Decreased bioefficacy of long-lasting insecticidal nets and the resurgence of malaria in Papua New Guinea

Papua New Guinea (PNG) has the highest malaria transmission outside of Africa. Long-lasting insecticidal nets (LLINs) are believed to have helped to reduce average malaria prevalence in PNG from 15.7% in 2008 to 1% in 2014. Since 2015 malaria indicators in PNG have risen significantly. In the present study, we observed a drastically decreased bioefficacy of unused LLINs with manufacturing dates between 2013 and 2019 collected from villages and LLIN distributors in PNG. Specifically, of the tested n=167 LLINs manufactured between 2013 and 2019 only 16% achieved ≥ 80% 24h-mortality or ≥ 95% 60 min-knockdown in cone bioassays conducted with pyrethroid susceptible Anopheles farauti mosquitoes. In contrast, all (100%, n=25) LLINs with manufacturing dates between 2007 and 2012 achieved ≥ 80% 24h-mortality or ≥ 95% 60 min-knockdown. This difference was extremely statistically significant. We hypothesise that decreased bioefficacy of LLINs has contributed to the malaria resurgence in PNG.