Browsing by Author "Mlacha, Yeromin"

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Modelling the impact of different intervention packages for malaria control under varying intensities of pyrethroid resistance
(Malaria Journal, 2025-11-19) Gervas, Hamenyimana; Mayengo, Maranya; Mlacha, Yeromin; Ngowo, Halfan; Okumu, Fredros; Selvaraj, Prashanth
Background Malaria control in sub-Saharan Africa faces significant challenges from biological threats, such as insec- ticide resistance and adaptive vector behaviours, as well as increasing financial constraints, which necessitate stra- tegic intervention planning to maximize impact. This study assesses the effectiveness of combining vector control methods, case management, and immunoprevention to reduce malaria in Tanzania, considering varying intensities of insecticide resistance in the main vector species. Methods A compartmental model was developed to simulate malaria transmission, incorporating the dominant vectors: Anopheles funestus (anthropophilic and endophilic) and Anopheles arabiensis (zoophilic and exophilic). The model was used to analyse the impacts of insecticide-treated nets (ITNs), indoor residual spraying (IRS), and biolar- vicides, used singly or in combinations, under varying intensities of pyrethroid resistance. The analysis was further expanded to explore the impacts of adding case management (treatment using artemisinin-based combinations) and immunization (RTS,S/AS01 and R21/Matrix-M vaccines). Results At moderate levels of pyrethroid resistance (50%), achieving at least 71% ITN coverage combined with either 50% IRS or 32% biolarvicide coverage reduces the effective reproduction number (Re ) to below 1. How- ever, at high resistance levels (exceeding 75%), the effective reproduction number (Re ) consistently remains above 1, irrespective of the type or combination of vector control interventions. Adding immunization (≥ 40% coverage) to ITNs (80% coverage), along with effective treatment (80% coverage), can further reduce the proportion of infec- tious individuals to <20% and Re below 1, even under high resistance intensities. Conclusions Compared to ITNs alone, combining ITNs with IRS and/or biolarvicides greatly improves malaria control at low to moderate intensities of pyrethroid resistance but yields no additional benefits at high resistance intensi- ties. However, integrating these vector control strategies with immunization and effective case management using artemisinin-based combination therapy (ACT) further enhances impact by reducing both parasite transmission and the infectious reservoir
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
Risk of Aedes-borne diseases in and around the Tanzanian seaport of Tanga despite community members being more concerned about malaria
(BioMed Central, 2024-12-18) Abas, Amri; Simfukwe, Alfred; Masalu, John; Kahamba, Najat; Nambunga, Ismail; Msaky, Dickson; Limwagu, Alex; Kipekepeke, Abdallah; Wergin, Carsten; Njalambaha, Rukiyah; Kemibala, Elison; Seleman, Amour; Mlacha, Yeromin; Finda, Marceline; Beisel, Uli; Kimaro, Esther; Ngowo, Halfan; Okumu, Fredros
Background Increased global trade, while beneficial economically, can also increase the spread of vector-borne diseases, particularly those transmitted by Aedes mosquitoes spreading via trade routes. Given the heightened trade- induced activity at ports of entry, it is particularly crucial to assess the risk of mosquito-borne diseases in these set- tings. This study compared the risks of Aedes-borne disease in and around the eastern Tanzanian seaport of Tanga. Methods A 200 m × 200 m grid-based system was used to sample mosquitoes within the port area, and in surround- ing areas at 2 km, 2.5 km, and 5 km away, between June and December 2023. We characterized mosquito breeding habitats, collected mosquito larvae using standard dippers and tested susceptibility of raised adult Aedes aegypti populations to different insecticides. Adult mosquitoes were collected using BG sentinel traps (daytime) and Centers for Disease Control (CDC) light traps (night-time). Additionally, more than 200 port users and neighboring residents were surveyed to assess their experiences with and perceptions of mosquito biting and disease risks. Results There were 2931 breeding sites, with (60.8%, n = 1782) positive for Aedes larvae. The percentage of water- holding containers infested with Aedes immatures, i.e., the container index (CI), was highest in the port area (66.2%), and lowest 5 km away (44.6%). The port area also had a greater proportion of temporary breeding sites (64.9%) than did the surrounding areas. The adult mosquito surveys revealed 20,449 mosquito species including: Culex quinquefasciatus (56.2%), Mansonia uniformis (38.6%), Ae. aegypti (5.1%), Anopheles gambiae (0.1%), and Anoph- eles funestus. Ae. aegypti were more abundant in the port area than in the surrounding areas (P < 0.001), whereas Culex sp., and Mansonia sp., were significantly outside (P < 0.001). Adult Anopheles sp., were found only in the port area, but Anopheles larvae were found both within and outside the port areas. Tests on Ae. aegypti sp., revealed susceptibility to bendiocarb and DDT, and resistance to permethrin. Awareness of mosquito-borne diseases among respondents was high for malaria (64.8%), but low for dengue (26.3%) and Chikungunya (1.7%). Most respond- ents reported being bothered by mosquitoes mostly at night (53.4%) or in the evening (40.7%). In addition to insecti- cidal bednets, which are used primarily against malaria, preventive measures for Aedes-borne diseases are limited. Conclusions This study identified significant potential risk of Aedes species, specifically Ae. aegypti sp., and associated diseases, but low perception of risk and inadequate personal protection measures in the study area. This low percep- tion of risk highlights the need to improve public knowledge of the transmission and control of Aedes-borne diseases.