Large-scale intermittent larviciding intervention and associations with key malaria epidemiological parameters in Tanga Region, Tanzania

(2025) 24:350 Kailembo et al. Malaria Journal https://doi.org/10.1186/s12936-025-05548-7 Malaria Journal Open Access RESEARCH Large‑scale intermittent larviciding intervention and associations with key malaria epidemiological parameters in Tanga Region, Tanzania Denis Kailembo1,2*, Tegemeo Gavana1,2,3, Elizabeth Kasagama1,2, Jubilate Bernard4, Fabrizio Molteni1,2, Noela Kisoka1,2, Best Yoram5, Stella Kajange5, Samwel Lazaro4, Charles Dismas4, Amanda Ross1,2, Prosper Chaki3 and Christian Lengeler1,2 Abstract Background Malaria remains one of the major public health problems both globally and in Tanzania. In addition to existing malaria control interventions, the country plans to introduce larviciding in its efforts towards malaria control and elimination. To guide a possible national upscaling of the intervention, a pilot larviciding study using biolarvicides produced in-country was implemented and evaluated to generate a body of evidence on operations and the impact of the intervention. The current manuscript reports on the association between larviciding and three major malaria epidemiological parameters. Methods Larviciding was conducted in three councils in Tanga Region in the North-East of the country and covered a population of over 1.1 million. The councils represented different malaria risk strata: high, moderate, and low. Larviciding was conducted between June 2022 and April 2024 through a community-based approach using existing local government structures. Larviciding was applied intermittently in the intervention councils to all identified breeding habitats for three rounds per year, based on the local rainfall seasons. Both Bacillus thuringiensis var. israelensis and Bacillus sphaericus were used and each round comprised of 8 consecutive weeks of biolarvicide application. Epidemiological data, including malaria incidence, laboratory malaria test positivity rate and antenatal malaria test positivity rate, were collected from routine health facility data. Each intervention council was paired with multiple control councils based on malaria risk and rainfall patterns, allowing a controlled before-after study design. The association between larviciding and malaria incidence was assessed using negative binomial regression while logistic regression was used for the other epidemiological outcomes. Results The intervention did not have a significant association with the incidence of reported clinical malaria among all age-groups. The estimated incidence rate ratio (IRR) was 1.16 (95% CI 0.98; 1.37) in the high, 0.86 (95% CI 0.72; 1.02) in the moderate, and 0.96 (95% CI 0.76; 1.22) in the low stratum. Similar results were observed across other epidemiological parameters. There was a slight tendency for estimates in the moderate and low strata to be in the direction of a reduction. *Correspondence: Denis Kailembo Full list of author information is available at the end of the article © The Author(s) 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/. Kailembo et al. Malaria Journal (2025) 24:350 Page 2 of 13 Conclusion Under the current design of intermittent larviciding application, there was no strong evidence of an association between larviciding and malaria epidemiological indicators. More studies considering continuous year-round implementation and randomizing a large number of clusters could generate further evidence on the contribution of larviciding to malaria control in similar transmission settings. Keywords Malaria, Larviciding, Bacillus thuringiensis var. israelensis, Bacillus sphaericus, Malaria control, Tanzania Mainland Background Malaria remains one of the major global public health problems. The World Health Organization (WHO) estimated that there were 263 million malaria cases worldwide in 2023 [1], of which around 246 million (94%) were from the WHO African Region. In Tanzania, malaria is a major cause of morbidity and mortality, with over three million clinical cases reported through routine health facilities in 2024 [2]. Insecticide-treated mosquito nets (ITNs), and indoor residual spraying (IRS) have been shown to have a major impact in reducing the burden of malaria [3, 4]. Following large advances achieved by scaling up interventions between 2000 and 2015, reductions in the malaria burden have stagnated over the past decade [1]. In Tanzania, the malaria prevalence among children under 5 years of age remained relatively unchanged between 2017 and 2022 at 7.3% [5] and 8.1% [6], respectively. Emerging resistance to insecticides used in ITNs and IRS has been documented [7–14], as well as concerns about the durability of standard ITNs [15–18]. Moreover, changes in vector behavior from indoor to outdoor biting and resting have also been reported [19–22]. These challenges underscore the urgent need for additional preventive measures. Larval Source Management (LSM) is one of the supplementary malaria control measures recommended by the WHO. It is defined as the management of potential mosquito breeding habitats to prevent the maturation of mosquito larvae to the adult stage [23]. LSM can be implemented through environmental management (i.e. habitat modification and habitat manipulation), biological control, and larviciding. To date, LSM implementation in sub-Saharan Africa (SSA) has been primarily through larviciding. The WHO does not currently recommend the implementation of larviciding in all areas, but only where breeding habitats are few, fixed and findable [23]. The impact of LSM on malaria control through environmental management and larviciding, conducted either alone or in combination, was assessed in a 2013 Cochrane Systematic Review, whereby the findings showed mixed results [24]. A more recent Cochrane Systematic Review, in 2019 which included four studies assessed only the impact of larviciding on malaria control and also found mixed results [25]. While one study in SriLanka used insect growth regulators, the studies in Tanzania, Kenya and The Gambia used microbial larv (...truncated)