Practical new approaches to delivering biologically rational vector control in the context of conflict, displacement, extreme weather events and other natural disasters
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Date
2023
Authors
Allan, Richard James
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Publisher
University College Cork
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Abstract
Conflicts and extreme weather events have multiplied since the 1960s, disproportionately affecting some regions and displacing escalating numbers of people annually. By 2022, 114 ongoing armed conflicts, mainly in countries with endemic vector borne diseases (VBD), left 274 million people dependent on humanitarian assistance, including 103 million forcibly displaced facing dreadful journeys, often without shelter, followed by years living in camps. The UN predict numbers needing humanitarian assistance will rise to 339 million during 2023.
Extreme events often generate hazardous environmental conditions in which arthropod vectors thrive and human vulnerability to VBD increases. Related morbidity and mortality rates escalate in the early weeks of new humanitarian crises, remaining high until implementation of effective vector control (VC) measures. In the most challenging contexts, disease transmission may continue uncontrolled due to lack of suitable VC tools.
Roll Back Malaria halved annual malaria deaths by 2015, and averted 2 billion malaria cases (2000 to 2021). Distribution of >2.5 billion insecticide treated nets (ITNs) and targeted indoor residual spraying were credited for 69% and 10% of cases averted, respectively. These tools exploit the specialized behaviours of just a few largely nocturnal mosquito species, together with humans’ night-time behaviour in houses, making these very efficient malaria vectors highly vulnerable to control. Mosquito species without this sterotypical behaviour may avoid control and continue to transmit malaria. For homeless displaced people sleeping outside or in flimsy temporary shelters in high malaria burden countries in Africa, standard VC house tools can be poorly adapted. Between 2015 and 2021, annual global malaria deaths rose by 41%; just eleven countries accounted for 80% of these, with eight affected by humanitarian crises.
This thesis covers research investigating the feasibility, acceptability, durability, and effectiveness of existing and new VC measures for suppressing disease transmission throughout the hellish journeys of the forced displaced. The first study compared 12-month performance of Interceptor® LLIN and conventional ITNs amongst returnees to rural villages in Liberia. User-perceived effectiveness drove high (94%) retention and utilization, with 11 >50% reduction of malaria prevalence. Laboratory analysis revealed just 22% total insecticide loss in Interceptor® over 12 months. The durability of the LLINs most commonly distributed in 2000-2011 (Interceptor®, Olyset® and Permanet®) was investigated amongst displaced and host families living in grass and stick shelters and mud huts, during conflict in Chad. Fourteen months post-distribution, standard hole index (STI) categorisation classed 69.5% of LLIN in “poor” or “very poor” condition, with “poor” condition 4.2 times more likely in polyester compared to polyethylene LLINs. Performance of PermaNet® Dumuria, an innovative non-mesh polyester LLIN, with UV protectant, was assessed amongst nomadic people sleeping outdoors in north-east Kenya. Data analysis revealed 95.3% of respondents liked this LLIN at 12 months, with 98.0% retention at 22 months and 97.1% nets in “good” condition (STI); acceptable insecticide levels (WHO definition) were found in 100% and 66.7% of nets after 18 and 22 months outdoor usage, respectively.
Studies exploring an alternative VC option for displaced populations confirmed that temporary shelters constructed fully with novel insecticide-treated plastic sheeting were safe and reduced malaria incidence among young refugee children by 61% in camps in Sierra Leone.
Finally, a randomised cluster trial of durable wall lining (DWL) was carried out amongst Liberian returnees. The DWLs contained Abamectin and Fenpyroximate, never previously used for controlling malaria mosquitoes. DWL installed on internal walls and ceilings of houses in 20 villages resulted in a reduction of malaria 12 months later (p=0.022), although this effect was limited to upland villages. Rapid reduction of bioefficacy after 12 months indicates the need for further research and development.
In conclusion, this thesis helps inform practical and biologically-rational VC planning in different humanitarian crises’ contexts. It provides insights into the overall effectiveness of conventional and practical technical variations on the deployment of insecticide-treated materials to physically shelter crisis victims and target the anthropophagic vectors responsible for most of their night-time malaria exposure. The thesis reviews published work on the need to integrate VC strategies and develop new tools, to control the wider range of 12 insects that then thrive among living conditions associated with newly settled human communities as populations emerge from crisis and either resettle back into their rural homes or move permanently into poor, overcrowded, informal urban settlements.
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Keywords
Conflict , Extreme weather events , Forced displacement , Biologically rational vector control , Natural disasters , Malaria , Vector borne diseases
Citation
Allan, R. J. 2023. Practical new approaches to delivering biologically rational vector control in the context of conflict, displacement, extreme weather events and other natural disasters. PhD Thesis, University College Cork.