Abstract
BACKGROUND: Insecticide-treated nets (ITNs) remain a key intervention in malaria prevention. However, their protective effectiveness may decline with physical deterioration, even when usage remains high. This study assessed the impact of ITN physical integrity on children's exposure to Anopheles mosquito bites over a three-year period in Mali, using gSG6-P1 biomarker as an innovative immuno-epidemiological indicator of human exposure. METHODS: A three-year prospective cohort study was conducted from 2018, 2019, and 2020 in two rural health districts of Mali: Kéniéba using Yorkool(®) ITNs and Kita using PermaNet(®) 2.0 ITNs. A total of 586 children under five years old were enrolled and followed annually across 30 villages randomly selected into the two districts. Household surveys captured ITN ownership, usage patterns, and net condition. Net physical integrity was evaluated using proportional hole index (pHI). Blood samples were collected each year and analysed for anti-gSG6-P1 IgG levels, expressed as ΔOD. Net condition and specific IgG levels were analysed across time points and stratified by site and ITNs type. RESULTS: ITN usage remained high (> 75%) across all survey years, but the proportion of serviceable nets declined significantly, particularly for Yorkool(®) (49% at 36 months versus 78% for PermaNet(®) 2.0). Median anti-gSG6-P1 IgG levels increased concurrently, indicating rising exposure to Anopheles bites as net integrity deteriorated. Children sleeping under Yorkool(®) nets showed higher specific IgG levels than those using PermaNet(®) 2.0, suggesting reduced protective performance of Yorkool(®) over time. CONCLUSION: This study demonstrates that ITN effectiveness decreases as physical deterioration advances, even when usage is maintained. Monitoring net integrity through the gSG6-P1 biomarker provides an innovative, field-adapted approach to anticipate ITN protection failures and to support evidence-based decision-making in malaria control programmes.