Nationwide assessment of insecticide susceptibility in Anopheles gambiae populations from Zimbabwe.

BACKGROUND: The scale-up of malaria interventions in sub-Saharan Africa has been accompanied by a dramatic increase in insecticide resistance in Anopheles spp. In Zimbabwe resistance to pyrethroid insecticides was reported in Gokwe District in 2008. This study reports results of the first nation-wide assessment of insecticide susceptibility in wild populations of Anopheles gambiae sensu lato (s.l.) in Zimbabwe, and provides a comprehensive review of the insecticide resistance status of An. gambiae s.l. in southern African countries. METHODS: World Health Organization (WHO) insecticide susceptibility tests were performed on 2,568 field collected mosquitoes originating from 13 sentinel sites covering all endemic regions in Zimbabwe in 2011-2012. At each site, 24-hour mortality and knock-down values for 50% and 90% of exposed mosquitoes (KD50 and KD90, respectively) were calculated for pools of 20-84 (mean, 54) mosquitoes exposed to 4% DDT, 0.1% bendiocarb, 0.05% λ-cyhalothrin or 5% malathion. Susceptibility results from Zimbabwe were compiled with results published during 2002-2012 for all southern African countries to investigate the resistance status of An. gambiae s.l. in the region. RESULTS: Using WHO criteria, insecticide resistance was not detected at any site sampled and for any of the insecticide formulations tested during the malaria transmission season in 2012. Knock-down within 1 hr post-insecticide exposure ranged from 95% to 100%; mortality 24 hours post-insecticide exposure ranged from 98% to 100%. Despite the lack of insecticide resistance, high variability was found across sites in KD50 and KD90 values. A total of 24 out of 64 (37.5%) sites in southern Africa with reported data had evidence of phenotypic insecticide resistance in An. gambiae s.l. to at least one insecticide. CONCLUSION: Despite a long history of indoor residual spraying of households with insecticide, up to 2012 there was no evidence of phenotypic resistance to any of the four insecticide classes in An. gambiae s.l. collected across different eco-epidemiological areas in Zimbabwe. Results reinforce the need for careful monitoring over time in sentinel sites in order to detect the potential emergence and propagation of insecticide resistance as insecticidal vector control interventions in Zimbabwe continue to be implemented

Biting behaviour of Anopheles funestus populations in Mutare and Mutasa districts, Manicaland province, Zimbabwe: Implications for the malaria control programme

Background & objectives: Biting behaviour of Anopheles funestus in Mutare and Mutasa districts, Zimbabwe, is little understood. An investigation was conducted to primarily compare indoor and outdoor biting behaviour of the mosquito, as well as blood meal sources and sporozoite rates. Methods: Monthly adult anopheline sampling was conducted from October 2013 to September 2014 using Centers for Disease Control light-traps, pyrethrum spray catch and artificial pit shelter methods. Mosquitoes sampled by light-traps were divided into two cohorts. In one cohort, traps were left overnight and mosquitoes were collected the following morning, while in the other set, mosquitoes were collected hourly from 1800-0600 hrs . Collected females were identified using morphological characters and categorised according to their abdominal status. Polymerase chain reaction was used to identify An. funestus sibling species and blood meal sources. Infection rate was tested by enzyme-linked immunosorbent assay. Results: Morphological identification showed that indoor and outdoor catches comprised Anopheles funestus (98.3%) and Anopheles gambiae s.l. (1.7%). Of the 2268 mosquitoes collected, 66.2% were caught by light-traps, and 33.8% were caught resting indoors and outdoors. Anopheles funestus and An. gambiae s.l. were trapped more abundantly indoors (68%) than outdoors (32%). Both indoor and outdoor An. funestus densities were higher in wet (4.3) than dry season (1.8). In Burma Valley and Zindi areas, An. funestus demonstrated variable nocturnal indoor and outdoor flight activity rhythms, with two peaks during the night; between 2200-2300 hrs and 0200- 0400 hrs. Human blood index in An. funestus was 0.64, with Plasmodium falciparum infection rate of 1.8%. Interpretation & conclusion: The present work highlighted important information on the host-seeking behaviour, blood meal sources and infection rates in An. funestus. The information would be helpful in improving the vector control strategies