Outdoor biting by malaria vectors: what are the options for intervention?

A significant portion of malaria transmission occurs outdoors, especially in the Asia-Pacific region. Current capacity to control such outdoor biting and resting mosquitoes is inadequate, and an expanded range of tools to deploy in outdoor situations is required. This paper explores the range of options available, their current status and potential for effective implementation.

A literature review of the status of classes of interventions to reduce outdoor biting was conducted, including: attractive targeted sugar baits, endectocides, outdoor residual spraying, fogging, mass trapping, genetic modification techniques (3 categories), larval source management, repellents (4 categories), raised platforms, and zooprophylaxy. While not product class-specific, social engagement and behaviour change, and the more encompassing integrated vector management framework are also described as enabling strategies. The product-specific interventions were chosen if they were the subject of multiple peer-reviewed papers, and have some evidence of effectiveness. The status and potential for effective implementation are provided for each.

There are many vector control interventions that contribute to control populations of outdoor biting mosquitoes or lead to a reduction of transmission potential. Larval Source Management is effective in some contexts but not others, and has WHO endorsement as a Supplemental Method for vector control. Spatial emanators/repellents have recently received WHO recommendation for indoor application, but may also be effective in the peridomestic space and temporary shelters. Topical repellents are effective for short-term exposure but less for long-term community protection. Endectocides offer potential in focal locations, especially as they bring benefits in helminth control for domestic animals and has good community acceptance, Gene drive holds the possibility for incisive vector control but remains a longer-term vision.

There is no universally applicable tool to prevent outdoor transmission. Each has its own utility, depending on local context. The best approach is integrating complementary techniques and community engagement to provide a broad shield of response against outdoor biting mosquitoes. As the WHO Integrated Vector Management framework recommends, it is through a broad approach of combined interventions, along with community engagement, improved data for decision-making, cross-sectoral collaboration and capacity building that can more effectively address outdoor biting of malaria vectors.