Cone Bioassays Provide Reproducible Bioefficacy Estimates with Different Anopheline Mosquitoes and Can Be Used for Quality Assurance of Pyrethroid Insecticide Treated Nets
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Date
2022-01-24
Journal Title
Journal ISSN
Volume Title
Publisher
Research Square
Abstract
Background
Quality assurance (QA) of insecticide-treated nets (ITNs) delivered to malaria-endemic countries is conducted by measuring physiochemical
parameters, but not bioecacy against malaria mosquitoes. The cone bioassay provides a simple evaluation of ITN bioecacy and its
conditions and parameters are prescribed by the World Health Organization (WHO). This study explored utility of cone bioassays for pre-
delivery QA of pyrethroid ITNs in two test facilities using different mosquito species to test the assumption that cone bioassays are consistent
and reproducible across locations, mosquito strains, and laboratories.
Methods
Double-blinded bioassays were conducted on unused pyrethroid ITNs of 4 brands (5 nets/brand, 5 subsamples/net) that had been delivered for
mass distribution in Papua New Guinea (PNG) having passed physiochemical testing of chemical content. Cone bioassays were performed on
adjacent net pieces following WHO guidelines at the PNG Institute of Medical Research (PNGIMR) using pyrethroid susceptible
Anopheles
farauti s.s. and at Ifakara Health Institute (IHI), Tanzania using pyrethroid susceptible
Anopheles gambiae s.s. Additionally, WHO tunnel tests
was conducted at IHI on ITNs that did not meet cone bioecacy thresholds. Results from IHI and PNGIMR were compared using Spearman’s
Rank, Bland Altman and Cohen’s kappa. A literature review on the utility of cone bioassays for unused pyrethroid ITNs testing was also
conducted.
Results
In cone bioassays, 13/20 nets (65%) met WHO bioecacy criteria at IHI and 8/20 (40%) at PNGIMR. All nets met WHO bioecacy criteria on
combined cone/tunnel tests. Results from IHI and PNGIMR correlated on 60-minute knockdown (rs=0.6,
p=0.002,n=20) and 24-hour mortality
(rs=0.9,
p<0.0001,n=20) but there was systematic bias between the results measured by Bland Altman. Of the 5 nets with discrepant result
between IHI and PNGIMR, three had condence intervals overlapping the 80% mortality threshold, with averages within 1-3% of the threshold.
The agreement between the results to predict ITN failure was good with kappa=0.79 (0.53-1.00) and 90% accuracy.
Conclusions
WHO cone is a reproducible means to measure pyrethroid ITN bioecacy using a combination of knockdown and mortality. In the absence of
an alternative tests, cone tests could be used to assess the availability of active ingredients at the surface of ITN (where mosquitoes encounter
it) as part of pre-delivery QA.
Sustainable Development Goals
This research article was published in the Research Square, 2022
Keywords
Infectious Diseases, Bioefficacy, Bioassay, Cone bioassay, Tunnel test, Insecticide treated nets, Long lasting insecticidal nets, Pyrethroid, Mosquito, Anopheles, Malaria