Abstract
Elimination of visceral leishmaniasis (VL) in Southeast Asia and global control of cutaneous leishmaniasis (CL) and VL are priorities of the World Health Organization (WHO). But is the existing evidence good enough for public health recommendations? This meta-review summarises the available and new evidence for vector control with the aims of establishing what is known about the value of vector control for the control of CL and VL, establishing gaps in knowledge, and particularly focusing on key recommendations for further scientific work. This meta-review follows the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) criteria, including (1) systematic reviews and meta-analyses (SRs/MAs) for (2) vector control methods and strategies and (3) for the control of CL and/or VL. Nine SRs/MAs were included, with different research questions and inclusion/exclusion criteria. The methods analysed for vector control can be broadly classified into (1) indoor residual spraying (IRS); (2) insecticide-treated nets (ITNs; including insecticide-impregnated bednets); (3) insecticide-treated curtains (ITCs; including insecticide-treated house screening); (4) insecticide-treated bedsheets (ITSs) and insecticide-treated fabrics (ITFs; including insecticide-treated clothing) and (5) durable wall lining (treated with insecticides) and other environmental measures to protect the house; (6) control of the reservoir host; and (7) strengthening vector control operations through health education. The existing SRs/MAs include a large variation of different primary studies, even for the same specific research sub-question. Also, the SRs/MAs are outdated, using available information until earlier than 2018 only. Assessing the quality of the SRs/MAs, there is a considerable degree of variation. It is therefore very difficult to summarise the results of the available SRs/MAs, with contradictory results for both vector indices and—if available—human transmission data. Conclusions of this meta-review are that (1) existing SRs/MAs and their results make policy recommendations for evidence-based vector control difficult; (2) further work is needed to establish efficacy and community effectiveness of key vector control methods with specific SRs and MAs (3) including vector and human transmission parameters; and (4) attempting to conclude with recommendations in different transmission scenarios.
Highlights
Elimination of visceral leishmaniasis (VL) in Southeast Asia and global control of cutaneous leishmaniasis (CL) and VL are priorities of the World Health Organizations’ Department of Control of Neglected Tropical Diseases (WHO NTD)
insecticide-treated nets (ITNs) versus no intervention or untreated nets on VL -Two out of the 3 cluster randomised controlled trials (RCTs) in Asia, evaluated the effect of ITNs on vector density -In Bangladesh, there was a substantial reduction in vector density in the ITN areas for 12 months postintervention. -In the multicentre trial from Asia, the overall difference between intervention and control sites was not statistically significant. -One additional cluster RCT in in treated houses in Bihar (India) reported a statistically significant reduction in male P. argentipes in areas with ITNs compared to untreated nets, but no difference in female P. argentipes or other vectors -One cluster RCT evaluated the effect of ITNs on VL in India and Nepal
indoor residual spraying (IRS) versus ITNs, insecticidetreated curtains (ITCs), or insecticide-treated bedsheets (ITSs) on VL -Two cluster RCTs in areas of Asia with VL evaluated the comparative effect of IRS and ITNs -In a trial from Bangladesh, India and Nepal, the pooled data with a followup at 5 months on trapped phlebotomine sand flies in houses showed that IRS was effective with an average sand fly reduction of about 50%, but the ITNs had very little effect. -In one trial from Bangladesh, both interventions were associated with a decrease in sand fly density at 5 months. -A cluster RCT in areas of Brazil with VL, included a comparison of IRS with insecticide-impregnated cotton sheets or blankets
Summary
The effectiveness of vector control for reduction of transmission of both VL and CL is repeatedly under discussion. This has been assessed in numerous reports, including WHO reports, e.g., WHO (2010) [2], and in comprehensive reviews. In this sense, Picado and colleagues (2012) [3] presented a review of studies for VL published in the period 2005 to 2010 on the efficacy of different tools to control Phlebotomus argentipes. The review indicates that “the current indoor residual spraying (IRS) and novel vector control methods mainly insecticide-treated nets (ITN) have low effectiveness for several reasons. In a recent field trial using cluster randomised design, partially unexplored options were tested for sand fly control [4] in order to strengthen the campaign for elimination, the deadline of which was extended from 2015 to 2020 [5]—no definite recommendations are available at this stage
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