Browsing by Author "Mbuba, Emmanuel"

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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.
Estimating the hole surface area of insecticide-treated nets using image analysis, manual hole counting and exact hole measurements
(BMC, 2025-03-14) Mbuba, Emmanuel; Mañas‑Chavernas, Natalia; Moore, Sarah; Ruzige, Philipo; Kobe, Dickson; Moore, Jason; Philipo, Rose; Kisoka, Noela; Pontiggia, Gianpaolo; Chacky, Frank; Mwalimu, Charles; Cattin, Philippe; Wolleb, Julia; Sandkuehler, Robin; Ross, Amanda
Background The physical integrity of insecticidal‑treated nets (ITNs) is important for creating a barrier against host seeking mosquitoes and, therefore, influences people’s perception of the net’s effectiveness and their willingness to use it. Monitoring the physical integrity of ITNs over time provides information for replenishment schedules and purchasing decisions. Currently, the assessment of physical integrity of ITNs is conducted by manually counting holes and estimating their size to class the net as functional or not. This approach is laborious to routinely conduct during field surveys of ITNs. Automated image analysis may provide a rapid assessment of the physical integrity of ITNs but it is not known if the images can capture sufficient information. As a first step, this study aimed to assess the agreement between estimated hole surface areas derived from (1) manually segmented images, (2) manual hole counting compared to (3) ground truth obtained by calibrated close‑up shots of individual holes. Methods The physical integrity of 75 ITNs purposely selected from an ongoing study was assessed by manual hole counting, image analysis and ground truth. For the image analysis, a graphical user interface was developed and used for the segmentation of holes visible in photographs taken from each side of the net. The hole surface area was then computed from this data. The agreement between the estimates from image analysis and manual hole counting was compared to the ground truth using the Bland–Altman method. Results There was substantial agreement between the manually segmented image analysis estimates and the ground truth hole surface areas. The overall bias was small, with a mean ratio of the hole surface area from image analysis to the ground truth of 0.70, and the 95% limits of agreement ranging from 0.35 to 1.38. Manual hole counting underestimated the hole surface area compared to the ground truth, particularly among nets with holes above 10 cm in diameter. Conclusion Images coupled with manual segmentation contain sufficient information to calculate hole surface area. This lays the groundwork for incorporating automatic hole detection, and then assessing whether this method will offer a fast and objective method for routine assessment of physical integrity of ITNs. While the WHO
In starvation, a bone can also be meat”: a mixed methods evaluation of factors associated with discarding of long-lasting insecticidal nets in Bagamoyo, Tanzania
(Springer Nature., 2022-03-24) Madumla, Edith; Moore, Sarah; Moore, Jason; Mbuba, Emmanuel; Mbeyela, Edgar; Kibondo, Ummi; Mmbaga, Selemani; Kobe, Dickson; Baraka, Jitihada; Msellemu, Daniel; Swai, Johnson; Mboma, Zawadi; Odufuwa, Olukayode
Background: Between 2000 and 2019, more than 1.8 billion long-lasting insecticidal nets (LLINs) were distributed in Africa. While the insecticidal durability of LLINs is around 3 years, nets are commonly discarded 2 years post distribu tion. This study investigated the factors associated with the decision of users to discard LLINs. Methods: A mixed-method sequential explanatory approach using a structured questionnaire followed by focus group discussions (FGDs) to collect information on experiences, views, reasons, how and when LLINs are discarded. Out of 6,526 households that responded to the questionnaire of LLINs durability trial, 160 households were randomly selected from the households in four villages in Bagamoyo Tanzania for FGDs but only 155 households participated in the FGDs. Five of the household representatives couldn’t participate due to unexpected circumstances. A total of sixteen FGDs each comprising of 8–10 adults were conducted; older women (40–60 years), older men (40–60 years), younger women (18–39 years), younger men (18–39 years). During the FGDs, participants visually inspected seven samples of LLINs that were “too-torn” based on Proportionate Hole Index recommended by the World Health Organi zation (WHO) guidelines on LLIN testing, the nets were brought to the discussion and participants had to determine if such LLINs were to be kept or discarded. The study assessed responses from the same participants that attended FGD and also responded to the structured questionnaire, 117 participants fulflled the criteria, thus data from only 117 participants are analysed in this study. Results: In FGDs, integrity of LLIN infuenced the decision to discard or keep a net. Those of older age, women, and householders with lower income were more likely to classify a WHO “too-torn” net as “good”. The common methods used to discard LLINs were burning and burying. The fndings were seen in the quantitative analysis. For every addi tional hole, the odds of discarding a WHO “too-torn” LLIN increased [OR=1.05 (95%CI (1.04–1.07)), p<0.001]. Younger age group [OR=4.97 (95%CI (3.25–7.32)), p<0.001], male-headed households [OR=6.85 (95%CI (4.44 –10.59)), p<0.001], and wealthy households [OR=3.88 (95%CI (2.33–6.46)), p<0.001] were more likely to discard LLINs.
Laboratory efficacy of Bactivec ® and Griselesf ® biolarvicides used for large-scale larviciding in Tanzania
(Frontiers, 2025-07-21) Tegemeo, Gavana; Kailembo, Denis; Machange, Jane; Venance Michael; Swai, Kyeba; Olukayode, Odufuwa; Tenywa, Frank; Mwalimu, Charles; Jubilate Bernard; Samwel Lazaro; Best Yoram; Kajange, Stella; Kasagama, Elizabeth; Kisoka, Noela; Mbuba, Emmanuel; Chaki, Prosper; Lengeler, Christian; Moore, Sarah
From 2022 to 2024, a project piloting large-scale larviciding in Tanzania was implemented in Tanga Region. The project used in-country manufactured biolarvicides, The study was conducted at Ifakara Health Institute (IHI) in Tanzania. Laboratory-based dose–response experiments were performed using Bactivec® and Griselesf® against laboratory-reared early third instar larvae of Anopheles gambiae sensu stricto, Anopheles arabiensis, Anopheles funestus, Aedes aegypti and Culex quinquefasciatus. Larvae were exposed to various concentrations of Bactivec® and Griselesf®. VectoBac® served as a positive control, and distilled water as a negative control. Twelve replicates per concentration, with 25 larvae per replicate, were tested. Larval mortality was recorded at 24 and 48 hours after exposure to Bactivec® and Griselesf®, respectively. Probit regression analysis was used to determine the lethal concentration (LC50 and LC90) values.Bactivec® and Griselesf®. This study independently assessed the efficacy of both biolarvicide products to ensure that they represented a good option for scaling up.
Long-lasting insecticidal nets retain bio-efficacy after 5 years of storage: implications for malaria control programmes
(Springer Nature, 2020-03-14) Musa, Jeremiah John; Moore, Sarah; Moore, Jason; Mbuba, Emmanuel; Mbeyela, Edgar; Kobe, Dickson; Swai, Johnson; Odufuwa, Olukayode
Background: Long-lasting insecticidal nets (LLINs) are the most sustainable and efective malaria control tool currently available. Global targets are for 80% of the population living in malaria endemic areas to have access to (own) and use a LLIN. However, current access to LLINs in endemic areas is 56% due to system inefciencies and budget limitations. Thus, cost-efective approaches to maximize access to efective LLINs in endemic areas are required. This study evaluated whether LLINs that had been stored for 5 years under manufacturer’s recommended conditions may be optimally efective against Anopheles mosquitoes, to inform malaria control programmes and governments on the periods over which LLINs may be stored between distributions, in an efort to maximize use of available LLINs. Methods: Standard World Health Organization (WHO) bioassays (cone and tunnel test) were used to evaluate the bio-efcacy and wash resistance of Olyset® and DawaPlus® 2.0 (rebranded Tsara® Soft) LLINs after 5 years of storage at 25 °C to 33.4 °C and 40% to 100% relative humidity. In addition, a small scale Ifakara Ambient Chamber test (I-ACT) was conducted to compare the bio-efcacy of one long stored LLINs to one new LLIN of the same brand, washed or unwashed. LLINs were evaluated using laboratory reared fully susceptible Anopheles gambiae sensu stricto (s.s.) (Ifakara strain) and pyrethroid resistant Anopheles arabiensis (Kingani strain). Results: After 5 years of storage, both unwashed and washed, Olyset® and DawaPlus® 2.0 (Tsara® Soft) LLINs passed WHO bio-efcacy criteria on knockdown (KD60) ≥95%, 24-h mortality ≥80% and ≥90% blood-feeding inhibition in WHO assays against susceptible An. gambiae s.s. DawaPlus® 2.0 LLINs also passed combined WHO bioassay criteria against resistant An. arabiensis. Confrmatory I-ACT tests using whole nets demonstrated that long-stored LLINs showed higher efcacy than new LLINs on both feeding inhibition and mortality endpoints against resistant strains. Conclusions: Even after long-term storage of around 5 years, both Olyset® and DawaPlus® 2.0 LLINs remain efcacious against susceptible Anopheles mosquitoes at optimal storage range of 25 °C to 33.4 °C for temperature and 40% to 100% relative humidity measured by standard WHO methods. DawaPlus® 2.0 (Tsara® Soft) remained efcacious against resistant strain.
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.
SC Johnson Guardian™ spatial repellent shows 1-year efficacy against wild pyrethroid-resistant Anopheles arabiensis, with a similar blood-feeding inhibition efficacy to Mosquito Shield™ in a Tanzanian experimental hut trial
(Frontiers, 2025-06-23) Swai, Johnson; Ntabaliba, Watson; Mbuba, Emmanuel; Ngoyani, Hassan; Makungwa, Noely; Mseka, Antony; Bradley, John; Chura, Madeleine; Mascari, Thomas; Moore, Sarah Jane
Background: Spatial repellents (SRs) that passively emanate airborne concentrations of an active ingredient within a space disrupt mosquito behaviors to reduce human-vector contact. A clinical trial of SC Johnson’s Mosquito Shield™ (Mosquito Shield) demonstrated a 33% protective efficacy against malaria in Kenya. Mosquito Shield lasts for 1 month, but a longer duration product is needed for malaria control programs. SC Johnson’s Guardian™ (Guardian) is designed to provide longer continuous protection from disease-transmitting mosquitoes. Methods: We conducted experimental hut trials to i) evaluate the efficacy of Guardian over 12 months (between May 2022 and May 2023) and ii) assess the potential public health utility of Guardian by comparing it to Mosquito Shield over 1 month (midway through the Guardian evaluation in November 2022) against wild pyrethroid-resistant malaria vector mosquitoes. The primary endpoint was the number of blood-fed Anopheles arabiensis, while secondary endpoints were the proportion of dead An. arabiensis at 24 hours and the proportion of blood-fed mosquitoes. For Guardian, the number of mosquito landings was also evaluated by human landing catch, a method routinely used in community or implementation studies. Results: Over 12 months of continuous use, Guardian reduced the number of An. arabiensis blood-feeding by 82.7% [95% confidence interval (78.5%–86.1%)] and landing by 65.1% (59.4%– 70.0%). Guardian also induced 20.1% mortality (18.4%–21.8%). Guardian was found to be superior to Mosquito Shield in reducing the number of blood-fed An. arabiensis with similar proportions of blood-fed and dead mosquitoes at 24 hours. Conclusion: Guardian was effective in reducing blood-feeding and landing of wild pyrethroid-resistant malaria vectors for 12 months and shows superior protective efficacy compared to Mosquito Shield in reducing the overall number of blood-feeding mosquitoes. Experimental hut studies are suitable for comparative evaluations of new spatial repellent products because they precisely estimate entomological endpoints elicited by spatial repellents known to significantly impact vectorial capacity and disease transmission.