Background Long-lasting insecticidal nets (LLINs) are the most sustainable and effective 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 inefficiencies and budget limitations. Thus, cost-effective approaches to maximize access to effective 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 effective against Anopheles mosquitoes, to inform malaria control programmes and governments on the periods over which LLINs may be stored between distributions, in an effort to maximize use of available LLINs. Methods Standard World Health Organization (WHO) bioassays (cone and tunnel test) were used to evaluate the bio-efficacy 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-efficacy 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-efficacy 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. Confirmatory I-ACT tests using whole nets demonstrated that long-stored LLINs showed higher efficacy 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 efficacious 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 efficacious against resistant strain.

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.

Long Lasting Insecticidal Nets (LLINs) are the most sustainable and effective malaria control tool currently available. Global targets are for ≥80% of the population living in malaria endemic areas to have access to and use a LLIN. However, current access to LLINs in endemic areas is 56% due to system inefficiencies and budget limitations. Thus, cost-effective approaches to maximize access of effective LLINs in endemic areas are required. This study evaluated whether LLINs that had been stored for more than five years under manufacturer recommended conditions may be optimally effective against Anopheles mosquitoes, to inform malaria control programs and governments on the periods over which LLINs may be stored between distributions, in an effort to maximise use of available LLINs. Standard World Health Organization (WHO) bioassays (cone and tunnel tests) were used to evaluate the bio-efficacy and wash resistance of Olyset ® and DawaPlus ® 2.0 (rebranded Tsara ® Soft) LLINs after five years of storage at 25 C - 33.4C and 40%-100% relative humidity. In addition, a small scale Ifakara Ambient Chamber test (I-ACT) was conducted to compare bio-efficacy of one long stored LLIN to one new LLIN of the same brand, unwashed and washed. Long-lasting insecticidal nets were evaluated using laboratory reared fully susceptible Anopheles gambiae sensu stricto (s.s) (Ifakara str ain) and pyrethroid resistant Anopheles arabiensis (Kingani strain). After five years of storage, both unwashed and washed Olyset ® and DawaPlus ® 2.0 LLINs passed WHO efficacy criteria on Knockdown (KD60) ≥95%, 24-h r mortality ≥ 80% and ≥90% blood-feeding inhibition as per conducted WHO bioassays against susceptible An. gambiae s.s. The DawaPlus ® 2.0 LLINs also passed combined WHO bio-assay criteria against resistant An. arabiensis. Confirmatory I-ACT test using whole nets demonstrated that long stored LLINs showed similar efficacy to new LLINs on both feeding inhibition and mortality endpoints against susceptible and resistant strains. Therefore, even after long storage of around 5 years, both Olyset ® and DawaPlus ® 2.0 remain efficacious against susceptible Anopheles mosquitoes at optimal storage range of 25 C - 33.4C and 40%-100% relative humidity measured by standard WHO methods. DawaPlus ® 2.0 remained efficacious against pyrethroid-resistant strain.

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).