Disposal practices of long-lasting insecticidal nets, toxicity of the discarded nets and its potential implication on the development of pyrethroid resistance in Anopheles gambiae in Southern Ghana

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BACKGROUND: Long-lasting insecticidal nets (LLINs) are central to malaria control, yet their management after loss of intended use remains poorly regulated in many African countries. Improper disposal or repurposing of LLINs may result in various environmental issues including release of insecticide residues and unintended exposure of malaria vectors. This study assessed the disposal practices in urban and rural households and evaluated the toxic effect of discarded LLINs against the malaria vector, Anopheles gambiae. METHODS: We employed a mixed-methods approach comprising (i) a cross-sectional household survey to characterize LLIN ownership, use, and disposal practices in selected urban and rural communities in Ghana, and (ii) laboratory bioassays to evaluate the biological activity of insecticide residues from repurposed LLINs against field populations of Anopheles gambiae. Larval bioassays were conducted using water in which pieces of netting from LLIN had been soaked for short-term (1 day) and prolonged (7 days) exposure periods, while adult toxicity was assessed using cone bioassays. Susceptibility of the mosquito population to deltamethrin was also determined. RESULTS: Repurposing of retired LLINs for agricultural fencing was common in both rural and urban settings (33%), alongside disposal by discarding in open environments. Water used to soak repurposed LLINs caused significant larval mortality and strong inhibition of pupation with survival probability of 15.1% after eight days, whereas adult exposure to the same nets resulted in negligible mortality. CONCLUSION: Repurposed LLINs retain biologically active insecticide residues capable of exerting strong sublethal effects on malaria vector larvae. Although this does not constitute direct evidence of resistance evolution, such exposure may contribute to selection pressures that maintain or amplify existing insecticide resistance. These findings highlight the need for clear national guidelines and community education on LLINs end-of-life management.

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