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

Koinari, Melanie, Bubun, Nakei, Amos, Brogan, Kiari, Kiari, Lahu, David, and Karl, Stephan (2022) WHO cone bioassay boards with or without holes: relevance for bioassay outcomes in long-lasting insecticidal net studies. Malaria Journal, 21. 389.

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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.

Item ID: 77558
Item Type: Article (Research - C1)
ISSN: 1475-2875
Keywords: Aedes, Anopheles, Bioassay board, Cone bioassay, Holes, LLIN, Long-lasting insecticidal nets, Mosquito, Pyrethroid
Copyright Information: © The Author(s) 2022. Open Access. This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data.
Funders: National Health and Medical Research Council (NHMRC)
Projects and Grants: NHMRC GNT2004390
Date Deposited: 07 Mar 2023 07:20
FoR Codes: 42 HEALTH SCIENCES > 4202 Epidemiology > 420207 Major global burdens of disease @ 100%
SEO Codes: 20 HEALTH > 2004 Public health (excl. specific population health) > 200404 Disease distribution and transmission (incl. surveillance and response) @ 100%
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