Identifying gaps in protection from malaria vector biting in rural Cambodia using an entomological assessment and human behaviour observations
Authors: McIver David J. , Vajda Elodie A. , Doum Dyna , Daniel Nicholas W. , Quan Molly , Lovin Diane D. , Cunningham Joanne M. , Sovannaroth Siv , Tatarsky Allison , Lobo Neil F. 
Published: November 2024

Background:
Forest-exposed populations make up the last significant, and most difficult to access, high-risk populations for malaria in Cambodia. Though long-lasting insecticide treated nets (LLINs) and/or hammock nets (LLIHNs) are usually available, continued malaria transmission indicates that gaps in protection remain. This study was part of a larger research program, Project BITE, and aimed to identify gaps in protection among forest-exposed individuals in P. falciparum hotspots in two provinces in Cambodia, using a combination of entomological assessments and human behaviour observations (HBOs).
Methods:
Anopheles bionomic traits were characterized using Human Landing Catches (HLCs) in a village setting in Mondulkiri province, and in both village and forest settings in Kampong Speu province, Cambodia. Mosquitoes were collected over a 14-hour period from 17h00–07h00 over a total of 540 collection nights. Human behaviour characterization centered on observing people and their activities proximate to HLC sites throughout the night (i.e., human behaviours, or HBOs) and documenting whether they were using an LLIN/LLIHN or any of the novel bite prevention tools provided as part of Project BITE, which included a volatile pyrethroid spatial repellent (VPSR), topical repellent (TR), and insecticide treated clothing (ITC). Data on mosquito landing pressure and human behaviours were integrated to generate the HBO-adjusted Human Landing Rate (HBO-adjusted HLR).
Results:
A total of 5,985 Anopheles mosquitoes were collected in Mondulkiri and Kampong Speu provinces, with 608 (10%) identified molecularly to species-level. Seventeen Anopheles species were identified, including a likely novel species from the Leucosphyrus Subgroup, which was the predominant species characterized. When considering the times when mosquitoes were host seeking, and how and when people used bed nets, the HBO-adjusted HLR was found to be greatest during the early evening hours, when people were outdoors awake, followed by when people were sleeping indoors without a net. Relatively few people were observed using, or correctly using, the new bite prevention tools intended for protection in the forest.
Conclusion:
This study demonstrates the importance of understanding spatial and temporal human exposure to mosquito bites, in the presence of proven vector control tools (LLINs, LLIHNs) and bite prevention tools (VPSRs, ITCs, and TRs). To help achieve malaria elimination, human behaviour data on intervention use and awake and sleep patterns should be evaluated and integrated with entomological data towards identifying and quantifying protection conferred by current interventions, as well as remaining gaps in protection. Furthermore, appropriate and targeted social and behavioral change communication tools are needed to reinforce continued and correct use of newly introduced tools. This information supports the selection of appropriate interventions, which supplement rather than replace existing tools, to target existing gaps in protection.