Vector biting behaviour, community malaria infection risk, and field trial on repellent footwear in southern Mozambique

Abstract

Introduction: Effective control of malaria vectors requires targeting mosquitoes indoors and outdoors. The core interventions currently recommended by the World Health Organization are for large scale deployment of ITNs and IRS. These tools are deployed indoors and have been shown to be effective in protecting against mosquito bites and reducing malaria transmission across many settings. The emergence and spread of resistance to insecticides by mosquito vectors and the shift in vector populations towards those that feed outdoors and early in the evening when people are not protected by LLINs and or IRS, represent a substantial shortfall in protection. To address the outdoor biting and resistant vector populations, innovative interventions with new or existing tools need to be implemented. The efficacy of a repellent-impregnated footwear designed and produced as a controlled slow-release repellent system was tested for efficacy in the field and were contextualized with knowledge, attitude, and practice (KAP), and prevalence surveys, as well as a comprehensive vector survey. Methods: For the mosquito vector survey, human landing catches were conducted over a 9-month period. Morphological and molecular identification, and assays for detection of Plasmodium circumsporozoite protein were performed. A cross-sectional design was used for the KAP survey and prevalence surveys. For the KAP survey, data were collected through questionnaires, while RDTs and microscope examination of finger-prick blood samples were used for population malaria infection rates. A randomized controlled field trial was conducted to determine the efficacy of the repellent-impregnated footwear. The number of collected mosquitoes was compared between groups and the protection efficacy was determined. Results: Seventy-six Anopheles arabiensis and 117 Anopheles funestus s.s. were identified among the 1802 Anopheles mosquitoes collected. One mosquito from each species was found harbouring Plasmodium falciparum circumsporozoite protein. Anopheles arabiensis was biting equally indoors and outdoors and early in the evening (χ2 = 0.48, df = 1, P = 0.53) while Anopheles funestus s.s. was biting more indoors and late at night (χ2 = 31.84, df = 1, P < 0.001). All the infected mosquitoes were collected biting outdoors, suggesting that transmission may be occurring outdoors. The KAP and prevalence surveys revealed that the level of knowledge (89.7%) and practices (89.7%) toward malaria are good, and the attitude (93.7%) is positive among the study participants. The prevalence of malaria was 11.9%. Residing in Conhane neighbourhood (aOR = 16.01, 95% CI 1.87-137.33, P = 0.011) and having a well as the source of water (aOR = 11.82 (95% CI 1.17-119.91, P = 0.037) were identified as risk factors for malaria infection. The repellent-impregnated footwear (mean rank = 214.44) did not show efficacy in reducing Anopheles mosquito bites when compared with the non-impregnated footwear (mean rank = 228.81) (adjusted P = 1). However, the footwear either impregnated or not reduced mosquito bites when compared with a bare foot (mean rank = 287.26) (adjusted P < 0.0001), suggesting that a physical barrier effect is present. Conclusions: This study brought evidence of Plasmodium falciparum infected mosquitoes biting outdoors early in the evening and late at night. This should inform the NMCP to include interventions for malaria vector control outdoors to improve vector control in the village. The KAP and prevalence surveys contributed to reinforcing the importance of the association between living conditions and the higher risk of malaria infection. Improvement in provision of protected sources of water should be considered toward contributing to decreasing risk of malaria infection in Conhane Village. The field trial suggests that the footwear was effective in reducing mosquito bites through a physical barrier effect as opposed to that of a repellent effect. Protection of the lower legs and feet against mosquito bites can be achieved by covering these areas with footwear or clothing. Further studies with repellent-based tools to target the lower limbs should be considered as previous testing of fibres impregnated with repellents were successful.