Browsing by Author "Chaki, Prosper"

Now showing 1 - 4 of 4

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.
Elevating larval source management as a key strategy for controlling malaria and other vector-borne diseases in Africa
(BMC, 2025-02-07) Okumu, Fredros; Moore, Sarah; Selvaraj, Prashanth; Yafin, Arnon; Juma, Elijah; Shirima, GloriaSalome; Majambere, Silas; Hardy, Andy; Knols, Bart; Msugupakulya, Betwel; Finda, Marceline; Kahamba, Najat; Thomsen, Edward; Ahmed, Ayman; Zohdy, Sarah; Chaki, Prosper; DeChant, Peter; Fornace, Kimberly; Govella, Nicodem; Gowelo, Steven; Hakizimana, Emmanuel; Hamainza, Busiku; Ijumba, Jasper; Jany, William; Kafy, Hmooda; Kaindoa, Emmanuel; Kariuki, Lenson; Kiware, Samson; Kweka, Eliningaya; Lobo, Neil; Marrenjo, Dulcisária; Matoke-Muhia, Damaris; Mbogo, Charles; McCann, Robert; Monroe,n April; Ndenga, Bryson; Ngowo, Halfan; Ochomo, Eric; Opiyo, Mercy; Reithinger, Richard; Sikaala, Chadwick; Tatarsky, Allison; Takudzwa, David; Trujillano, Fedra; Sherrard-Smith, Ellie
Larval source management (LSM) has a long history of advocacy and successes but is rarely adopted where funds are limited. The World Health Organization (WHO) guidelines on malaria prevention recommend the use of LSM as a supplementary intervention to the core vector control methods (insecticide-treated nets and indoor residual spraying), arguing that its feasibility in many settings can be limited by larval habitats being numerous, transient, and difficult to find or treat. Another key argument is that there is insufficient high-quality evidence for its effectiveness to support wide-scale implementation. However, the stagnation of progress towards malaria elimination demands that we consider additional options to the current emphasis on insecticidal commodities targeting adult mosquitoes inside homes. This letter is the result of a global, crossdisciplinary collaboration comprising: (a) detailed online expert discussions, (b) a narrative review of countries that have eliminated local malaria transmission, and (c) a mathematical modeling exercise using two different approaches. Together, these efforts culminated in seven key recommendations for elevating larval source management as a strategy for controlling malaria and other mosquito-borne diseases in Africa (Box 1). LSM encompasses the use of larvicide (a commodity) as well as various environmental sanitation measures. Together, these efforts lead to the long-term reduction of mosquito populations, which benefits the entire community by controlling both disease vector and nuisance mosquitoes. In this paper, we argue that the heavy reliance on large-scale cluster-randomized controlled trials (CRTs) to generate evidence on epidemiological endpoints restricts the recommendation of approaches to only those interventions that can be measured by functional units and deliver relatively uniform impact and, therefore, are more likely to receive financial support for conducting these trials. The explicit impacts of LSM may be better captured by using alternative evaluation approaches, especially high-quality operational data and a recognition of locally distinct outcomes and tailored strategies. LSM contributions are also evidenced by the widespread use of LSM strategies in nearly all countries that have successfully achieved malaria elimination. Two modelling approaches demonstrate that a multifaceted strategy, which incorporates LSM as a central intervention alongside other vector control methods, can effectively mitigate key biological threats such as insecticide resistance and outdoor biting, leading to substantial reductions in malaria cases in representative African settings. This argument is extended to show that the available evidence is sufficient to establish the link between LSM approaches and reduced disease transmission of mosquito-borne illnesses. What is needed now is a significant boost in the financial resources and public health administration structures necessary to train, employ and deploy local-level workforces tasked with suppressing mosquito populations in scientifically driven and ecologically sensitive ways. In conclusion, having WHO guidelines that recognize LSM as a key intervention to be delivered in multiple contextualized forms would open the door to increased flexibility for funding and aid countries in implementing the strategies that they deem appropriate. Financially supporting the scale-up of LSM with high-quality operations monitoring for vector control in combination with other core tools can facilitate better health. The global health community should reconsider how evidence and funding are used to support LSM initiatives.
Laboratory efficacy of Bactivec ® and Griselesf ® biolarvicides used for large-scale larviciding in Tanzania
(Frontiers, 2025-07-21) Tegemeo, Gavana; Kailembo, Denis; Machange, Jane; Venance Michael; Swai, Kyeba; Olukayode, Odufuwa; Tenywa, Frank; Mwalimu, Charles; Jubilate Bernard; Samwel Lazaro; Best Yoram; Kajange, Stella; Kasagama, Elizabeth; Kisoka, Noela; Mbuba, Emmanuel; Chaki, Prosper; Lengeler, Christian; Moore, Sarah
From 2022 to 2024, a project piloting large-scale larviciding in Tanzania was implemented in Tanga Region. The project used in-country manufactured biolarvicides, The study was conducted at Ifakara Health Institute (IHI) in Tanzania. Laboratory-based dose–response experiments were performed using Bactivec® and Griselesf® against laboratory-reared early third instar larvae of Anopheles gambiae sensu stricto, Anopheles arabiensis, Anopheles funestus, Aedes aegypti and Culex quinquefasciatus. Larvae were exposed to various concentrations of Bactivec® and Griselesf®. VectoBac® served as a positive control, and distilled water as a negative control. Twelve replicates per concentration, with 25 larvae per replicate, were tested. Larval mortality was recorded at 24 and 48 hours after exposure to Bactivec® and Griselesf®, respectively. Probit regression analysis was used to determine the lethal concentration (LC50 and LC90) values.Bactivec® and Griselesf®. This study independently assessed the efficacy of both biolarvicide products to ensure that they represented a good option for scaling up.
Modelling the impact of larviciding as a supplementary malaria vector control intervention in rural south-eastern Tanzania: A district-level simulation study
(medRxiv, 2025-11-15) Shirima, GloriaSalome; Fairbanks, Emma; Tegemeo, Gavana; Kiwelu, Gerald; Nambunga, Ismail; Mlacha, Yeromin; Mirau, Silas; Chaki, Prosper; Chitnis, Nakul; Kiware, Samson
Combining larviciding with insecticide treated nets (ITNs) can reduce malaria transmission, but 42 most modelling analyses use generalized scenarios rather than local contexts. In Tanzania and 43 other countries, larviciding is increasingly being prioritized in national strategies, with growing 44 advocacy for its broader implementation, to achieving sustained malaria reduction. District- 45 specific modelling is therefore essential to capture variation in transmission ecology, seasonality, 46 and varying coverage levels, providing evidence that is both rigorous and actionable for malaria 47 control programs. The Vector Control Optimization Model (VCOM) was adapted and extended to 48 incorporate local seasonality, simulating the impact of larviciding across a range of coverage levels 49 combined with ITNs. The model was parameterized using district-level field-data on mosquito 50 mortality collected before (2016-2017) and after (2019-2021) larviciding implementation. 51 Mosquito mortality rates were estimated using Bayesian inference. Outcomes were evaluated 52 specifically for Anopheles gambiae s.l. including annual entomological inoculation rates (EIR) and 53 mosquito density. Sensitivity analysis explored the influence of key parameters driving 54 transmission in this scenario study. The immature mosquito mortality rate due to larviciding is 55 estimated to be 61% based on field data. VCOM simulation showed that, at 80%, ITNs coverage, 56 larviciding substantially reduced mosquito densities and EIR. Specifically, combining ITNs at 57 80% and larviciding coverage ≥ 60% lowered EIR below 1, the threshold required to interrupt 58 malaria transmission. Sensitivity analyses highlighted the high impact of targeting immature 59 mosquitoes, suggesting larviciding can effectively complement ITNs to control vectors, including 60 invasive species like An. stephensi, regardless of feeding preference, resting, and biting behaviors, 61 which hinder the effectiveness of most vector control tools. This study provides local evidence 62 that larviciding is an effective complement to ITNs for interrupting malaria transmission. 63 Implementation should leverage innovative approaches, such as drones for precise mapping and 64 targeted application of biological larvicides, to maximize coverage, and scalability for district- 65 level malaria control and elimination