Abstract / Summary
In Burundi, malaria due to Plasmodium falciparum is the leading cause of outpatient visit and hospital mortality. Anopheles gambiae s.l. and An. funestus s.l. are the primary malaria-transmitting vectors. The World Health Organization (WHO) recommends large-scale insecticide-treated nets (ITNs) distribution and/or indoor residual spraying (IRS) as core vector control interventions for malaria. This study aimed to assess the trend of entomological and epidemiological parameters over 5 years of combined IRS and standard ITNs interventions in Kiremba health district, northern Burundi. Over the period 2017–2021, surveillance data on malaria vector species composition and distribution, human biting rate (HBR), entomological inoculation rate (EIR), indoor resting density, malaria cases, and test positivity rate were collected from the Kiremba health district. Changes in the composition of Anopheles species were analyzed using Pearson's chi-square and multivariate analysis of entomological and epidemiological indicators ‘means. Additionally, malaria vector abundance and infectivity trends were assessed. To evaluate any changes in HBR, indoor residual density, and EIR, a linear regression model was applied. In contrast, negative binomial regression analysis was conducted to examine whether malaria cases and test positivity rates varied. Using the Pearson correlation coefficient, the relationship between malaria cases and EIR was examined. Main findings showed that An. gambiae s.l. was the predominant vector species and responsible for most of the transmission in Kiremba. However, the relative abundance of malaria vectors shifted over time: An. funestus s.l. was the second most abundant species in 2017 but was surpassed by An. ziemanni from 2018 to 2020, before regaining its position in 2021. The HBR of An. gambiae s.l. was similar indoor and outdoor in 2017 (p = 0.27), 2018 (p = 0.46), and 2019 (p = 0.16) but higher outdoor biting compared to indoors in 2020 with 0.23 bites/person/night (b/p/n) outdoors vs 0.17 bp/ indoor (p = 0.04) and 2021 (0.15 b/p/n) outdoor vs 0.08 b/p/n indoor; p = 0.001. Compared to 2017, there was no significant reduction in EIR over the study period (p > 0.05). Malaria cases remained high but compared to 2017, a reduction of 28% (IRR = 0.72, p = 0.04) and 26% (IRR = 0.736, p = 0.05) was observed in 2018 and 2020, respectively. The test positivity rate decreased by 22% (IRR = 0.78, p = 0.01) in 2018; however, it remained above 50% throughout the study period, indicating persistently high malaria transmission. Combining IRS, and standard ITNs in Kiremba led to a change in vector species composition and the biting behavior of An. gambiae s.l. to bite more outdoors than indoors. Although temporary reduction in malaria cases (28% in 2018;26% in 2020) and test positivity rate (22% in 2018) were observed, the biting rates and malaria transmission intensity as determined from EIR remained high across the years.