the LLINs proven to reduce the transmission rate up to 90% [11][12][13]. IRS is also an extremely effective means of malaria control strategy when properly applied in areas where malaria is epidemic [10,14]. In Ethiopia following the WHO recommendation, ITNs have been distributed in all malarious areas free of charge via health workers, volunteers and local administrators.…”