A costing analysis of an intermittent biolarviciding intervention with limited epidemiological effect in Tanga Region, Tanzania

Diarra et al. Malaria Journal (2025) 24:352 https://doi.org/10.1186/s12936-025-05553-w Malaria Journal Open Access RESEARCH A costing analysis of an intermittent biolarviciding intervention with limited epidemiological effect in Tanga Region, Tanzania Sophie Diarra1,2†, Denis Kailembo1,2*†, Yahya Derua3, Tegemeo Gavana1,2,4, Best Yoram5, Stella Kajange5, Jubilate Bernard6, Charles Dismas6, Samwel Lazaro6, Elizabeth Kasagama1,2, Noela Kisoka1,2, Prosper Chaki4 and Christian Lengeler1,2 Abstract Background Malaria vector control strategies in sub-Saharan Africa have largely relied on the use of Insecticide Treated-mosquito Nets and Indoor Residual Spraying. However, after substantial reductions in malaria burden associated with the scale-up of these interventions, little progress has been achieved over the last decade. With the increase in insecticide resistance and outdoor biting of mosquitoes, larviciding offers the possibility to be an additional malaria control tool. This study is part of a comprehensive evaluation and aimed to assess prospectively the financial cost of a large-scale biolarviciding intervention in North-Eastern Tanzania. Methods Biolarviciding was carried out from June 2022 to April 2024 in three councils in Tanga Region, Tanzania: Handeni District Council (DC), Tanga City Council (CC) and Lushoto DC. The intervention area covered 10,396 km2, with a population of 1,059,384 living in 70 wards. Implementation followed a community-based approach, whereby Community-Owned Resource Persons (CORPs) identified breeding habitats and applied biolarvicides for three rounds per year, based on the prevailing rainfall patterns, whereby each round comprised of 8 consecutive weeks of application. Costing data were obtained from budgets, receipts of actual expenditure and discussions with finance administrators of the project. A micro-costing approach was used to calculate the total cost of the intervention, cost per person protected per year (cost pppy), and cost of projected scale-up. Results The total cost of this intermittent biolarviciding intervention in the three councils over the two years was 3,354,672,133 TZS (1,397,198 USD), with an average cost pppy of 1,583 TZS (0.66 USD). One-way sensitivity analysis showed that the cost of the procurement of biolarvicide had the greatest impact on the total cost. Continuous application of biolarviciding for six rounds per year would result in a cost pppy of 2,716 TZS (1.13 USD). Scale-up to all councils in the country would cost between 97,689,865,621 TZS (40,687,158 USD) and 167,582,345,528 TZS (69,796,895 USD) for three and six annual spray rounds, respectively. † Sophie Diarra and Denis Kailembo are joint first authors. *Correspondence: Denis Kailembo Full list of author information is available at the end of the article © The Author(s) 2025, corrected publication 2025. Open Access This article is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License, which permits any non-commercial use, sharing, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if you modified the licensed material. You do not have permission under this licence to share adapted material derived from this article or parts of it. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by-nc-nd/4.0/. Diarra et al. Malaria Journal (2025) 24:352 Page 2 of 11 Conclusions With the intermittent mode of implementation, yearly per capita costs of biolarviciding with Bacillus thuringiensis var israelensis and Bacillus sphaericus are likely to be financially feasible for scaling of the intervention in Tanzania. However, in separate publications the entomological and epidemiological impact of the intervention were found to vary according to settings, and hence the case for upscaling will crucially depend on determining impact in a given setting. Under this condition, biolarviciding could provide an additional complementary vector control tool for further reductions in malaria transmission and addressing the rise in outdoor malaria transmission. Keywords Malaria, Bacillus thuringiensis var israelensis, Bacillus sphaericus, Vector control, Cost analysis, Larviciding, Tanzania Background Malaria remains a large contributor to morbidity and child mortality in sub-Saharan Africa, despite global efforts to prevent and treat it. Total malaria cases and incidence have increased since 2020, with 94% of cases occurring in sub-Saharan Africa [1]. Tanzania is classified as a high burden malaria country, accounting for about 8.5 million (3.3%) of global cases in 2023 [1]. Globally, malaria vector control efforts have included mainly Insecticide-Treated mosquito Nets (ITNs) and Indoor Residual Spraying (IRS), in line with World Health Organization (WHO) guidance. Whilst effective [2, 3], malaria burden has remained relatively stable since 2015 suggesting new strategies are required [1]. The WHO has noted stagnation in malaria cases and deaths both globally and in the African region within this time-frame [1]. Moreover, over the past five years, many countries in the African region including Cameroon, Democratic Republic of the Congo, Ethiopia, Madagascar, Mali, Nigeria, Tanzania, and Uganda have reported increases in malaria cases [1]. Additionally, there are challenges with ongoing core malaria vector control interventions, including insecticide resistance and outdoor mosquito biting [4–6]. Larval source management including larviciding, has high potential to be included as a key strategy in the vector control toolbox, particularly for addressing malaria transmission linked to outdoor biting mosquitoes [7]. Specifically, biolarvicides based on mosquito-specific toxins that are produced by Bacillus sphaericus (Bs) and Bacillus thuringiensis var israelensis (Bti) are used widely and offer a promising tool due to their efficacy and high safety profile [7, 8]. However, whilst larviciding is a tool that has been used extensively for mosquito control both historically and to-date, the WHO currently recommends its use only as a supplementary intervention in settings in which mosquito larval habitats are few, fixed and findable [7]. This recommendation is due firstly to the limited evidence of epidemiological impact, and secondly to the lack of guidance in which settings it might be effective [7, 9, 10]. As a result, larviciding is not currently funded by maj (...truncated)