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

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.

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.

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.

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.