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The interaction between permethrin exposure and malaria infection affects the host-seeking behaviour of mosquitoes.

ABSTRACT: BACKGROUND:Insecticide-treated bed nets (ITNs) help to control malaria by mechanically impeding the biting of mosquitoes, by repelling and irritating them and by killing them. In contrast to spatial repellency, irritancy implies that mosquitoes contact the ITN and are exposed to at least a sub-lethal dose of insecticide, which impedes their further blood-seeking. This would weaken the transmission of malaria, if mosquitoes are infectious. METHODS:It was therefore tested whether sub-lethal exposure to permethrin impedes blood-feeding differently in uninfected mosquitoes and in mosquitoes carrying the non-transmissible stage (oocysts) or the infectious stage (sporozoites) of the malaria parasite Plasmodium berghei. In addition, as the degree of irritancy determines the dose of insecticide the mosquitoes may receive, the irritancy to permethrin of infected and uninfected mosquitoes was compared. RESULTS:In this laboratory setting, sub-lethal exposure to permethrin inhibited the blood-seeking behaviour of Anopheles gambiae mosquitoes for almost 48 h. Although infection by malaria did not affect the irritancy of the mosquitoes to permethrin at either the developmental stage or the infectious stage, both stages of infection shortened the duration of inhibition of blood-seeking. CONCLUSIONS:The results suggest that the impact of ITNs may be weaker for malaria-infected than for uninfected mosquitoes. This will help to understand the global impact of ITNs on the transmission of malaria and gives a more complete picture of the effectiveness of that vector control measure.

SUBMITTER: Thievent K

PROVIDER: S-EPMC6416862 | biostudies-literature | 2019 Mar

REPOSITORIES: biostudies-literature

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The interaction between permethrin exposure and malaria infection affects the host-seeking behaviour of mosquitoes.

Thiévent Kevin K Hauser Gaël G Elaian Obada O Koella Jacob C JC

Malaria journal 20190314 1

<h4>Background</h4>Insecticide-treated bed nets (ITNs) help to control malaria by mechanically impeding the biting of mosquitoes, by repelling and irritating them and by killing them. In contrast to spatial repellency, irritancy implies that mosquitoes contact the ITN and are exposed to at least a sub-lethal dose of insecticide, which impedes their further blood-seeking. This would weaken the transmission of malaria, if mosquitoes are infectious.<h4>Methods</h4>It was therefore tested whether su ...[more]

PMID: 30871559

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Project description:Characterizing persistent malaria transmission that occurs after the combined deployment of indoor residual spraying (IRS) and long-lasting insecticidal nets (LLINs) is critical to guide malaria control and elimination efforts. This requires a detailed understanding of both human and vector behaviors at the same temporal and spatial scale. Cross-sectional human behavior evaluations and mosquito collections were performed in parallel in Magude district, Mozambique. Net use and the exact time when participant moved into each of five environments (outdoor, indoor before bed, indoor in bed, indoor after getting up, and outdoor after getting up) were recorded for individuals from three different age groups and both sexes during a dry and a rainy season. Malaria mosquitoes were collected with CDC light traps in combination with collection bottle rotators. The percentage of residual exposure to host-seeking vectors that occurred in each environment was calculated for five local malaria vectors with different biting behaviors, and the actual (at observed levels of LLIN use) and potential (i.e. if all residents had used an LLIN) personal protection conferred by LLINs was estimated. Anopheles arabiensis was responsible for more than 74% of residents' residual exposure to host-seeking vectors during the Magude project. The other four vector species (An. funestus s.s., An. parensis, An. squamosus and An. merus) were responsible for less than 10% each. The personal protection conferred by LLINs prevented only 39.2% of the exposure to host-seeking vectors that survived the implementation of both IRS and LLINs, and it differed significantly across seasons, vector species and age groups. At the observed levels of bednet use, 12.5% of all residual exposure to host-seeking vectors occurred outdoor during the evening, 21.9% indoor before going to bed, almost two thirds (64%) while people were in bed, 1.4% indoors after getting up and 0.2% outdoor after leaving the house. Almost a third of the residual exposure to host-seeking vectors (32.4%) occurred during the low transmission season. The residual bites of An. funestus s.s. and An. parensis outdoors and indoor before bedtime, of An. arabiensis indoors when people are in bed, and of An. squamosus both indoors and outdoors, are likely to have sustained malaria transmission throughout the Magude project. By increasing LLIN use, an additional 24.1% of exposure to the remaining hosts-seeking vectors could have been prevented. Since An. arabiensis, the most abundant vector, feeds primarily while people are in bed, increasing net use and net feeding inhibition (through e.g. community awareness activities and the selection of more effective LLINs) could significantly reduce the exposure to remaining host-seeking mosquitoes. Nonetheless, supplementary interventions aiming to reduce human-vector contact outdoors and/or indoors before people go to bed (e.g. through larval source management, window and eave screening, eave tubes, and spatial repellents) will be needed to reduce residual exposure to the outdoor and early biting An. funestus s.s. and An. parensis.

Dataset Information

The interaction between permethrin exposure and malaria infection affects the host-seeking behaviour of mosquitoes.

Publications

The interaction between permethrin exposure and malaria infection affects the host-seeking behaviour of mosquitoes.

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