Large-scale field trial of attractive toxic sugar baits (ATSB) for the control of malaria vector mosquitoes in Mali, West Africa

Abstract

Background: The aim of this field trial was to evaluate the efficacy of attractive toxic sugar baits (ATSB) in Mali, where sustained malaria transmission occurs despite the use of long-lasting insecticidal nets (LLINs). ATSB bait stations were deployed in seven of 14 similar study villages, where LLINs were already in widespread use. The combined use of ATSB and LLINs was tested to see if it would substantially reduce parasite transmission by Anopheles gambiae sensu lato beyond use of LLINs alone. Methods: A 2-day field experiment was conducted to determine the number of mosquitoes feeding on natural sugar versus those feeding on bait stations containing attractive sugar bait without toxin (ASB)-but with food dye. This was done each month in seven random villages from April to December 2016. In the following year, in seven treatment villages from May to December 2017, two ATSB bait stations containing the insecticide dinotefuran were placed on the outer walls of each building. Vector population density was evaluated monthly by CDC UV light traps, malaise traps, pyrethrum spray (PSCs) and human landing catches (HLCs). Female samples of the catch were tested for age by examination of the ovarioles in dissected ovaries and identification of Plasmodium falciparum sporozoite infection by ELISA. Entomological inoculation rates (EIR) were calculated, and reductions between treated and untreated villages were determined. Results: In the 2-day experiment with ASB each month, there was a lower number of male and female mosquitoes feeding on the natural sugar sources than on the ASB. ATSB deployment reduced CDC-UV trap female catches in September, when catches were highest, were by 57.4% compared to catches in control sites. Similarly, malaise trap catches showed a 44.3% reduction of females in August and PSC catches of females were reduced by 48.7% in September. Reductions of females in HLCs were lower by 19.8% indoors and 26.3% outdoors in September. The high reduction seen in the rainy season was similar for males and reductions in population density for both males and females were > 70% during the dry season. Reductions of females with ≥ 3 gonotrophic cycles were recorded every month amounting to 97.1% in October and 100.0% in December. Reductions in monthly EIRs ranged from 77.76

Estimating the potential impact of Attractive Targeted Sugar Baits (ATSBs) as a new vector control tool for Plasmodium falciparum malaria

“…Furthermore, we predict more substantial reductions in clinical incidence than obtained from the equilibrium relationships; this is in part due to the bene t from higher levels of pre-existing immunity that we expect to decay over subsequent years if the intervention is maintained. However, the study also showed a lower impact on the HLC endpoint underlying the EIR estimates compared to the CDC trap data used for our dynamic model projections [16] . Figure 5C-D shows the predicted reductions in parasite prevalence and clinical incidence due to ATSB for a range of excess mortality values (on the x-axis) and baseline transmission levels (on the y-axis).…”

“…A cluster-randomised entomological study [16] was undertaken in 14 villages in southern Mali between April 2016 and December 2017.…”

“…This represents additional baseline mortality above the value of µ NAT present in both control and intervention villages due to non-ATSB vector control interventions. Long-lasting insecticide-treated nets were present in the study region at high coverage [16], but a gure for the additional baseline mortality cannot be estimated accurately as the e cacy (which can vary depending on usage patterns and insecticide resistance) is not known. The value obtained where µ BASE = µ NAT is used in the remainder of this paper as a conservative estimate of the actual excess mortality and an effective value applicable to calculations where LLINs are not incorporated.…”

“…We combine data from the rst cluster-randomised entomological study [16] of ATSBs in Africa with mathematical modelling to explore the potential utility of this new tool to reduce P.falciparum malaria prevalence and clinical incidence in humans. The cluster-randomised entomological study was undertaken in southern Mali between April 2016 and December 2017, with the e cacy measured through oneday tests using non-toxic stained bait (to estimate the bait feeding rate), monthly mosquito catches in intervention and control villages and monthly estimates of the entomological inoculation rate (EIR) -the number of infective bites received per person per unit time (to estimate onward infectivity to humans).…”

A Cohort Study To Identify Risk Factors For Malaria In Burkinabe Children: Implications For Other High Burden High Impact Countries

“…In the study site an estimated 85% of exposure to malaria vector bites can be prevented by use of ITNs from 22.00 h to 05.00 h but early evening biting outdoors and sporozoite rates of 3.3%, mean that residents are still exposed to ~ 32 infectious bites per person per year even with high ITN compliance (Sanou A., in prep). Early evening biting outdoors when people are active in the peridomestic environment is common across Africa (46), and highlights the need for vector control tools that can protect outdoors, such as insecticide-treated 'eave ribbons', attractive targeted sugar baits or larval source management (47)(48)(49).…”