Browsing by Author "Lwetoijera, Dickson"

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Contrasting vector competence of three main East African Anopheles malaria vector mosquitoes for Plasmodium falciparum
(Scientific reports, 2025-01-17) Kweyamba, Prisca; Hofer, Lorenz; Kibondo, Ummi; Mwanga, Rehema; Sayi, Rajabu; Matwewe, Fatuma; Lwetoijera, Dickson; Tambwe, Mgeni; Moore, Sarah
There are three Anopheles mosquito species in East Africa that are responsible for the majority of malaria transmission, posing a significant public health concern. Understanding the vector competence of different mosquito species is crucial for targeted and cost-effective malaria control strategies. This study investigated the vector competence of laboratory reared strains of East African An. gambiae sensu stricto, An. funestus s.s., and An. arabiensis mosquitoes towards local isolates of Plasmodium falciparum infection. Mosquito feeding assays using gametocytaemic blood from local donors revealed significant differences in both prevalence and intensity of oocyst and sporozoite infections among the three vectors. An. funestus mosquitoes presented the highest sporozoite prevalence 23.5% (95% confidence interval (CI) 17.5–29.6) and intensity of infection 6-58138 sporozoites. Relative to An. funestus, the odds ratio for sporozoites prevalence were 0.46 (95% CI 0.25–0.85) in An. gambiae and 0.19 (95% CI 0.07–0.51) in An. arabiensis, while the incidence rate ratio for sporozoite intensity was 0.31 (95% CI 0.14–0.69) in An. gambiae and 0.66 (95% CI 0.16–2.60) in An. arabiensis. Our findings indicate that all three malaria vector species may contribute to malaria transmission in East Africa, with An. funestus demonstrating superior vector competence. In conclusion, there is a need for comprehensive malaria control strategies targeting major malaria vector species, an update of malaria transmission models to consider vector competence and evaluation of malaria transmission blocking interventions in assays that include An. funestus mosquitoes.
Susceptibility status of major malaria vectors to novaluron, an insect growth regulator South-Eastern Tanzania
(Pan African Medical Journal, 2022-04-05) Justinian, Amos; Muyaga, Letus; Ngowo, Halfan; Urio, Naomi; Vianney, John‑Mary; Lwetoijera, Dickson
Introduction: application of Insect Growth Regulator (IGR) such as pyriproxyfen has shown a promising result in controlling malaria transmitting mosquitoes through autodissemination technique. Novaluron that inhibits the chitin development at mosquito larval stage present a promising candidate IGR for rotation with pyriproxyfen to prevent a chance of resistance development. This study assessed the susceptibility of immature stages of Anopheles arabiensis, Anopheles gambiae and Anopheles funestus to novaluron. Methods: susceptibility bioassays using technical grade novaluron (98% active ingredient) were performed inside the semi-field system using first instar larvae of Anopheles species. For each tested species, a total of 1500 larvae were used in the bioassay. Concentration range of 0.01 mg/l to 2 mg/l of novaluron were tested to establish Lethal Concentration (LC) sufficient to kills 50%, 90% and 99% of the exposed larvae by using log-dose response analysis. Results: of the tested mosquitoes, Anopheles gambiae were highly susceptible to novaluron followed by An. arabiensis and then An. funestus. Lethal concentrations, LC50, LC90 and LC99 (95%CI) in mg/l for An. gambiae were 0.018, 0.332 and 2.001 respectively. For An. arabiensis were 0.026, 0.546 and 2.013; and for An. funestus were 0.032, 1.00 and 5.580. High larval mortality was recorded at high concentration (2mg/L), with 80% mortality within 3 days post exposure. Conclusion: the study demonstrates the efficacy of novaluron in controlling Anopheles mosquito species at immature stages via larval mortality. These findings warrant further testing of novaluron for autodissemination by different vector species for its inclusion in rotation to prevent development of resistance.
Using pastoralist community knowledge to locate and treat dry-season mosquito breeding habitats with pyriproxyfen to control Anopheles gambiae s.l. and Anopheles funestus s.l. in rural Tanzania
(Springer Nature, 2021-01-06) Lupenza, Eliza; Kihonda, Japhet; Limwagu, Alex; Ngowo, Halfan; Sumaye, Robert; Lwetoijera, Dickson
Fundamentally, larviciding with pyriproxyfen (PPF) has potential to complement Long Lasting Insecticide Nets (LLINs) and indoor residual sprays (IRS) in settings where resistance to pyrethroids and residual malaria transmission exist. In this study, we evaluated the field effectiveness of larviciding using PPF to reduce dry season productivity of mosquito breeding habitats that were located by pastoralists within the study area. Using pastoralist knowledge, dry season breeding habitats in Mofu village rural Tanzania were located and monitored for larval productivity for a period of 8 months before PPF intervention. During the intervention, six out of twelve breeding habitats were treated with Sumilarv 0.5G PPF granules. The impact of deposited PPF was monitored by recording emergence inhibition of larvae collected from treated habitats compared to the appropriate control group for a period of three months and half post-intervention. During baseline, the average proportion (+SD) of adult emerged was similar between two clusters, with (0.89 + 0.22) for the control cluster and (0.93 + 0.16) for the treatment cluster of breeding habitats. Following treatment with PPF, the average proportion (+SD) of adult emerged in the treated breeding habitats was significantly low (0.096 + 0.22) compared to adults that emerged from larvae in the untreated habitats (0.99 + 0.22) (p < 0.0001). Of all emerged adults, approximately 94% were An. gambiae s.l. and the remaining 6% were An. funestus s.l. This is the first study demonstrating the usefulness of engaging pastoralist community to locate and identify hard to find mosquito breeding habitats. Reduced productivity of the targeted habitats with PPF offers prospect of implementing PPF larviciding in dry season when habitats are few and permanent to control mosquito population in rural settings.