Title:
Epidemiological Importance of Neglected Malaria Vector Behaviors and Evaluating Novel Tools for Controlling Residual Malaria Transmission in Africa: Individual-Based Modeling Study
Author:
Lin Zhu
Date:
2017
Executive Summary:
Malaria elimination remains a worldwide public health challenge. Residual malaria transmission has been consistently reported even in areas with adequate coverage of the two World Health Organization (WHO) recommended vector control interventions of long-lasting insecticidal nets (LLINs) and indoor residual spraying (IRS). Sugar-feeding and resting are two neglected yet crucial behaviors in malaria vector biology, and the corresponding environmental resources can play a huge role on the vector biology, and consequently on malaria transmission. However, there is little research on these two behaviors. The wide use of the indoor vector control tools has increased insecticide resistance in malaria vectors and the outdoor malaria transmission, which is a major cause for the failure of malaria elimination. Whether indoor vector control alone can achieve malaria elimination is unclear, and there are considerations of incorporating outdoor vector control interventions into the current integrated vector management. Novel tools such as attractive toxic sugar bait (ATSB), which can be used both indoors and outdoors, has been developed in response to the call from WHO. Its efficacy toward controlling malaria vectors has been proved by several field trials, however, more information on its epidemiological impact on malaria transmission and the optimum way to use it is needed. A spatial individual-based model was developed to 1) estimate the impact of environmental sugar sources and resting sites on the survival of malaria vectors and malaria parasite transmission; 2) evaluate the efficacy of ATSB stations and select the optimum number of spatial configuration of the stations for effective malaria control; and 3) evaluate the immediate and long-term effect of outdoor malaria vector control on malaria transmission. Results of study 1 show that small increase in the densities of sugar sources and resting sites resulted in significant increase of survival of malaria vectors and the human biting rates (HBRs). In addition, sugar sources dispersed over the whole area supported the survival of vectors better than being concentrated even near resting sites or houses. Results of study 2 show that ATSB application effectively reduced the density of malaria vectors, HBR and entomological inoculation rate (EIR) in both resource-rich and resource-poor environments. Configurations of dispersed ATSB stations were significantly more effective for vector control in resource-rich environments; but in resource-poor environments, all configurations worked similarly. Reduction of vector density and EIR increased with the increase in numbers of ATSB stations, but it reached a point at which further increase was ineffective. Results of study 3 show that the use of ATSBs as the outdoor intervention in combination with partial LLIN coverage had significantly better immediate and long-term impacts on vector control and EIR reduction than scaling up LLIN coverage to 100%. In conclusion, environmental sugar sources and resting sites play a crucial role in malaria transmission; ATSB stations dispersed over the whole area is recommended for the most effective vector control; and incorporating outdoor vector control into the current indoor interventions is recommended for malaria elimination.
