Surveillance of malaria vector population density and biting behaviour in western Kenya

BACKGROUND: Malaria is a great public health burden and Africa suffers the largest share of malaria-attributed deaths. Despite control efforts targeting indoor malaria transmission, such as insecticide-treated bed nets (ITNs) and deployment of indoor residual spraying, transmission of the parasite in western Kenya is still maintained. This study was carried out to determine the impact of ITNs on indoor vector densities and biting behaviour in western Kenya. METHODS: Indoor collection of adult mosquitoes was done monthly in six study sites in western Kenya using pyrethrum spray collections from 2012 to 2014. The rotator trap collections were done in July–August in 2013 and May–June in 2014. Mosquitoes were collected every 2 h between 18.00 and 08.00 h. Human behaviour study was conducted via questionnaire surveys. Species within Anopheles gambiae complex was differentiated by PCR and sporozoite infectivity was determined by ELISA. Species distribution was determined and bed net coverage in the study sites was recorded. RESULTS: During the study a total of 5,469 mosquito vectors were collected from both PSC and Rotator traps comprising 3,181 (58.2%) Anopheles gambiae and 2,288 (41.8%) Anopheles funestus. Compared to all the study sites, Rae had the highest density of An. gambiae with a mean of 1.2 (P < 0.001) while Kombewa had the highest density of An. funestus with a mean of 1.08 (P < 0.001). Marani had the lowest density of vectors with 0.06 An. gambiae and 0.17 An. funestus (P < 0.001). Among the 700 PCR confirmed An. gambiaes.l. individuals, An. gambiaes.s. accounted for 49% and An. arabiensis 51%. Over 50% of the study population stayed outdoors between 18.00 and 20.00 and 06.00 and 08.00 which was the time when highest densities of blood fed vectors were collected. Anopheles gambies.s. was the main malaria parasite vector in the highland sites and An. arabiensis in the lowland sites. Bed net ownership in 2012 averaged 87% across the study sites. CONCLUSIONS: This study suggests that mass distribution of ITNs has had a significant impact on vector densities, species distribution and sporozoite rate. However, shift of biting time poses significant threats to the current malaria vector control strategies which heavily rely on indoor controls

The efficacy of long-lasting nets with declining physical integrity may be compromised in areas with high levels of pyrethroid resistance

Background: Long-lasting insecticide-treated mosquito nets (LLINs) are a primary malaria prevention strategy in sub-Saharan Africa. However, emergence of insecticide resistance threatens the effectiveness of LLINs. Methods. Cross-sectional surveys of LLINs were conducted in houses of seven and four villages in Gem and Bungoma Districts in western Kenya, respectively. Condition (number and area of holes in the nets), number and species of mosquitoes resting inside them, and insecticidal activity of nets were quantified. Mosquitoes collected inside nets were allowed to lay eggs and progeny tested for susceptibility to deltamethrin and permethrin, pyrethoids commonly deployed in LLINs in western Kenya. Results: In Gem, 83.3% of nets were less than three years old and 32.4% had at least one hole of any size; while in Bungoma, 92% were less than three years old and 48% had at least one hole. No anopheline and five Culex spp. mosquitoes were found resting inside nets in Gem regardless of the number and size of holes, while 552 Anopheles gambiae s.l., five Anopheles funestus s.l. and 137 Culex spp. were in nets in Bungoma. The number of mosquitoes resting inside nets increased with hole areas &gt;50 cm in Bungoma. In WHO resistance assays, f1 offspring of samples collected in nets in Bungoma were 94 and 65% resistant to deltamethrin and permethrin, respectively. Nets from Bungoma retained strong activity against a susceptible laboratory strain, but not against f1 offspring of field-collected An. gambiae s.s. All An. gambiae s.s. samples collected in nets were homozygous for the kdr genotype L1014S. Conclusions: In areas with pyrethroid resistant vectors, LLINs with modest hole areas permit mosquito entry and feeding, providing little protection against the vectors. LLIN formulations develop large holes within three years of use, diminishing their presupposed lifetime effectiveness. © 2013 Ochomo et al.; licensee BioMed Central Ltd

A high throughput multi-locus insecticide resistance marker panel for tracking resistance emergence and spread in Anopheles gambiae

The spread of resistance to insecticides in disease-carrying mosquitoes poses a threat to the effectiveness of control programmes, which rely largely on insecticide-based interventions. Monitoring mosquito populations is essential, but obtaining phenotypic measurements of resistance is laborious and error-prone. High-throughput genotyping offers the prospect of quick and repeatable estimates of resistance, while also allowing resistance markers to be tracked and studied. To demonstrate the potential of highly-mulitplexed genotypic screening for measuring resistance-association of mutations and tracking their spread, we developed a panel of 28 known or putative resistance markers in the major malaria vector Anopheles gambiae, which we used to screen mosquitoes from a wide swathe of Sub-Saharan Africa (Burkina Faso, Ghana, Democratic Republic of Congo (DRC) and Kenya). We found resistance association in four markers, including a novel mutation in the detoxification gene Gste2 (Gste2-119V). We also identified a duplication in Gste2 combining a resistance-associated mutation with its wild-type counterpart, potentially alleviating the costs of resistance. Finally, we describe the distribution of the multiple origins of kdr resistance, finding unprecedented diversity in the DRC. This panel represents the first step towards a quantitative genotypic model of insecticide resistance that can be used to predict resistance status in An. gambiae

Safety and mosquitocidal efficacy of high-dose ivermectin when co-administered with dihydroartemisinin-piperaquine in Kenyan adults with uncomplicated malaria (IVERMAL): a randomised, double-blind, placebo-controlled trial

BACKGROUND: Ivermectin is being considered for mass drug administration for malaria due to its ability to kill mosquitoes feeding on recently treated individuals. However, standard, single doses of 150-200 μg/kg used for onchocerciasis and lymphatic filariasis have a short-lived mosquitocidal effect (<7 days). Because ivermectin is well tolerated up to 2000 μg/kg, we aimed to establish the safety, tolerability, and mosquitocidal efficacy of 3 day courses of high-dose ivermectin, co-administered with a standard malaria treatment. METHODS: We did a randomised, double-blind, placebo-controlled, superiority trial at the Jaramogi Oginga Odinga Teaching and Referral Hospital (Kisumu, Kenya). Adults (aged 18-50 years) were eligible if they had confirmed symptomatic uncomplicated Plasmodium falciparum malaria and agreed to the follow-up schedule. Participants were randomly assigned (1:1:1) using sealed envelopes, stratified by sex and body-mass index (men: <21 vs ≥21 kg/m2; women: <23 vs ≥23 kg/m2), with permuted blocks of three, to receive 3 days of ivermectin 300 μg/kg per day, ivermectin 600 μg/kg per day, or placebo, all co-administered with 3 days of dihydroartemisinin-piperaquine. Blood of patients taken on post-treatment days 0, 2 + 4 h, 7, 10, 14, 21, and 28 was fed to laboratory-reared Anopheles gambiae sensu stricto mosquitoes, and mosquito survival was assessed daily for 28 days after feeding. The primary outcome was 14-day cumulative mortality of mosquitoes fed 7 days after ivermectin treatment (from participants who received at least one dose of study medication). The study is registered with ClinicalTrials.gov, number NCT02511353. FINDINGS: Between July 20, 2015, and May 7, 2016, 741 adults with malaria were assessed for eligibility, of whom 141 were randomly assigned to receive ivermectin 600 μg/kg per day (n=47), ivermectin 300 μg/kg per day (n=48), or placebo (n=46). 128 patients (91%) attended the primary outcome visit 7 days post treatment. Compared with placebo, ivermectin was associated with higher 14 day post-feeding mosquito mortality when fed on blood taken 7 days post treatment (ivermectin 600 μg/kg per day risk ratio [RR] 2·26, 95% CI 1·93-2·65, p<0·0001; hazard ratio [HR] 6·32, 4·61-8·67, p<0·0001; ivermectin 300 μg/kg per day RR 2·18, 1·86-2·57, p<0·0001; HR 4·21, 3·06-5·79, p<0·0001). Mosquito mortality remained significantly increased 28 days post treatment (ivermectin 600 μg/kg per day RR 1·23, 1·01-1·50, p=0·0374; and ivermectin 300 μg/kg per day 1·21, 1·01-1·44, p=0·0337). Five (11%) of 45 patients receiving ivermectin 600 μg/kg per day, two (4%) of 48 patients receiving ivermectin 300 μg/kg per day, and none of 46 patients receiving placebo had one or more treatment-related adverse events. INTERPRETATION: Ivermectin at both doses assessed was well tolerated and reduced mosquito survival for at least 28 days after treatment. Ivermectin 300 μg/kg per day for 3 days provided a good balance between efficacy and tolerability, and this drug shows promise as a potential new tool for malaria elimination. FUNDING: Malaria Eradication Scientific Alliance (MESA) and US Centers for Disease Control and Prevention (CDC)