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Title: Malaria vector surveillance in the context of enhanced vector control in western Kenya
Author: Abongo, Bernard
ISNI:       0000 0004 8507 1157
Awarding Body: Liverpool School of Tropical Medicine
Current Institution: Liverpool School of Tropical Medicine
Date of Award: 2019
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This thesis describes a series of entomological studies designed to assess malaria vector surveillance in the context of enhanced vector control and altered vectorial system. As malaria vector control efforts are scaled-up and supplemented with new ones, vector populations decline, and behavioural adaptations arise that make surveillance by traditional methods and systems difficult and less informative. The first study assessed the impact of indoor residual spraying (IRS) on the local mosquito population and malaria transmission in a region with high bednet coverage and wide-spread pyrethroid resistance in malaria vectors. Mosquito collections were performed by pyrethrum spray catch (PSC), light trap and human landing collection (HLC). Secondly, a comparison of mosquito surveillance by supervised entomology teams and community-based sampling approach was performed in a region with low mosquito numbers and high bednet coverage. The last study evaluated a novel sampling tool, Host decoy trap (HDT), for collection of outdoor host-seeking mosquitoes. IRS was associated with 88% (p < 0.001) and 93% (p < 0.001) reduction in the population of An. funestus in the intervention areas compared to non-intervention areas as measured by light trap and PSC respectively. Reduction in the numbers of An. arabiensis in PSC was 69% (p=0.006), while no significant difference was detected with light traps (p=0.05). After IRS, An. arabiensis become dominant, 86% and 66% in PSC and light traps respectively while human-biting rates by An. funestus reduced to undetectable levels. No sporozoite infections were detected in the sprayed areas post-IRS and malaria test positivity among febrile patients within IRS areas was lower post- compared to pre-IRS by 44%, 65.03% and 47.42% in Rongo, Uriri and Nyatike health facilities respectively. Community-based sampling collected approximately 90% fewer Anopheles in indoor CDC light trap compared to supervised mosquito sampling schemes. Similar monthly trends in mosquito numbers and sporozoite infection rates, were observed in indoor light trap, outdoor light trap and prokopack aspiration indoor by community-based collectors. In evaluation of HDT, cattle baited trap (HDT-C) collected a nightly mean of 43.2 (26.7-69.8; 95% CI) Anopheles, compared to 5.8 (4.1-8.2; 95% CI) in HLC, while human baited, (HDT-H) collected 0.97 (0.4-2.1; 95% CI), significantly fewer than the HLC. The proportion of An. gambiae was highest in HLC (0.55 ±0.05) followed by HDT-H (0.20 ± 0.09) and least in HDT-C (0.06 ± 0.01). A single application IRS with pirimiphos-methyl resulted in near elimination of An. funestus and a corresponding reduction in malaria test positivity rates among out-patients. Community-based mosquito surveillance offered prospects for extensive, multiple mosquito sampling, but substantially underestimated mosquito numbers. The addition of low cost devolved supervisory system is recommended to enforce compliance and improve data quality. The HDT, on the other hand, offered the prospect of a system to monitor and potentially control An. arabiensis and other outdoor-biting mosquitoes more effectively.
Supervisor: Torr, Steve ; Donnelly, Martin ; terKuile, Feiko Sponsor: United States Agency for International Development ; Medical Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QX 600 Insect control. Tick control ; QX 650 Insect vectors ; WA 395 Health in developing countries ; WC 750 Malaria ; WC 765 Prevention and control