Linking Anopheles bionomics and human behaviour in the Lao PDR

Area of Science:

• Vector-borne disease control
• Medical entomology
• Public health interventions

Background:

• Laos is working towards malaria elimination by 2030, facing challenges from residual transmission in southern regions.
• Understanding the interplay between long-lasting insecticidal nets (LLINs), vector behavior, human activity, and disease outcomes is crucial for effective malaria control.
• Integrating human behavior observations (HBOs) with entomological and epidemiological data is key to identifying protection gaps and informing national malaria programs.

Purpose of the Study:

• To assess the effectiveness of LLINs in relation to human and Anopheles mosquito behavior in Laos.
• To identify gaps in protection against malaria vectors, particularly in outdoor and early evening settings.
• To inform targeted malaria control strategies by integrating entomological and human behavior data.

Main Methods:

• Conducted entomological surveillance of Anopheles mosquitoes and HBOs across villages, cultivation sites, and forests during rainy and dry seasons.
• Collected mosquitoes using indoor and outdoor human landing catches (HLCs) and identified species morphologically.
• Adjusted human biting rates (HBR) with HBO data to quantify spatial-temporal protection and identify gaps, also assessing Anopheles indoor resting rates.

Main Results:

• Collected 1012 Anopheles mosquitoes across 12 species, with higher numbers in cultivation sites than villages or forests.
• Human behavior-adjusted biting rates indicated highest exposure outdoors, especially between 18:00-22:00 and 03:00-06:00 in villages.
• LLINs prevented 42% of total Anopheles bites and 83% of indoor bites in villages, but only reduced outdoor exposure by 26% at cultivation sites.

Conclusions:

• Peridomestic human and Anopheles behaviors in Laos create significant outdoor protection gaps, particularly in the early evening.
• High LLIN coverage is vital for reducing indoor bites in villages, while indoor residual spraying (IRS) may have limited impact.
• Integrating HBOs with entomological data provides critical insights into residual malaria transmission, highlighting the need for innovative, targeted interventions for outdoor and early evening settings.