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

AbstractBackgroundPapua New Guinea (PNG) has the highest malaria transmission outside of Africa and long-lasting insecticidal nets (LLINs) are the only vector-control tool distributed country-wide. LLINs were introduced into PNG in about 2006 and have been attributed to have had a huge impact on malaria transmission, with reductions in observed average malaria prevalence from 15.7% (2008) to 1% (2014). However, since 2015 malaria indicators in PNG have risen significantly. Similar trends have been observed in several African nations. In the present study, we observed a drastic reduction in bioefficacy of LLINs collected both from households as used nets and prior to use in original, unopened packaging. We hypothesise that decreased bioefficacy of LLIN is a major contributor to the observed malaria resurgence in PNG and possibly in other parts of the world.MethodsNew LLINs in original and unopened packaging (n=192) manufactured between 2007-2019 were collected in 15 PNG provinces. Used LLIN (n=40) manufactured between 2008 and 2017 were collected in 2 provinces. LLIN were subjected to standard WHO cone bioassays using fully susceptible An. farauti mosquitoes. A subset of LLIN was re-tested using fully susceptible An. gambiae G3 mosquitoes in order to ensure reproducibility of results.ResultsOnly 7% (95% CI 4-12%) of new LLINs manufactured between 2013-2019 exhibited 100% mortality. However, 84% (95%CI: 65-84%) new nets manufactured in 2012 or before exhibited 100% mortality. Only 29 % of used LLIN less than 3 years old exhibited > 80% 24h-mortality. Results obtained in tests using An. farauti corresponded well with confirmatory tests conducted using An. gambiae.DiscussionBioefficacy of LLIN in PNG appears to have been highly variable since 2013, with few nets manufactured since 2013 meeting WHO standards. This time-frame coincides with malaria resurgence in the country. These results may have ramifications for LLIN-based malaria control that go beyond the local PNG scenario.