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Title: Exploitation of adult Anopheles arabiensis behaviour and ecology for the dissemination of pyriproxyfen : a novel technique for malaria vector control in Tanzania
Author: Lwetoijera, Dickson
ISNI:       0000 0004 6058 5637
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2016
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Effective larviciding to manage mosquito aquatic habitats offers an additional strategy for malaria vector control by complementing benefits already achieved by long lasting insecticidetreated nets (LLINs) and indoor residual spraying (IRS). Sustainable implementation of larviciding requires comprehensive understanding of the ecology of disease vectors and robust monitoring of factors governing local disease transmission. Treatment of aquatic habitats with the juvenile hormone analogue Pyriproxyfen (PPF), inhibits adult mosquito emergence at extremely low concentrations that are potentially deliverable by PPF-contaminated gravid adult females, a phenomenon termed „autodissemination‟. The primary aim of this thesis was to investigate a range of adult mosquito behaviours that might be exploited to disseminate PPF. The effectiveness of PPF to sterilize adult mosquitoes for malaria vector control was also assessed in a controlled system. Vector dynamics, malaria transmission intensity and risk factors were evaluated at the field site where the PPF autodissemination strategy would be evaluated in field trials and potentially implemented. Field monitoring of indoor malaria transmission risk factors revealed that even in the communities with high coverage of bednets, LLINs did not reduce the indoor densities of An. gambiae s.l (RR= 0.74 (0.50 - 1.11, p > 0.05) but reduced An. funestus indoor densities by 56% (RR= 0.44 (0.23 - 0.87, p < 0.05)). Houses with eave gaps had 3.3 and 5.5 times more An. gambiae s.l. (RR= 3.3 (2.39 - 4.56, p < 0.05)) and An. funestus ((RR = 5.55 (3.25 - 9.46, p < 0.05)) respectively. Intact screening over windows reduced up to 66% (RR = 0.34 (0.17 - 0.69)) and 83% (RR = 0.17 (0.08 - 0.39)) indoor entry of An. gambiae s.l. and An. funestus respectively. Furthermore, surveillance of wild malaria vectors populations and susceptibility to insecticide resistance demonstrated significant increase in An. funestus densities in 2012 (RR=1.56 (1.33-1.69)) compared to An.gambiae s.l. (p <0.0001). In 2014, the proportion of An. gambiae s.l. catches (67%; 4373/6373) was higher than An. funestus (33%; 2100/6373). PCR results revealed change in relative proportion between the two sibling species of An.gambaie s.l. with a significant decrease in An. gambiae s.s. from approximately 14% (414/2,924) in 2008 to 0% (0/435) in 2014. Insecticide susceptibility tests indicated high resistance in An. funestus against deltamethrin (mortality rate in discriminating dose assay = 87%), lambda cyhalothrin (74%), permethrin (65%), bendiocarb (65%), and DDT (66%). Similarly, An. arabiensis showed insecticide resistance to permethrin (77%), deltamethrin (64%) and lambda cyhalothrin (42%) in 2014. In large screened cages it was demonstrated that adult An. arabiensis can disseminate PPF from clay pots treated with PPF to the aquatic habitats, resulting in 76.5% reduction in adult emergence, with higher mean proportion of adult emerging from untreated chamber, 0.95 (0.56 -1.34) compared to the treated chamber, 0.21 (0.09 - 0.51, p < 0.0001). Treatment of a single clay pot resulted in 58% reduction in adult emergence in six habitats, with mean proportion of 0.34 (0.21 – 0.45) compared to the controls, 0.98 (0.96 – 1.00, p < 0.0001), showing a high level of habitats coverage amplification of the autodissemination event. After treating the walls and ceilings of cattle shelters with PPF, mosquito sterilization resulted in > 95% (89.3 - 102.9%) reduction in adult An. arabiensis production. This research provides evidence on the need of better housing and larviciding to complement LLINs in controlling the remaining malaria transmission transmitted by An. funestus and An. arabiensis. It also demonstrated for the first time that the PPF autodissemination strategy and sterilization of adult females present a promising malaria vector control option for field trial. PPF-autodissemination can be integrated into a vector management toolbox to control outdoor malaria transmission and also target multiple disease-carrying mosquitoes that share aquatic habitats with malaria vectors. These findings highlight the potential of PPF for controlling outdoor and indoor malaria vectors and call for further testing in the field.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Q Science (General) ; RA0421 Public health. Hygiene. Preventive Medicine