BackgroundAn increasing number of countries in sub-Saharan Africa are moving towards malaria-elimination, mostly thanks to successful vector control campaigns. However, elimination has proven challenging, resulting in the persistence of malaria transmission. It is now accepted that in order to eliminate malaria, new complementary vector control approaches must be developed. This study describes the development of a sugar-baited resting place containing a toxic dose of ivermectin for the control of Anopheles arabiensis.ResultsDose response experiments were performed in insectary conditions to determine the LD90 of ivermectin against An. arabiensis. Over 95% of An. arabiensis were knocked down 48 h post-sugar feeding on 10% sucrose solutions containing 0.01% ivermectin. When investigating different juices as attractants, it was observed that An. arabiensis preferred orange, watermelon and commercial guava juice over pawpaw, tomato, mango or banana, but were most likely to feed on simple 10% sugar solution. Using recycled materials, different bait prototypes were tested to determine the best design to maximize sugar feeding. Baits that offered a resting place for the mosquito rather than just a surface to sugar feed were more likely to attract An. arabiensis to sugar feed. The optimized prototype was then placed in different locations within a screen-house, colour-coded with different food dyes, containing competing vegetation (Ricinus communis) and experimental huts where humans slept under bed nets. Around half of all the released An. arabiensis sugar fed on the sugar baits, and approximately 50% of all sugar fed mosquitoes chose the baits close to outdoor vegetation before entering the huts.ConclusionsIvermectin is an effective insecticide for use in sugar baits. The design of the sugar bait can influence feeding rates and, therefore, efficacy. Sugar baits that offer a resting surface are more efficient and sugar feeding on the baits is maximized when these are placed close to peri-domestic vegetation. Attractive toxic sugar baited resting places may provide an additional vector control method to complement with existing strategies.

BackgroundMalaria elimination is unlikely to be achieved without the implementation of new vector control interventions capable of complementing insecticide-treated nets and indoor residual spraying. Attractive-toxic sugar baits (ATSBs) are considered a new vector control paradigm. They are technologically appropriate as they are simple and affordable to produce. ATSBs kill both female and male mosquitoes attracted to sugar feed on a sugary solution containing a mosquitocidal agent and may be used indoors or outdoors. This study explored the views and perceptions on ATSBs of community members from three Coastal Tanzanian communities.MethodsThree communities were chosen to represent coastal urban, peri-urban and rural areas. Sensitization meetings were held with a total of sixty community members where ATSBs were presented and explained their mode of action. At the end of the meeting, one ATSB was given to each participant for a period of 2 weeks, after which they were invited to participate in focus group discussions (FGDs) to provide feedback on their experience.ResultsOver 50% of the participants preferred to use the bait indoors although they had been instructed to place it outdoors. Participants who used the ATSBs indoors reported fewer mosquitoes inside their homes, but were disappointed not to find the dead mosquitoes in the baits, although they had been informed that this was unlikely to happen. Most participants disliked the appearance of the bait and some thought it to be reminiscent of witchcraft. Neighbours that did not participate in the FGDs or sensitizations were sceptical of the baits.ConclusionsThis study delivers insight on how communities in Coastal Tanzania are likely to perceive ATSBs and provides important information for future trials investigating the efficacy of ATSBs against malaria. This new vector control tool will require sensitization at community level regarding its mode of action in order to increase the acceptance and confidence in ATSBs for mosquito control given that most people are not familiar with the new paradigm. A few recommendations for product development and delivery are discussed.

Background Vector mosquito biting intensity is an important measure to understand malaria transmission. Human landing catch (HLC) is an effective but labour-intensive, expensive, and potentially hazardous entomological surveillance tool. The Centres for Disease Control light trap (CDC-LT) and the human decoy trap (HDT) are exposure-free alternatives. This study compared the CDC-LT and HDT against HLC for measuring Anopheles biting in rural Tanzania and assessed their suitability as HLC proxies. Methods Indoor mosquito surveys using HLC and CDC-LT and outdoor surveys using HLC and HDT were conducted in 2017 and in 2019 in Ulanga, Tanzania in 19 villages, with one trap/house/night. Species composition, sporozoite rates and density/trap/night were compared. Aggregating the data by village and month, the Bland–Altman approach was used to assess agreement between trap types. Results Overall, 66,807 Anopheles funestus and 14,606 Anopheles arabiensis adult females were caught with 6,013 CDC-LT, 339 indoor-HLC, 136 HDT and 195 outdoor-HLC collections. Indoors, CDC-LT caught fewer An. arabiensis (Adjusted rate ratio [Adj.RR] = 0.35, 95% confidence interval [CI]: 0.27–0.46, p < 0.001) and An. funestus (Adj.RR = 0.63, 95%CI: 0.51–0.79, p < 0.001) than HLC per trap/night. Outdoors, HDT caught fewer An. arabiensis (Adj.RR = 0.04, 95%CI: 0.01–0.14, p < 0.001) and An. funestus (Adj.RR = 0.10, 95%CI: 0.07–0.15, p < 0.001) than HLC. The bias and variability in number of mosquitoes caught by the different traps were dependent on mosquito densities. The relative efficacies of both CDC-LT and HDT in comparison to HLC declined with increased mosquito abundance. The variability in the ratios was substantial for low HLC counts and decreased as mosquito abundance increased. The numbers of sporozoite positive mosquitoes were low for all traps. Conclusions CDC-LT can be suitable for comparing mosquito populations between study arms or over time if accuracy in the absolute biting rate, compared to HLC, is not required. CDC-LT is useful for estimating sporozoite rates because large numbers of traps can be deployed to collect adequate mosquito samples. The present design of the HDT is not amenable for use in large-scale entomological surveys. Use of HLC remains important for estimating human exposure to mosquitoes as part of estimating the entomological inoculation rate (EIR).

Background N,N-Diethyl-3-methylbenzamide (DEET) topical mosquito repellents are effective personal protection tools. However, DEET-based repellents tend to have low consumer acceptability because they are cosmetically unappealing. More attractive formulations are needed to encourage regular user compliance. This study evaluated the protective efficacy and protection duration of a new topical repellent ointment containing 15% DEET, MAÏA® compared to 20% DEET in ethanol using malaria and dengue mosquito vectors in Bagamoyo Tanzania. Methods Fully balanced 3 × 3 Latin square design studies were conducted in large semi-field chambers using laboratory strains of Anopheles gambiae sensu stricto, Anopheles arabiensis and Aedes aegypti. Human volunteers applied either MAÏA® ointment, 20% DEET or ethanol to their lower limbs 6 h before the start of tests. Approximately 100 mosquitoes per strain per replicate were released inside each chamber, with 25 mosquitoes released at regular intervals during the collection period to maintain adequate biting pressure throughout the test. Volunteers recaptured mosquitoes landing on their lower limbs for 6 h over a period of 6 to 12-h post-application of repellents. Data analysis was conducted using mixed-effects logistic regression. Results The protective efficacy of MAÏA® and 20% DEET was not statistically different for each of the mosquito strains: 95.9% vs. 97.4% against An. gambiae (OR = 1.53 [95% CI 0.93–2.51] p = 0.091); 96.8% vs 97.2% against An. arabiensis (OR = 1.08 [95% CI 0.66–1.77] p = 0.757); 93.1% vs 94.6% against Ae. aegypti (OR = 0.76 [95% CI 0.20–2.80] p = 0.675). Average complete protection time (CPT) in minutes of MAÏA® and that of DEET was similar for each of the mosquito strains: 571.6 min (95% CI 558.3–584.8) vs 575.0 min (95% CI 562.1–587.9) against An. gambiae; 585.6 min (95% CI 571.4–599.8) vs 580.9 min (95% CI 571.1–590.7) against An. arabiensis; 444.1 min (95% CI 401.8–486.5) vs 436.9 min (95% CI 405.2–468.5) against Ae. aegypti. Conclusions MAÏA® repellent ointment provides complete protection for 9 h against both An. gambiae and An. arabiensis, and 7 h against Ae. aegypti similar to 20% DEET (in ethanol). MAÏA® repellent ointment can be recommended as a tool for prevention against outdoor biting mosquitoes in tropical locations where the majority of the people spend an ample time outdoor before going to bed.

Background The control of vector borne arboviral diseases such as Dengue is mainly achieved by reducing human-vector contact and controlling the vectors through source reduction and environmental management. These measures are constrained by labour intensity, insecticide resistance and pro-active community participation. The current study intended to develop and test an ivermectin-based attractive-targeted sugar bait (ATSB) against Aedes aegypti. Methods The 48hour lethal concentration (LC90) of ivermectin against Ae. aegypti was determined through serial dilution experiment where five 30cm x 30cm x 30cm cages were set; into each, a 10% sugar solution treated with ivermectin were introduced. 40 Ae. aegypti were released into each cage and observed for mortality after 4, 8, 24 and 48 hours. The ivermectin-based ATSB was evaluated in a semi field system where ATSB and attractive sugar bait (ASB) were deployed into each compartment of the semi field and 100 female Ae. aegypti were released every day and recaptured the next day through human land catch and Bio-gent sentinel trap. The developed and semi-field tested ATSB was further tested in the field by deploying them in garages. Results The ivermectin 48hr LC90 of male and female Ae. aegypti was found to be 0.03% w/v. In the semi field system, the ATSB significantly reduced a free-flying population of Ae. aegypti within 24 hours (incidence rate ratio (IRR) = 0.62; [95% confidence interval (95%CI); 0.54-0.70] and p-value < 0.001). However, in the field, the ATSBs required the addition of yeast as a carbon dioxide source to efficiently attract Ae. aegypti mosquitoes to feed. Conclusion Ivermectin is an active ingredient that can be used in an ATSB for Ae. aegypti depopulation. However, further research is needed to improve the developed and tested ATSB to compete with natural sources of sugar in a natural environment.

Background: N,N-Diethyl-3-methylbenzamide (DEET) topical mosquito repellents are effective personal protection tools. However, DEET repellents tend to have low consumer acceptability because they are cosmetically unappealing. More attractive formulations are needed to encourage regular compliance. This study evaluated the protective efficacy and duration of protection of a new topical repellent ointment, MAÏA® compared to 20% DEET in ethanol using malaria and dengue mosquito vectors in Tanzania.Methods: Fully balanced 3x3 Latin square design studies were conducted in large semi-field chambers using laboratory strains of Anopheles gambiae s.s, Anopheles arabiensis and Aedes aegypti. Human volunteers applied either MAÏA® ointment, 20% DEET or ethanol to their lower limbs six hours before the start of tests. Approximately 100 mosquitoes per strain per replicate were released inside each chamber, with 25 mosquitoes released at regular intervals during the collection period to maintain adequate biting pressure throughout the test. Volunteers recaptured mosquitoes landing on their lower limbs for six hours over a period of six to 12-hours post-application of repellents. Data analysis was conducted using mixed-effects logistic regression.Results: The protective efficacy of MAÏA® and 20% DEET was not different for each of the mosquito strains: 95.9% vs 97.4% against An. gambiae (OR=1.53 [95% CI: 0.93–2.51] p=0.091); 96.8% vs 97.2% against An. arabiensis (OR =1.08 [95% CI: 0.66 –1.77] P=0.757); 93.1% vs 94.6% against Ae. aegypti (OR=0.76 [95% CI: 0.20-2.80] p=0.675). Average complete protection time (CPT) of MAÏA® and that of DEET was similar for each of the mosquito strains: 571.6 minutes (95% CI: 558.3-584.8) vs 575.0 minutes (95% CI: 562.1-587.9) against An. gambiae; 585.6 minutes (95% CI: 571.4-599.8) vs 580.9 minutes (95% CI: 571.1-590.7) against An. arabiensis; 444.1 minutes (95% CI: 401.8-486.5) vs 436.9 minutes (95% CI: 405.2-468.5) against Ae. aegypti.Conclusions: MAÏA® repellent ointment provides complete protection for 9 hours against both An. gambiae and An. arabiensis, and 7 hours against Ae. aegypti similar to 20% DEET (in ethanol). MAÏA® repellent ointment can be recommended as a tool for prevention of outdoor biting mosquitoes in tropical locations with a suggested reapplication time of 6 hours.

Background N, N-Diethyl-3-methylbenzamide (DEET) topical mosquito repellents are effective personal protection tools. However, DEET-based repellents tend to have low consumer acceptability because they are cosmetically unappealing. More attractive formulations are needed to encourage regular user compliance. This study evaluated the protective efficacy and protection duration of a new topical repellent ointment containing 15% DEET, MAÏA® compared to 20% DEET in ethanol using malaria and dengue mosquito vectors in Bagamoyo Tanzania.Methods Fully balanced 3x3 Latin square design studies were conducted in large semi-field chambers using laboratory strains of Anopheles gambiae sensu stricto, Anopheles arabiensis and Aedes aegypti. Human volunteers applied either MAÏA® ointment, 20% DEET or ethanol to their lower limbs six hours before the start of tests. Approximately 100 mosquitoes per strain per replicate were released inside each chamber, with 25 mosquitoes released at regular intervals during the collection period to maintain adequate biting pressure throughout the test. Volunteers recaptured mosquitoes landing on their lower limbs for six hours over a period of six to 12-hours post-application of repellents. Data analysis was conducted using mixed-effects logistic regression.Results The protective efficacy of MAÏA® and 20% DEET was not different for each of the mosquito strains: 95.9% vs 97.4% against An. gambiae (OR=1.53 [95% CI: 0.93–2.51] p=0.091); 96.8% vs 97.2% against An. arabiensis (OR =1.08 [95% CI: 0.66 –1.77] P=0.757); 93.1% vs 94.6% against Ae. aegypti (OR=0.76 [95% CI: 0.20-2.80] p=0.675). Average complete protection time (CPT) of MAÏA® and that of DEET was similar for each of the mosquito strains: 571.6 minutes (95% CI: 558.3-584.8) vs 575.0 minutes (95% CI: 562.1-587.9) against An. gambiae; 585.6 minutes (95% CI: 571.4-599.8) vs 580.9 minutes (95% CI: 571.1-590.7) against An. arabiensis; 444.1 minutes (95% CI: 401.8-486.5) vs 436.9 minutes (95% CI: 405.2-468.5) against Ae. aegypti.Conclusions MAÏA® repellent ointment provides complete protection for 9 hours against both An. gambiae and An. arabiensis, and 7 hours against Ae. aegypti similar to 20% DEET (in ethanol). MAÏA® repellent ointment can be recommended to be used as a tool for prevention of outdoor biting mosquitoes in tropical locations as it protects for more than 6 hours.

Background Sugar feeding behaviour is an essential aspect for mosquito survival, fitness, reproduction, and competence. Understanding the behaviour of Aedes aegypti is a fundamental phenomenon for the development of new interventions for controlling the vectors. The objective of the current study was to investigate i) the time in an Ae. aegyptimosquito’s adult life when they are most likely to sugar feed ii) if sugar sources availability limits Ae. aegypti blood feeding with the aim of informing control strategies using attractive-targeted sugar baits (ATSBs) Methods: The preference of Ae. aegypti to feed on sugar or blood and the effect of sugar source availability on Ae. aegypti blood feeding was studied at different chronological and physiological ages in semi-field conditions in Bagamoyo, Tanzania. Experiments were done through a series of paired–choice assays whereupon mosquitoes were allowed to choose between a sugar meal or a blood meal in the form of a rabbit. Results In the first five days post emergence, Aedes aegypti mosquitoes were equally likely to opt for a sugar meal or a blood meal. However, after the first gonotrophic cycle Ae. aegypti prefer to feed on blood meal (OR=9.4; 95%CI= [6.7-13.0]; p<0.001) over a sugar meal (OR=1). Moreover, a nulliparous Ae. aegypti mosquitoes are less likely to blood feed if they have both sugar and blood sources available (OR=0.06; 95%CI [0.02-0.16] p<0.001). Conclusion In this study, sugar meal is observed to be a part of Ae. aegypti life particularly at the younger stage (nulliparous stage). Therefore, there is potential for the development of interventions such as attractive toxic sugar baits (ATSBs).