Impact of Community-Based Larviciding on the Prevalence of Malaria Infection in Dar es Salaam, Tanzania

Abstract

BackgroundThe use of larval source management is not prioritized by contemporary malaria control programs in sub-Saharan Africa despite historical success. Larviciding, in particular, could be effective in urban areas where transmission is focal and accessibility to Anopheles breeding habitats is generally easier than in rural settings. The objective of this study is to assess the effectiveness of a community-based microbial larviciding intervention to reduce the prevalence of malaria infection in Dar es Salaam, United Republic of Tanzania.Methods and FindingsLarviciding was implemented in 3 out of 15 targeted wards of Dar es Salaam in 2006 after two years of baseline data collection. This intervention was subsequently scaled up to 9 wards a year later, and to all 15 targeted wards in 2008. Continuous randomized cluster sampling of malaria prevalence and socio-demographic characteristics was carried out during 6 survey rounds (2004–2008), which included both cross-sectional and longitudinal data (N = 64,537). Bayesian random effects logistic regression models were used to quantify the effect of the intervention on malaria prevalence at the individual level. Effect size estimates suggest a significant protective effect of the larviciding intervention. After adjustment for confounders, the odds of individuals living in areas treated with larviciding being infected with malaria were 21% lower (Odds Ratio = 0.79; 95% Credible Intervals: 0.66–0.93) than those who lived in areas not treated. The larviciding intervention was most effective during dry seasons and had synergistic effects with other protective measures such as use of insecticide-treated bed nets and house proofing (i.e., complete ceiling or window screens).ConclusionA large-scale community-based larviciding intervention significantly reduced the prevalence of malaria infection in urban Dar es Salaam.

The impact of reduced incidence of malaria and other mosquito-borne diseases on global population

“…Documentation of these benefits may be of interest to contemporary antimalaria programs seeking to avoid negative consequences of large-scale outdoor pesticide spraying (Fillinger and Lindsay, 2011;Gu et al, 2008;Keiser et al, 2005;Maheu-Giroux and Castro, 2013;Nájera et al, 2011;WHO, 2012). 26…”

New approaches for integrated and cost-effective malaria vector control

“…Biological larvicides such as Bacillus thuringiensis israelensis (Bti) are environmentally safe, target species specific in their mode of action, and show no resistances 12 . Within the last decade there has been a large body of evidence generated, showing that Bti based larviciding can bring down malaria vector populations by order of magnitude and significantly reduce malaria prevalence [13][14][15][16] . Recommendations from the WHO currently limit the use of larviciding to urban environments due to the high population density, which provides lower per capita intervention costs compared to less densely populated areas 4 .…”

Joint spatial Bayesian modeling for studies combining longitudinal and cross-sectional data

“…A different cross-sectional formulation, accounting for follow-up data, considering time trend modeled as a first-order autoregressive process, and modeling rainfall with a smooth function where the spline penalty follows a second-order random walk process indicated that the odds of individuals living in areas treated with larviciding being infected with malaria were 21% lower than those who lived in areas not treated; the reduction in the odds was 40% in the dry season. 3 …”

“…2 We chose the UMCP because the program collected both longitudinal and cross-sectional data, with more than 64,000 observations gathered for more than 4 years. Previous evaluations have shown that the intervention significantly reduced the prevalence of malaria infection in intervention areas, 3,4 although none comprehensively addressed the methodological challenges of analyzing a complex dataset such as the UMCP.…”