Integrated Vector Management – generation and use of evidence for more effective vector control

Abstract

Vector-borne diseases (VBD) such as malaria, dengue and leishmaniasis have a major public health impact primarily in low and middle income countries in the tropics. Vector control methods including long-lasting insecticidal nets and indoor residual spraying contribute substantially to control of VBDs, particularly malaria. However, progress is being hampered by a number of factors including a lack of human, infrastructural and financial resources, and is threatened by the development of insecticide resistance. The World Health Organization (WHO) strongly advocates the use of Integrated Vector Management (IVM), a policy which has the potential to overcome many of the challenges facing vector control. IVM calls for evidence-based and adaptive use of vector control tools and involvement of multiple sectors to control VBDs. This thesis brings together work on the theme of IVM and the generation and use of evidence for better vector control programming. Specifically I ask how do we develop high quality evidence to improve the effectiveness of vector control?
The writer has been a principal author of a recently published WHO Toolkit for IVM in sub-Saharan Africa (Volume II of this thesis). This toolkit for vector control programme managers builds on previous WHO guidance by providing practical detail on how to plan, implement, and monitor and evaluate an IVM programme. In order to provide guidance on choice of vector control interventions in the IVM toolkit, it was necessary to systematically review the evidence from field trials of vector control tools. Two systematic reviews are presented evaluating the efficacy of insecticide-treated nets, curtains and screening against non-malaria VBDs, and the efficacy of topical repellents against malaria. These found that: i) insecticide-treated materials in the home (nets, curtains and screening) are protective against cutaneous leishmaniasis and may be protective against dengue and Japanese encephalitis, ii) topical repellents are not protective against falciparum or vivax malaria in endemic populations. Systematic reviews revealed a paucity of well-conducted efficacy studies of vector control interventions which hinders evidence-based policy-making. A critical analysis of vector control study design and conduct is presented. This analysis identified common failings with vector control trials including a lack of randomisation and blinding, poor choice of outcome measures, lack of replication, no sample size calculations and contamination between clusters in cluster-randomised trials. Many of these failings could be easily rectified to produce better quality evidence and prevent waste in research.
As well as evidence-based policy making on vector control interventions, IVM calls for use of evidence throughout the lifetime of the programme through entomological and epidemiological surveillance and monitoring and evaluation to choose and target interventions, measure their effectiveness and adapt the programme over time. One entomological parameter which should be measured is insecticide resistance. A study of the spatial and temporal pattern of knockdown resistance (kdr) resistance in Anopheles gambiae s.l. in a setting of high vector control use in the Upper River Region of The Gambia is presented which found that: i) An. arabiensis was the most common member of the species complex, ii) the odds of kdr were 24 times higher in An. gambiae s.s. in villages with both IRS and LLINs and 14 times higher in villages with LLINs alone, iii) the kdr mutation was more common in mosquitoes in the second year of the study and with increasing distance from the river.
The result of this work is the IVM Toolkit for sub-Saharan Africa. IVM provides a logical framework to think through vector control and advocates for a more locally tailored and adaptive approach which engages partners within and beyond the health sector. Compared to current vector control, IVM has the potential to be more effective (through evidence-based use of interventions), cost-effective (through implementation of cost effective interventions and sharing of resources across sectors), sustainable (through engagement and mobilisation of communities and the non-health sector) and ecologically sound (through the use of non-insecticide-based tools). However, there are a number of challenges to utilisation of IVM. While this thesis outlines the theoretical framework for IVM, it does not test its use by programmes, and in fact there are few good examples of IVM in practice available. Policies and organisational structures of vector control programmes are currently not in support of IVM. Lack of resources (infrastructural, human and financial) hampers implementation of this more knowledge-intensive and adaptive approach to vector control. Deeply engrained silos and lack of political support may impede partnership working within and across sectors. An increased focus on vector control in the light of the recent Zika virus disease outbreak and high-level policy changes at WHO including development of the forthcoming Global Vector Control Response should galvanise support for vector control and reorientation of programmes towards an IVM approach. IVM can be implemented if there is additional and sustained financing for vector control, an investment in human resources and infrastructure, and more commitment to working across sectors. It is important to grasp this opportunity in order to exploit fully the potential of vector control to control and eliminate VBDs in the future.