Digitally managed larviciding as a cost-effective intervention for urban malaria: operational lessons from a pilot in São Tomé and Príncipe guided by the Zzapp system

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Abstract

Background

Once a mainstay of malaria elimination operations, larval source management (LSM)—namely, the treatment of mosquito breeding habitats–has been marginalized in Africa in favour of long-lasting insecticidal nets (LLINs) and indoor residual spraying (IRS). However, the development of new technologies, and mosquitoes' growing resistance to insecticides used in LLINs and IRS raise renewed interest in LSM.

Methods

A digitally managed larviciding (DML) operation in three of the seven districts of São Tomé and Príncipe (STP) was launched by the Ministry of Health (MOH) and ZzappMalaria LTD. The operation was guided by the Zzapp system, consisting of a designated GPS-based mobile application and an online dashboard, which facilitates the detection, sampling and treatment of mosquito breeding sites. During the operation, quality assurance (QA) procedures and field management methods were developed and implemented.

Results

12,788 water bodies were located and treated a total of 128,864 times. The reduction impact on mosquito population and on malaria incidence was 74.90% and 52.5%, respectively. The overall cost per person protected (PPP) was US$ 0.86. The cost varied between areas: US$ 0.44 PPP in the urban area, and US$ 1.41 PPP in the rural area. The main cost drivers were labour, transportation and larvicide material.

Conclusion

DML can yield highly cost-effective results, especially in urban areas. Digital tools facilitate standardization of operations, implementation of QA procedures and monitoring of fieldworkers’ performance. Digitally generated spatial data also have the potential to assist integrated vector management (IVM) operations. A randomized controlled trial (RCT) with a larger sample is needed to further substantiate findings.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12936-023-04543-0.

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The statistical interpretation of pilot trials: should significance thresholds be reconsidered?

Ellen Lee, Amy Whitehead, Richard M Jacques … (2014)

Background In an evaluation of a new health technology, a pilot trial may be undertaken prior to a trial that makes a definitive assessment of benefit. The objective of pilot studies is to provide sufficient evidence that a larger definitive trial can be undertaken and, at times, to provide a preliminary assessment of benefit. Methods We describe significance thresholds, confidence intervals and surrogate markers in the context of pilot studies and how Bayesian methods can be used in pilot trials. We use a worked example to illustrate the issues raised. Results We show how significance levels other than the traditional 5% should be considered to provide preliminary evidence for efficacy and how estimation and confidence intervals should be the focus to provide an estimated range of possible treatment effects. We also illustrate how Bayesian methods could also assist in the early assessment of a health technology. Conclusions We recommend that in pilot trials the focus should be on descriptive statistics and estimation, using confidence intervals, rather than formal hypothesis testing and that confidence intervals other than 95% confidence intervals, such as 85% or 75%, be used for the estimation. The confidence interval should then be interpreted with regards to the minimum clinically important difference. We also recommend that Bayesian methods be used to assist in the interpretation of pilot trials. Surrogate endpoints can also be used in pilot trials but they must reliably predict the overall effect on the clinical outcome.

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A new malaria vector in Africa: Predicting the expansion range of Anopheles stephensi and identifying the urban populations at risk

M. Sinka, S. Pironon, N. C. Massey … (2020)

Significance In 2012, an unusual outbreak of malaria occurred in Djibouti City followed by increasingly severe annual outbreaks. Investigations revealed the presence of an Asian mosquito species; Anopheles stephensi, which thrives in urban environments. An. stephensi has since been identified in Ethiopia and Sudan. By combining data for An. stephensi across its full range (Asia, Arabian Peninsula, Horn of Africa) with spatial models that identify the species’ preferred habitat, we provide evidence-based maps predicting the possible African locations where An. stephensi could establish if allowed to spread. Our results suggest over 126 million people in cities across Africa could be at risk. This supports the WHO’s call for targeted An. stephensi control and prioritized surveillance.

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Modelling the impact of vector control interventions on Anopheles gambiae population dynamics

Michael White, Jamie Griffin, Thomas Churcher … (2011)

Background Intensive anti-malaria campaigns targeting the Anopheles population have demonstrated substantial reductions in adult mosquito density. Understanding the population dynamics of Anopheles mosquitoes throughout their whole lifecycle is important to assess the likely impact of vector control interventions alone and in combination as well as to aid the design of novel interventions. Methods An ecological model of Anopheles gambiae sensu lato populations incorporating a rainfall-dependent carrying capacity and density-dependent regulation of mosquito larvae in breeding sites is developed. The model is fitted to adult mosquito catch and rainfall data from 8 villages in the Garki District of Nigeria (the 'Garki Project') using Bayesian Markov Chain Monte Carlo methods and prior estimates of parameters derived from the literature. The model is used to compare the impact of vector control interventions directed against adult mosquito stages - long-lasting insecticide treated nets (LLIN), indoor residual spraying (IRS) - and directed against aquatic mosquito stages, alone and in combination on adult mosquito density. Results A model in which density-dependent regulation occurs in the larval stages via a linear association between larval density and larval death rates provided a good fit to seasonal adult mosquito catches. The effective mosquito reproduction number in the presence of density-dependent regulation is dependent on seasonal rainfall patterns and peaks at the start of the rainy season. In addition to killing adult mosquitoes during the extrinsic incubation period, LLINs and IRS also result in less eggs being oviposited in breeding sites leading to further reductions in adult mosquito density. Combining interventions such as the application of larvicidal or pupacidal agents that target the aquatic stages of the mosquito lifecycle with LLINs or IRS can lead to substantial reductions in adult mosquito density. Conclusions Density-dependent regulation of anopheline larvae in breeding sites ensures robust, stable mosquito populations that can persist in the face of intensive vector control interventions. Selecting combinations of interventions that target different stages in the vector's lifecycle will result in maximum reductions in mosquito density.

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Author and article information

Contributors

Yonatan Fialkoff: yonatan@zzappmalaria.com

Journal

Journal ID (nlm-ta): Malar J

Journal ID (iso-abbrev): Malar J

Title: Malaria Journal

Publisher: BioMed Central (London )

ISSN (Electronic): 1475-2875

Publication date (Electronic): 6 April 2023

Publication date PMC-release: 6 April 2023

Publication date Collection: 2023

Volume: 22

Electronic Location Identifier: 114

Affiliations

[1 ]ZzappMalaria, Menachem Begin 23, Tel Aviv, Israel

[2 ]School of Hygiene and Tropical Medicine, ZzappMalaria, London, Thailand

[3 ]ZzappMalaria, São Tomé, São Tomé and Príncipe

[4 ]Independent researcher, Tel Aviv, Israel

[5 ]Ministry of Health, São Tomé, São Tomé and Príncipe

Article

Publisher ID: 4543

DOI: 10.1186/s12936-023-04543-0

PMC ID: 10080920

PubMed ID: 37024950

SO-VID: e5cee695-8c8d-4882-b790-357c18a3c33b

License:

Open AccessThis article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, 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 changes were made. 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/4.0/. The Creative Commons Public Domain Dedication waiver ( http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data.

History

Date received : 15 November 2022

Date accepted : 23 March 2023

Funding

Funded by: ZzappMalaria

Funded by: Centro Nacional de Endemias

Custom metadata

ScienceOpen disciplines: Infectious disease & Microbiology

Keywords: urban malaria,vector control,larval source management,digitally managed larviciding

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ScienceOpen disciplines: Infectious disease & Microbiology

Keywords: urban malaria, vector control, larval source management, digitally managed larviciding

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Digitally managed larviciding as a cost-effective intervention for urban malaria: operational lessons from a pilot in São Tomé and Príncipe guided by the Zzapp system

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Abstract

Background

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Conclusion

Supplementary Information

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China CDC Weekly: COVID19

Most cited references 20

The statistical interpretation of pilot trials: should significance thresholds be reconsidered?

A new malaria vector in Africa: Predicting the expansion range of Anopheles stephensi and identifying the urban populations at risk

Modelling the impact of vector control interventions on Anopheles gambiae population dynamics

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