A cost-effective, community-based, mosquito-trapping scheme that captures spatial and temporal heterogeneities of malaria transmission in rural Zambia

Abstract

BackgroundMonitoring mosquito population dynamics is essential to guide selection and evaluation of malaria vector control interventions but is typically implemented by mobile, centrally-managed teams who can only visit a limited number of locations frequently enough to capture longitudinal trends. Community-based (CB) mosquito trapping schemes for parallel, continuous monitoring of multiple locations are therefore required that are practical, affordable, effective, and reliable.MethodsA CB surveillance scheme, with a monthly sampling and reporting cycle for capturing malaria vectors, using Centers for Disease Control and Prevention light traps (LT) and Ifakara Tent Traps (ITT), were conducted by trained community health workers (CHW) in 14 clusters of households immediately surrounding health facilities in rural south-east Zambia. At the end of the study, a controlled quality assurance (QA) survey was conducted by a centrally supervised expert team using human landing catch (HLC), LT and ITT to evaluate accuracy of the CB trapping data. Active surveillance of malaria parasite infection rates amongst humans was conducted by CHWs in the same clusters to determine the epidemiological relevance of these CB entomological surveys.ResultsCB-LT and CB-ITT exhibited relative sampling efficiencies of 50 and 7%, respectively, compared with QA surveys using the same traps. However, cost per sampling night was lowest for CB-LT ($13.6), followed closely by CB-ITT ($18.0), both of which were far less expensive than any QA survey (HLC: $138, LT: $289, ITT: $269). Cost per specimen of Anopheles funestus captured was lowest for CB-LT ($5.3), followed by potentially hazardous QA-HLC ($10.5) and then CB-ITT ($28.0), all of which were far more cost-effective than QA-LT ($141) and QA-ITT ($168). Time-trends of malaria diagnostic positivity (DP) followed those of An. funestus density with a one-month lag and the wide range of mean DP across clusters was closely associated with mean densities of An. funestus caught by CB-LT (P < 0.001).ConclusionsCB trapping schemes appear to be far more affordable, epidemiologically relevant and cost-effective than centrally supervised trapping schemes and may well be applicable to enhance intervention trials and even enable routine programmatic monitoring of vector population dynamics on unprecedented national scales.

Characterizing, controlling and eliminating residual malaria transmission

“…Such sites should also overlap both with existing historical entomological study sites for which baseline legacy data is available, and with national platforms for assessing malaria burden through cross-sectional malaria indicator surveys or quality-assured facility-based surveillance.2Establish continuous longitudinal surveillance of mosquito population densities, and the transmission intensity each distinct population mediates, at sites where physiological resistance is monitored, so that the effects of vector control implementation upon seasonal and inter-annual trends can be assessed. Such surveillance platforms are essential to quantify residual transmission and distinguish between the fundamental limitations of an effective vector control strategy delivering incomplete but valuable and sustained impact versus an intervention failure, in the strict sense, which allows vector populations and malaria transmission to rebound (Figure  4) [28, 29, 31]. Such continuous, longitudinal surveys of malaria vector population dynamics have never been applied before at nationally representative scales.…”

“…As such, affordable, practical community- or district-based mosquito trapping schemes, which are nevertheless resourced and managed by centralized national programmes, may need to be developed and evaluated [31, 120]. Given the reliance of scalable trapping schemes, especially those which are community-based, upon widely scattered, field-based personnel who may not always perform adequately [118, 119], it is also essential to establish quality assurance systems in which each of these sentinel sites is regularly and randomly re-surveyed by a centrally coordinated, specialist entomological team using the same trapping methods [31, 120]. Given the diversity of vector species and behaviours across the tropics, setting up such platforms for monitoring mosquito population dynamics may require initial pilot evaluations to select and calibrate suitable trapping methods or validate calibrations from elsewhere.3.Incorporate surveys of vector feeding and resting behaviours (using human landing catch by participants protected with drug chemoprophylaxis [128] and backpack aspirator/resting container/screening barrier sampling tools [129–131], respectively) into the quality assurance surveys described above under point 2, so that the extent to which each important vector species feeds on humans, feeds indoors, or rests indoors, can be quantified.4.Integrate monitoring of relevant human behaviours [16] and ecology, including resource use and livelihoods, vector control coverage and livestock ownership into national malaria surveys and/or entomologic surveillance platforms, so that their contributions to intervention limitations and failures can be assessed.5Where substantial transmission occurs indoors, experimental hut [132–134] facilities should be established at one or two sentinel sites where the most nationally-relevant vector species are abundant, so that the efficacy of vector control interventions can be assessed before and after their introduction [39].…”

Malaria Vector Surveillance and Insecticide Resistance Monitoring and Management

“…Entomological surveillance will also provide information on probable vectors and their potential role in malaria transmission, in addition tobeing pivotal in planning, implementing and evaluating the efficacy and effectiveness of malaria vector control interventions. While community-based entomological monitoring schemes would be cost-effective vector surveillance approaches [17], entomological capacity can be strengthened by partnering with academic and research institutions that could support training of entomologists and laboratory technicians and facilitate data analysis and interpretation [18].…”

IgG antibody response against Anopheles salivary gland proteins in asymptomatic Plasmodium infections in Narino, Colombia

“…EIRs are based on the number of mosquitoes captured and the proportion of mosquitoes infected with Plasmodium [16]. However, estimation of EIR is expensive and may be insufficient in areas of low or seasonal transmission [17,18]. Human Landing Collection (HLC) is currently the only mosquito catching method that can directly measure the biting rates of humanseeking mosquitoes.…”