Incidence of Malaria among Mosquito Collectors Conducting Human Landing Catches in Western Kenya

Abstract

Abstract. The human landing catch (HLC) has long been the gold standard for estimating malaria transmission by mosquitoes, but has come under scrutiny because of ethical concerns of exposing collectors to infectious bites. We estimated the incidence of Plasmodium falciparum malaria infection in a cohort of 152 persons conducting HLCs and compared it with that of 147 non-collectors in western Kenya. Participants were presumptively cleared of malaria with Coartem™ (artemether-lumefantrine) and tested for malaria every 2 weeks for 12 weeks. The HLC collections were conducted four nights per week for six weeks. Collectors were provided chemoprophylaxis with Malarone™ (atovaquoneproguanil) during the six weeks of HLC activities and one week after HLC activities were completed. The incidence of malaria was 96.6% lower in collectors than in non-collectors (hazard ratio = 0.034, P 0.0001). Therefore, with proper prophylaxis, concern about increased risk of malaria among collectors should not be an impediment to conducting HLC studies.

Reemergence of Anopheles funestus as a Vector of Plasmodium falciparum in Western Kenya after Long-Term Implementation of Insecticide-Treated Bed Nets

“…Numerous studies of malaria vectors have been conducted here since the 1970s, and the region has been described in detail. 20,21 Malaria is holoendemic in Asembo and is caused chiefly by Plasmodium falciparum. Rainfall occurs year-round but is seasonally bimodal, with peaks occurring from March through May and in November and December.…”

“…Nationwide, ITNs became available at partially subsidized rates through the retail sector in 2002, and at heavily subsidized rates through health clinics in 2004. 23 21 Local adult men were trained as collectors and organized into 38 teams of four persons from two neighboring villages with the exception of one team that consisted of only two collectors. Each team rotated among four collection sites, sampling for 4 nights every week.…”

Entomological surveillance of behavioural resilience and resistance in residual malaria vector populations

“…Furthermore, measurements of human biting rates both indoors and outdoors throughout the night need to be combined with surveys of human behaviour to estimate the proportion of human-vector contact which occurs indoors [4,38]. While alternative methods for quantifying mosquito-human interactions indoors and outdoors are not yet ready to replace human landing catches [75], recent evidence suggests that participants protected with drug prophylaxis are actually safer from malaria than they would be asleep at home [76]. Feeding upon non-human hosts limits malaria transmission [31] but also, creates large gaps in biological coverage of human-targeted interventions like ITNs and IRS [32].…”

“…Incorporate surveys of vector feeding and resting behaviours, using human landing catch by participants protected with drug chemoprophylaxis [76] and backpack aspirator/screening barrier sampling tools [84,85], respectively, into these quality assurance surveys to quantify the extent to which each important vector species feeds on humans, feeds indoors or rests indoors.…”

Characterizing, controlling and eliminating residual malaria transmission

“…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]. …”