Browsing by Author "Muyaga, Letus"

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Characterization of a new laboratory colony of Anopheles funestus mosquitoes established in Ifakara, Tanzania
(bioRxiv, 2025-11-24) Hape, Emmanuel; Njalambaha, Rukiyah; Muyaga, Letus; Nambunga, Ismail; Mgando, Joseph; Mwasheshi, Dickson; Nombo, Neema; Mabula, Daniel; Zengenene, Munyaradzi; Kahamba, Najat; Odero, Joel; Ngowo, Halfan; Mapua, Salum; Chaki, Prosper; Govella, Nicodem; Lyimo, Issa; Kiware, Samson; Lwetoijera, Dickson; Tarimo, Brian; Kaindoa, Emmanuel; Selvaraj, Prashanth; Tripet, Frederic; Wondji, Charles; Baldini, Francesco; Koekemoer, Lizette; Ferguson, Heather; Okumu, Fredros O.
Background: Anopheles funestus, a major vector of malaria in Africa, has proven difficult to colonize in laboratory settings, impeding research on its biology and control. After several attempts, our team recently succeeded in colonizing a strain of An. funestus from Tanzania (FUTAZ). The objective of this study was to analyse the key fitness and genotypic characteristics of these mosquitoes during multiple filial generations of laboratory adaptation and compare them to wild An. funestus from Tanzania and a pre-existing colony of An. funestus from Mozambique (FUMOZ). Methods: Measures of mating success (percentage of female mosquitoes inseminated), body size (wing length), fecundity (number of eggs laid per female), and insecticide susceptibility (percentage of 24-hour mortality after exposure to insecticides) were compared between the newly established colonies of Tanzanian An. funestus (FUTAZ colonies), the long-established FUMOZ colonies, and a colony of Anopheles arabiensis maintained in the same laboratory. The maternal lineages of the An. funestus mosquitoes were investigated through a hydrolysis probe analysis of their mitochondrial DNA to identify distinct clades, I and II. Additionally, other intragenomic variations were examined through a PCR analysis of restriction fragment length polymorphisms (RFLP) on the third domain of 28S ribosomal DNA. These molecular markers were used to compare the FUTAZ colonies, FUMOZ colonies in Tanzania and South Africa, and the wild-collected An. funestus from Tanzania. Result: The mating success and body size of FUTAZ females declined significantly from filial generations F1 to F6 relative to the founder population (F0), but then increased from F7 onwards eventually matching FUMOZ by F9. Fecundity was similar across all colonies tested. However, it took significantly longer for 50% of the females in the FUTAZ and FUMOZ colonies (over 10 days) to mate compared to females in the An. arabiensis colony (approximately 5 days). Insecticide resistance appeared to be lost during colonization, but this varied with insecticide classes. Majority of mosquitoes in the FUTAZ colony, as well as the wild-caught Tanzanian An. funestus belonged to Clade I (80.4-89.4%) and RFLP type “Y” (90.5-91.4%), while the FUMOZ colonies were mostly Clade II (65.5-88.5%) and RFLP type “MW” (90.5-91.5%). Conclusion: This study suggests that the mating success and body size of An. funestus decreases significantly during the early stages of colonization, then increase as the mosquitoes adapt to laboratory conditions. It is therefore crucial to have a large enough founder population to persist through these early generations in order to achieve stable colonization of An. funestus. The Clade and RFLP genotyping demonstrated the genetic similarities between the FUTAZ mosquitoes and wild- caught Tanzanian An. funestus, but also showed that the new colony can be distinguished from the FUMOZ colony.
Common predators and factors influencing their abundance in Anopheles funestus aquatic habitats in rural south-eastern Tanzania
(PLOS ONE, 2023-06-26) Mahenge, Herieth; Muyaga, Letus; Nkya, Joel; Kifungo, Khamis; Kahamba, Najat; Ngowo, Halfan; Kaindoa, Emmanuel
Background The role of larval predators in regulating the Anopheles funestus population in various malaria-endemic countries remains relatively unknown. This study aimed to investigate the common predators that co-exist with Anopheles funestus group larvae and evaluate factors that influence their abundance in rural south-eastern Tanzania. Methods Mosquito larvae and predators were sampled concurrently using standard dipper (350 ml) or 10 L bucket in previously identified aquatic habitats in selected villages in southern Tan zania. Predators and mosquito larvae were identified using standard identification keys. All positive habitats were geo-located and their physical features characterized. Water physico chemical parameters such as dissolved oxygen (DO), pH, electrical conductivity (EC), total dissolved solids (TDS) and temperature were also recorded. Results A total of 85 previously identified An. funestus aquatic habitats in nine villages were sampled for larvae and potential predators. A total of 8,295 predators were sampled. Of these Coena grionidae 57.7% (n = 4785), Corixidae 12.8% (n = 1,060), Notonectidae 9.9% (n = 822), Aeshnidae 4.9% (n = 405), Amphibian 4.5% (n = 370), Dytiscidae 3.8% (n = 313) were com mon. A total of 5,260 mosquito larvae were sampled, whereby Anopheles funestus group were 60.3% (n = 3,170), Culex spp. 24.3% (n = 1,279), An. gambie s.l. 8.3% (n = 438) and other anophelines 7.1% (n = 373). Permanent and aquatic habitats larger than 100m2 were positively associated with An. funestus group larvae (P<0.05) and predator abundance(P<0.05). Habitats with submerged vegetation were negatively associated with An. funestus group larvae (P<0.05). Only dissolved oxygen (DO) was positively and significantly affect the abundance of An. funestus group larvae (P<0.05). While predators’ abundance was not impacted by all physicochemical parameters. Conclusion Six potential predator families were common in aquatic habitats of An. funestus group lar vae. Additional studies are needed to demonstrate the efficacy of different predators on lar val density and adult fitness traits. Interventions leveraging the interaction between mosquitoes and predators can be established to disrupt the transmission potential and sur vival of the An. funestus mosquitoes
Heterogeneous malaria transmission patterns in southeastern Tanzania driven by socio-economic and environmental factors
(BMC, 2025-05-29) Mukabana, Linda; Mshani, Issa; Gachohi, John; Minja, Elihaika; Jackson, Frank; Kahamba, Najat; Pinda, Polius; Muyaga, Letus; Msaky, Dickson; Ngowo, Halfan; Mambo, Susan; Olwendo, Amos; Bisanzio, Donal; Okumu, Fredros
Background As malaria-endemic countries progress towards elimination, distinct patterns of heterogeneous transmission are emerging. In south-eastern Tanzania, despite intensive control efforts, localized transmission shows prevalence ranging from under 1% to over 50% among nearby villages. This study investigated the socioeconomic and environmental factors driving this spatial heterogeneity. Methods A cross-sectional survey was conducted in the Kilombero and Ulanga districts of south-eastern Tanzania between 2022 and 2023, screening 3,249 individuals (ages 5–60) across 10 villages for malaria using rapid diagnostic tests (RDTs). Socioeconomic data was collected from all surveyed households and villages via questionnaires, while environmental data were obtained from remote sensing data sources. Associations between socioeconomic factors and malaria infection were analysed using a zero-inflated negative binomial model and employed a generalized additive model (GAM) to assess the impact of rainfall, and temperature on malaria infection. Results Greater elevation and higher rainfall were positively associated with malaria infection (OR = 1.68, 95% CI 1.38–2.05, p < 0.001 and OR = 1.46, 95% CI 1.14–1.87, p < 0.05 respectively), while temperature showed no significant effect (OR = 0.70, 95% CI 0.51–1.13, p = 0.117). Households in densely vegetated areas had higher malaria infections compared to those in more developed, built-up areas. At the individual level, males had a higher prevalence (355; 28.6%) and displayed significantly greater odds of infection (OR = 1.53, 95% CI 1.15–2.03, p < 0.05) than females (433; 21.6%). School-aged children (5–17 years) had a higher prevalence (36.9%) compared to adults (18–60 years) (15.9%). The probability of infection declined with increasing age (OR = 0.28, 95% CI 0.25–0.31, p < 0.001). Larger household sizes (more than four members) were positively associated with malaria infection (OR = 1.72, 95% CI 1.29–2.29, p < 0.001). Open-eave housing was associated with higher odds of malaria, whereas closed eaves (OR = 0.56, 95% CI 0.38–0.82, p < 0.05) and metal roofs (OR = 0.62, 95% CI 0.44–0.87, p < 0.05) were protective factors. Open water sources were positively associated with malaria infection compared to protected water sources (OR = 0.57, 95% CI 0.38–0.85, p < 0.05). Lack of bed net use was positively associated with malaria but this was not statistically significant (OR = 1.54, 95% CI 0.68–3.48, p = 0.299). Conclusion This study highlights the complex interplay between socioeconomic and environmental factors contributing to the fine-scale spatial heterogeneity of malaria in south-eastern Tanzania. Understanding these localized drivers is essential for designing targeted, effective strategies that support broader malaria elimination goals.
Semi-field evaluation of aquatic predators for the control of Anopheles funestus in rural south-eastern Tanzania
(Springer Nature, 2024-08-02) Mahenge, Herieth; Muyaga, Letus; Nkya, Joel; Kafwenji, Andrew; Mwalugelo, Yohana; Kahamba, Najat; Ngowo, Halfan; Kaindoa, Emmanuel
Background Biological control is a promising alternative or complementary approach for controlling vector populations in response to the spread of insecticide resistance in malaria vectors. This study evaluated the efficacy of three selected potential predators on the density and fitness parameters of Anopheles funestus larvae in rural Tanzania. Methods Common predator families Aeshnidae (dragonflies), Coenagrionidae (damselflies), and Notonectidae (backswimmers) and An. funestus group larvae were collected from natural aquatic habitats in rural south-eastern Tanzania. Predators were starved for 12-h while An. funestus larvae were given fish food before starting the experiment. Anopheles funestus larvae were placed into artificial habitats containing predators, exposing them to potential predation. The number of surviving An. funestus larvae were counted every 24-h. An emergence traps were placed at the top of artificial habitats to capture emerging mosquitoes. Emerged mosquitoes were monitored until they died. Female wings were measured and used as a proxy for body size. Generalized linear mixed models (GLMM) with binomial variates at 95% CI and Cox proportional hazard models were used to assess the proportion of dead mosquitoes and the daily survival determined. Results There were significant differences in the number of emerged mosquitoes between the treatment and control groups (P<0.001). Thus, all predator species played a significant role in reducing the density of An. funestus mosquitoes (P<0.001). Furthermore, these predators had notable effects on the fitness parameters and survival of emerged mosquitoes (P<0.001). Among the three predators studied, Coenagrionidae (damselflies) were most efficient followed by Notonectidae (backswimmers), with Aeshnidae (dragonflies) being the least efficient. Conclusion Selected aquatic predators have the potential to reduce the survival and density of An. funestus larvae. They might eventually be included within an integrated malaria vector control strategy, ultimately leading to a reduction in malaria transmission.
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.