Increasing insecticide resistance in Anopheles funestus and Anopheles arabiensis in Malawi, 2011–2015

Abstract

BackgroundSusceptibility of principal Anopheles malaria vectors to common insecticides was monitored over a 5-year period across Malawi to inform and guide the national malaria control programme.MethodsAdult blood-fed Anopheles spp. and larvae were collected from multiple sites in sixteen districts across the country between 2011 and 2015. First generation (F1) progeny aged 2–5 days old were tested for susceptibility, using standard WHO procedures, against pyrethroids (permethrin and deltamethrin), carbamates (bendiocarb and propoxur), organophosphates (malathion and pirimiphos-methyl) and an organochlorine (DDT).ResultsMortality of Anopheles funestus to deltamethrin, permethrin, bendiocarb and propoxur declined significantly over the 5-year (2011–2015) monitoring period. There was wide variation in susceptibility to DDT but it was not associated with time. In contrast, An. funestus exhibited 100% mortality to the organophosphates (malathion and pirimiphos-methyl) at all sites tested. There was reduced mortality of Anopheles arabiensis to deltamethrin over time though this was not statistically significant. However, mortality of An. arabiensis exposed to permethrin declined significantly over time. Anopheles arabiensis exposed to DDT were more likely to be killed if there was high ITN coverage in the mosquito collection area the previous year. There were no other associations between mosquito mortality in a bioassay and ITN coverage or IRS implementation. Mortality of An. funestus from four sites exposed to deltamethrin alone ranged from 2 to 31% and from 41 to 94% when pre-exposed to the synergist piperonyl butoxide followed by deltamethrin. For permethrin alone, mortality ranged from 2 to 13% while mortality ranged from 63 to 100% when pre-exposed to PBO.ConclusionPyrethroid resistance was detected in An. funestus and An. arabiensis populations across Malawi and has worsened over the last 5 years. New insecticides and control strategies are urgently needed to reduce the burden of malaria in Malawi.Electronic supplementary materialThe online version of this article (doi:10.1186/s12936-016-1610-1) contains supplementary material, which is available to authorized users.

The effectiveness of older insecticide-treated bed nets (ITNs) to prevent malaria infection in an area of moderate pyrethroid resistance: results from a cohort study in Malawi

“…Phenotypic and molecular evidence have demonstrated that pyrethroid resistance in An. funestus in Malawi is largely driven by oxidase enzymes that contribute to metabolic detoxification of pyrethroids [41,42]. In settings of moderate intensity of monooxygenase-based resistance, such as Malawi, the WHO recommends the deployment of ITNs with the synergist piperonyl-butoxide (PBO) [43].…”

Analysis of antibody responses to selected Plasmodium falciparum merozoite surface antigens in mild and cerebral malaria and associations with clinical outcomes

“…1 Mean and range of values: haemoglobin (Hb gl -1 ); haematocrit (%); Thr = thrombocytes (×10 3 ml -1 ); creat = creatinine (mg ml -1 ); bil = total bilirubin (mg ml -1 ); Glasgow score (Glas); % of parasitized erythrocytes (%pE); CM = cerebral malaria; MM = mild malaria; n.s. 4 Percentage of individuals with positive blood smear at recruitment. 2 Percentage of males.…”

“…3 Percentage of individuals who declared treatment before hospitalization. 4 Percentage of individuals with positive blood smear at recruitment. 5 Comparison of biological results (Mann-Whitney test).…”

“…Scaled-up control measures have contributed to a 48% decline in fatalities from an estimated 839 000 to 435 000 from 2000 to 2017, including a 63% decrease for children aged under 5 years [1]. However, this progress in many areas of Africa is threatened by parasite drug-resistance and anopheles vector insecticide resistance [2][3][4][5][6]. In addition, reduced exposure to the parasite results in waning natural immunity, increasing the risk of severe clinical outcomes in populations from endemic areas [7].…”

Behavioral response of insecticide-resistant mosquitoes against spatial repellent: a modified self-propelled particle model simulation

“…Pyrethroids, along with other pesticides, are also widely used to control agricultural pests on livestock and field crops worldwide [3]. The past decade has seen a dramatic increase in reports of physiological pyrethroid resistance in malaria vectors [4][5][6][7][8][9][10][11][12][13][14][15]. The rapid increase in pyrethroid resistance necessitates an immediate proactive resistance management response to avoid compromising existing effective interventions.…”