Browsing by Author "Kamande, Dismas"

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Comparison of cone bioassay estimates at two laboratories with different Anopheles mosquitoes for quality assurance of pyrethroid insecticide-treated nets
(Springer Nature., 2022-07-07) Mbwambo, Stephen; Bubun, Nakei; Mbuba, Emmanuel; Moore, Jason; Mbina, Kasiani; Kamande, Dismas; Laman, Moses; Mpolya, Emmanuel; Odufuwa, Olukayode; Freeman, Tim; Karl, Stephan; Moore, Sarah
ckground: Quality assurance (QA) of insecticide-treated nets (ITNs) delivered to malaria-endemic countries is con ducted by measuring physiochemical parameters, but not bioefcacy against malaria mosquitoes. This study explored utility of cone bioassays for pre-delivery QA of pyrethroid ITNs to test the assumption that cone bioassays are consist ent across locations, mosquito strains, and laboratories. Methods: Double-blinded bioassays were conducted on twenty unused pyrethroid ITNs of 4 brands (100 nets, 5 subsamples per net) that had been delivered for mass distribution in Papua New Guinea (PNG) having passed pre delivery inspections. Cone bioassays were performed on the same net pieces following World Health Organization (WHO) guidelines at the PNG Institute of Medical Research (PNGIMR) using pyrethroid susceptible Anopheles farauti sensu stricto (s.s.) and at Ifakara Health Institute (IHI), Tanzania using pyrethroid susceptible Anopheles gambiae s.s. Additionally, WHO tunnel tests were conducted at IHI on ITNs that did not meet cone bioefcacy thresholds. Results from IHI and PNGIMR were compared using Spearman’s Rank correlation, Bland–Altman (BA) analysis and analysis of agreement. Literature review on the use of cone bioassays for unused pyrethroid ITNs testing was conducted. Results: In cone bioassays, 13/20 nets (65%) at IHI and 8/20 (40%) at PNGIMR met WHO bioefcacy criteria. All nets met WHO bioefcacy criteria on combined cone/tunnel tests at IHI. Results from IHI and PNGIMR correlated on 60-min knockdown (KD60) (rs=0.6,p=0.002,n=20) and 24-h mortality (M24) (rs=0.9,p<0.0001,n=20) but BA showed systematic bias between the results. Of the 5 nets with discrepant result between IHI and PNGIMR, three had confdence intervals overlapping the 80% mortality threshold, with averages within 1–3% of the threshold. Including these as a pass, the agreement between the results to predict ITN failure was good with kappa=0.79 (0.53–1.00) and 90% accuracy. Conclusions: Based on these study fndings, the WHO cone bioassay is a reproducible bioassay for ITNs with>80% M24, and for all ITNs provided inherent stochastic variation and systematic bias are accounted for. The literature
Cone Bioassays Provide Reproducible Bioefficacy Estimates with Different Anopheline Mosquitoes and Can Be Used for Quality Assurance of Pyrethroid Insecticide Treated Nets
(Research Square, 2022-01-24) Mbwambo, Stephen; Bubun, Nakei; Mbuba, Emmanuel; Moore, Jason; Mbina, Kasiani; Kamande, Dismas; Laman, Moses; Mpolya, Emmanuel; Odufuwa, Olukayode; Freeman, Tim; Karl, Stephan; Moore, Sarah
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.
Modified who tunnel test for high through put evaluation of insecticide-treated nets considering the effects of hosts, exposure time and mosquito density
(NM-AIST, 2022-08) Kamande, Dismas
The standard World Health Organization (WHO) tunnel test is a reliable laboratory bioassay used for "free flying" testing of Insecticide Treated Net (ITN) bio-efficacy. Multiple parameters affect the outcomes measured in tunnel tests. Therefore, a comparison of hosts, exposure time, and mosquito density against the current gold standard test (100 mosquitoes, animal bait and 12-hours exposure) was conducted following ITNs evaluation guidelines. A series of experiments were conducted in the WHO tunnel bioassay to evaluate the bio-efficacy endpoints, mortality at 24- hours (M24) and 72-hours (M72), blood feeding success (BFS), and blood feeding inhibition (BFI). The following parameters were evaluated: 1) baits (rabbit, membrane, human arm), 2) exposure time in the tunnel (1-hours vs 12-hours), and 3) mosquito density (50 vs 100 mosquitoes per test). Finally, an alternative bioassay using a membrane with 50 mosquitoes was compared to the gold standard bioassay. Resistant Anopheles arabiensis and susceptible Anopheles gambiae were used to evaluate Interceptor® and Interceptor®G2 ITNs. Similar trends in mortality and BFI were observed for both ITNs using the gold standard WHO tunnel test or alternative bioassays. Mortality and BFS were not statistically different when rabbits were the bait or when 50 or 100 mosquitoes of either strains used. No systematic difference was observed for the agreement by Bland and Altman's methods (B&A) with a mean difference 4.54% in blood feeding and 1.71% for M72. When comparing membrane with 50 mosquitoes and rabbit with 100 mosquito, no systematic difference was observed for the agreement with mean difference 9.06% for blood feeding and -5.44% for M72. These results demonstrate that WHO tunnel tests using rabbit bait run with 50 mosquitos’ measures similar outcome compared to gold standard bioassay. In addition, using a membrane feeder with 50 mosquitoes is a potential replacement for the WHO tunnel bioassay with animal bait and merits further studies at other laboratories to corroborate these findings.
Modified World Health Organization (WHO) Tunnel Test for Higher Throughput Evaluation of Insecticide-Treated Nets (ITNs) Considering the Effect of Alternative Hosts, Exposure Time, and Mosquito Density
(MDPI, 2022-06-21) Kamande, Dismas; Odufuwa, Olukayode; Mbuba, Emmanuel; Hofer, Lorenz; Moore, Sarah
The standard World Health Organization (WHO) tunnel test is a reliable laboratory bioassay used for “free-flying” testing of insecticide-treated nets (ITNs) bio-efficacy where mosquitoes pass through a ITN sample to reach a live animal bait. Multiple parameters (i.e., bait, exposure time, and mosquito density) may affect the outcomes measured in tunnel tests. Therefore, a comparison was conducted of alternative hosts, exposure time, and lower mosquito density against the current gold standard test (100 mosquitoes, animal bait, and 12-h exposure) as outlined in the WHO ITN evaluation guideline. This was done with the aim to make the tunnel test cheaper and with higher throughput to meet the large sample sizes needed for bio-efficacy durability monitoring of chlorfenapyr ITNs that must be evaluated in “free-flying” bioassays. Methods: A series of experiments were conducted in the WHO tunnel test to evaluate the impact of the following factors on bio-efficacy endpoints of mosquito mortality at 24-h (M24) and 72-h (M72) and blood-feeding success (BFS): (1) baits (rabbit, membrane, human arm); (2) exposure time in the tunnel (1 h vs. 12 h); and (3) mosquito density (50 vs. 100). Finally, an alternative bioassay using a membrane with 50 mosquitoes (membrane-50) was compared to the gold standard bioassay (rabbit with 100 mosquitoes, rabbit-100). Pyrethroid-resistant Anopheles arabiensis and pyrethroid susceptible Anopheles gambiae were used to evaluate Interceptor® and Interceptor® G2 ITNs. Results: Using a human arm as bait gave a very different BFS, which impacted measurements of M24 and M72. The same trends in M24, M72 and BFS were observed for both Interceptor® ITN and Interceptor® G2 unwashed and washed 20 times measured using the gold standard WHO tunnel test (rabbit-100) or rabbit with 50 mosquitoes (rabbit-50). M24, M72 and BFS were not statistically different when either 50 or 100 mosquitoes were used with rabbit bait in the tunnel bioassay for either the susceptible or resistant strains. No systematic difference was observed between rabbit-50 and rabbit-100 in the agreement by the Bland and Altman method (B&A). The mean difference was 4.54% (−22.54–31.62) in BFS and 1.71% (−28.71–32.12) in M72 for rabbit-50 versus rabbit-100. Similar M24, M72 and lower BFS was measured by membrane-50 compared to rabbit-100. No systematic difference was observed in the agreement between membrane-50 and rabbit-100, by B&A. The mean difference was 9.06% (−11.42–29.64) for BSF and −5.44% (−50.3–39.45) for M72. Both membrane-50, rabbit-50 and rabbit-100 predicted the superiority of Interceptor® G2 over Interceptor® ITN for the resistant strain on M72. Conclusion: These results demonstrate that WHO tunnel tests using rabbit bait may be run with 50 mosquitoes to increase sample sizes needed for bio-efficacy durability monitoring of ITNs in “free-flying” bioassays. Using a membrane feeder with 50 mosquitoes is a potential replacement for the WHO tunnel bioassay with animal bait if control blood feeding rates can be improved to 50% because blood feeding impacts mosquito survival after exposure to insecticides.