Integration of vector and human behavior in residual malaria in rural communities in the Peruvian Amazon

Malaria persists as a leading cause of morbidity in the Amazon Basin, where the Loreto region of Peru contributes over 90% of the national burden. Despite widespread deployment of long-lasting insecticidal nets (LLINs) and indoor residual spraying (IRS) under Peru's Malaria Elimination Plan 2022-2030, residual transmission continues in rural riverine communities. This transmission is driven by the interplay between vector ecology and human behavior. This study quantified residual human exposure to Nyssorhynchus darlingi by integrating hourly entomological indices with real-time human behavioral data across two seasons in three communities in Mazán, Loreto.

Entomological (HLC) and epidemiological (HBS) data were collected during the wet and dry seasons of 2022. Plasmodium infections were detected in 619 participants by microscopy and qPCR. Molecular surveillance revealed a 13% infection prevalence over seven times higher than routine microscopy (2%) indicating a substantial submicroscopic reservoir. Infection burden was heterogeneous, with Gamitanacocha showing the highest prevalence (33%). LLIN usage was high (>97%), yet nets prevented only 63.3%-80.3% of potential mosquito bites. Residual exposure occurred mainly indoors during early evening (18:00-21:00) while individuals were awake and unprotected, particularly in the dry season when domestic routines coincided with peak vector biting. Outdoor exposure increased during the wet season due to evening recreational activities. Multivariate analysis identified age as the only significant predictor of infection (p < 0.05), with individuals over five years showing consistently higher odds of infection than children under five (OR range: 3.62-5.46).

A critical protection gap exists during early evening and dawn, when human activity overlaps with peak vectors biting outside the protection of bed nets. The high submicroscopic burden and persistent indoor exposure while awake demonstrate that current interventions are insufficient for elimination. These findings highlight that Loreto's elimination strategies must complement intradomiciliary tools with peri-domestic and behavioral interventions-such as full house screening and spatial repellents-specifically targeting the exposure windows identified here.