Effect of Short-Term Heating on Bioefficacy of Deltamethrin-Coated Long-Lasting Insecticidal Nets

Anetul

et al. 2022

Preprint

Self Cite

Introduction: Long lasting insecticidal nets (LLINs) play a key role in reducing malaria transmission in endemic countries. Previously, we demonstrated a substantial decrease in the bioefficacy of LLINs for malaria prevention delivered to Papua New Guinea (PNG) between 2013 and 2019. This coincided with a rise in malaria cases in the country. The present study was aimed at determining the underlying cause of the observed reduced bioefficacy of these LLINs. In particular, we tested the hypothesis that a change in the coating formulation of the respective LLIN product was the cause for the observed reduction in bioefficacy, and had led to completely altered product properties and performance. Methods A set of PermaNet® 2.0 LLIN samples (n = 12) manufactured between 2007 and 2019 was subjected to combustion ion chromatography in order to understand the chemistry of the LLIN polymer coating formulation. In addition, World Health Organization (WHO) LLIN wash tests and cone bioassays were conducted to further characterize the change in product performance that occurred between 2012 and 2013. Results High polymer fluorine content (3 to 4 g/kg) was measured in PermaNet® 2.0 manufactured up to 2012, whereas nets which were manufactured after 2012 did not contain polymer fluorine indicating a coating formulation change from polyfluorocarbon (PFC) to a non-PFC formulation. The coating formulation change as part of the manufacturing process thus directly resulted in the observed reduction in bioefficacy. In addition, the manufacturing change impacted wash resistance leading to a faster reduction in 24h mosquito mortality in the non-PFC coated product. Conclusion A change in coating formulation of PermaNet® 2.0 resulted in reduced product performance in PNG. Post-2012 PermaNet® 2.0 LLINs should not be considered to be the same product as PermaNet® 2.0 LLINs produced prior to and in 2012. Coating formulation changes should be validated not to impact LLIN product performance.

Section: Introductionmentioning

confidence: 67%

Coating formulation change leads to inferior bioefficacy of long-lasting insecticidal nets in Papua New Guinea

Anetul

et al. 2022

Preprint

Self Cite

“…Also, older nets that had been stored for much longer and exhibited 100% kill rate had, on average, slightly lower insecticide content which we attributed to natural decay over many years of storage 7 . In addition, we showed that short-term heating of the LLINs in question increased their potency to kill mosquitoes (rather than to decrease it), which we attributed to a heat-facilitated migration of the insecticide from inside the coating to the net surface 8,9 .…”

Section: Main Textmentioning

confidence: 83%

Coating formulation change is the root cause for inferior bioefficacy of long-lasting insecticidal nets in Papua New Guinea

Anetul

et al. 2022

Preprint

Self Cite

In a study published in Nature Communications in August 2020, we demonstrated an abrupt decrease in the bioefficacy of long-lasting insecticidal nets (LLINs) for malaria prevention delivered to Papua New Guinea (PNG) between 2012 and 2013. This coincided with a rise in malaria cases in the country. At the time of publication of the original article, we were unable to pinpoint the exact reasons for the observed shift towards inferior product performance and stated that "further studies are required to determine the underlying cause of the observed reduced bioefficacy of these LLINs" 1. Due to the potentially significant public health implications (hundreds of millions of this specific LLIN product had been distributed globally), our study led to discussions and speculation among stakeholders. Here, we present data unequivocally showing that the observed reduction in the ability to kill mosquitoes of these LLINs is a direct result of a manufacturing change that occurred at the same time.

“…Unused PermaNet ® 2.0 nets manufactured in 2012 were obtained from the Madang Provincial Health Authority. Two groups of PermaNet ® 2.0 samples were included as they exhibit substantially different bioefficacy as shown in previous studies [ 12 , 26 ]. More details about the individual LLIN samples are provided in Additional File 1 .…”

Section: Methodsmentioning

confidence: 99%

WHO cone bioassay boards with or without holes: relevance for bioassay outcomes in long-lasting insecticidal net studies

Amos

et al. 2022

Malar J

Background The World Health Organization (WHO) cone bioassay is a key method used to evaluate the bioefficacy of long-lasting insecticidal nets (LLINs) used for malaria control. These tests also play an important role in LLIN product prequalification and longitudinal monitoring. Standardization of these assays is therefore important. While many parameters for WHO cone bioassays are defined in the respective WHO guidelines, others are not. One of these undefined parameters is the exact configuration of the bioassay boards. In cone bioassays, LLIN samples are pinned onto a bioassay board for testing. Anecdotal evidence suggests that bioassay boards with holes behind the LLIN samples lead to greater exposure to insecticide, as the mosquitoes are ‘forced to stand on the net material’. This may increase the key assay outcomes of 60 min knockdown (KD60) and 24 h mortality (M24). The present study tested this hypothesis in two facilities using two fully susceptible mosquito colonies. Methods WHO cone bioassays were performed using bioassay boards with holes and boards without holes in parallel, following WHO guidelines. Five brands of LLINs with four new and unwashed whole net samples per brand were used (total of n = 20 whole nets). Five pieces per whole net sample were prepared in duplicate resulting in a total of n = 100 pairs. Knock-down (KD) was recorded in 10 min intervals within the first hour after exposure and mortality was recorded at 24 h. Assays with Anopheles farauti were done at the Papua New Guinea Institute of Medical Research (PNGIMR) and assays with Aedes aegypti were done at James Cook University, Australia. Results Results varied not only with bioassay board configuration but also with mosquito colony. In particular, with An. farauti, a significantly higher M24 was observed when boards with holes were used, while this was not observed with Ae. aegypti. WHO cone bioassay results were systematically biased between the two facilities such that the use of An. farauti at PNGIMR predicted higher KD60 and M24. Conclusion The present study highlights the need for further harmonization of WHO cone bioassay methodology. Parameters such as bioassay board configuration and mosquito species systematically affect the observations, which impedes generalizability of WHO cone bioassay outcomes.