Human Decoy Trap; operational and social acceptability of novel tool to improve surveillance and control of mosquitoes and other disease vectors

Lead Research Organisation: University of Greenwich
Department Name: Agriculture Health & Environment, FES

Abstract

Malaria infects over 200 million people every, mostly in sub-Saharan Africa. Nearly half a million people died from the disease in 2015, the majority of deaths being in children under the age of five. The malaria parasite is spread by infected mosquitoes and the most effective way to monitor the disease is to monitor populations of these mosquitoes. However, current tools for sampling malarial mosquitoes are time-consuming and labour intensive, making them expensive and difficult to standardize. Accordingly, data between countries and regions cannot be reliably compared.
To solve this problem, we have developed a mosquito trap that exploits the blood-seeking behaviour of mosquitoes by mimicking the sensory stimuli that a mosquito follows when searching for a person to bite. These include the look, smell and temperature of warm-blooded hosts. We have incorporated these stimuli into a trap that lures mosquitoes towards it and then captures them when they land.
Our project will test this "Human Decoy" Trap against current methods used in mosquito monitoring to determine whether the Human Decoy Trap can overcome the limitations of existing tools. We will evaluate if Human Decoy Trap catches are suitably similar to those of current traps in terms of numbers of mosquitoes and other important data related to malaria that can be extracted from mosquitoes caught by traps, such as the proportion of caught mosquitoes infected with malaria parasites. Over 90 countries, mostly low and middle income, are malaria-endemic. We will work in Burkina Faso, Benin and Cameroon, three West African countries where malaria causes thousands of deaths every year, but differing in intensity and seasonality of transmission and with different mosquito species involved. This will help us to understand whether there are differences in trap performance in a wide range of malaria settings. In addition, we will work with end-users of the trap, namely local communities, public health operatives and field technicians, to better understand their perspectives and needs regarding mosquito sampling and control. During the course of the project, we will use data we collect to optimize and improve the trap's performance and design. This will help us to develop a commercial prototype that is effective and acceptable to end-users, maximising the likelihood the trap will be adopted into the communities and sectors that need it the most.
Longer-term, we envision a version of the Human Decoy Trap that can be deployed as a mosquito control tool. The most effective way of controlling malaria is to reduce the number of infective mosquito bites a person receives. This is currently achieved by providing people with insecticide-treated bed nets to protect them from bites whilst they sleep and spraying the walls inside houses thus killing mosquitoes that rest there. However, neither of these options protects people from mosquitoes that may bite them outdoors during the day or just before they go to bed at night. Data from this current project will be used to provide preliminary evidence for the suitability of the Human Decoy Trap as a control tool that is specifically targeted at malaria mosquitoes biting outdoors, which may also be effective against other species of mosquitoes that can carry other infectious diseases, such as dengue fever, chikungunya and Zika viruses.
Such an improved sampling method would enhance the quality of data necessary for efficient targeting and evaluation of malaria control intervention activities and reduce the cost of collecting it. A successful outdoor mosquito control device would help to reduce the population of infected mosquitoes that cause malaria. Ultimately, the combined effect of these tools would be a reduction in the human suffering and death caused by malaria to millions of people every year and an improvement in the social and economic prospects of the 3.2 billion people living at risk of malaria.

Technical Summary

Current vector monitoring tools have not been standardised to sample effectively indoors and outdoors and epidemiologically relevant metrics do not index well against the gold standard Human Landing Catch (HLC). Additionally, the HLC method is increasingly prohibited as it exposes field technicians to pathogens via potential mosquito bites. We have developed a behaviour-based mosquito trap, using olfactory, visual and thermal stimuli to attract host-seeking female mosquitoes. The Human Decoy Trap (HDT) catches mosquitoes on an adhesive surface as they land, preliminary data showing HDT catches up to 10 x more Anopheles mosquitoes than HLCs and up to 5 x the number of other mosquito genera. These results indicate the HDT could be used for monitoring and suggests potential for an outdoor mosquito control method.
We will test the HDT to determine how well it samples mosquito diversity, abundance, parasite rate and age in comparison to the HLC, CDC Light Trap and Suna Trap. We will compare results indoors, where the majority of malaria transmission takes place, and outdoors, where we have a poor understanding of transmission, and throughout the seasons in rural savannah and rice irrigation areas (Burkina Faso), coastal urban communities (Benin) and a low seasonal transmission setting (Cameroon), to provide data for comparison of trap performance in a range of malaria settings. We will conduct a Participatory Technology Assessment with field technicians and at-risk communities to understand perceptions and needs regarding mosquito monitoring and control tools and acceptability of the HDT. This will provide design recommendations for future iterations of the trap, which can be incorporated into a standardised prototype to be developed with a commercial partner, enhancing the likelihood of successful adoption of the HDT for basic vector research and applied surveillance, and providing preliminary data for the role of the HDT as an outdoor-based mosquito control device.

Planned Impact

Immediate impacts of the new Human Decoy Trap will be to improve malaria vector monitoring by enhancing data quality (accuracy, reproducibility) and collection (efficiency, cost, ethics). National Malaria Control Programs (NMCPs) use vector surveillance to collect epidemiological indicators and assess interventions, yet surveillance tools in use are inadequate. Urgent demand for standardised, ethically acceptable alternatives means that the outcomes of our project will be of immediate and direct relevance to NMCPs in all 95 malaria-endemic countries. Potential to reduce the operational burden on LMIC health systems and enhance the quality of malaria/NTD data is expected, ultimately, to improve control interventions (e.g. spraying campaigns) and to strengthen early detection of potential issues (e.g. emerging insecticide resistance; increased outdoor blood-feeding), locally and nationally.
Beyond the project lifetime the major contributions to scientific advancement will be standardised traps to assess crucial vector-host interactions (e.g. extent of indoor/outdoor-feeding by malaria mosquitoes) without methodological biases skewing results. This knowledge, alongside insecticide-resistance profiles of these populations, will have major positive consequences for the long-term feasibility of vector control by bed nets and indoor spraying; responsive operational impacts are anticipated within public health programmes.
Economic and social impacts will include a standardised commercial mosquito trap and community-produced versions of the trap. Specific economic impacts arising from prototype development derive from material procurement, manufacturing, assembly and distribution, with commercial relationships between the UK and Germany continuing after the project. The commercial version is intended for public health and research purposes. In parallel, the trap will benefit communities at risk of malaria if they are able to produce versions from locally-available materials. This will see impacts including localised economic activity and skills development in LMICs, with longer-term public empowerment to contribute to health monitoring and, potentially, civic ownership and production of mosquito control tools. The potential to impact enterprise growth and positively advance public understanding of infectious disease issues will contribute to economic and social improvements in LMICs.
Long term impacts of an outdoor mosquito control tool based on the concept of the Human Decoy Trap are likely to emerge with groups seeking innovative mosquito control technologies, such as IVCC and RBM's Vector Control Working Group. We foresee additional expertise from these groups feeding into trap modifications to control mosquitoes, with the potential to reduce cases of malaria and other mosquito-borne NTDs where traditional indoor-based approaches do not work. Complementing the main indoor-based vector control methods with an outdoor killing trap has the potential to reduce 214 million cases of malaria/year and associated ~500,000k deaths, lost productivity (economic growth penalty of malaria is ~1.3% of national GDP) and impeded social development (e.g. school absenteeism, disability-adjusted life years). In parallel with applicability to other mosquito-borne NTDs, these impacts could ultimately reach 2.5 billion people at risk of vector-borne diseases.
Intrinsic to our project is working with at-risk communities. Encouraging community engagement and promoting similar approaches in subsistence agriculture and local public health sectors opens the possibility of community-led integrated pest/vector management, creating positive impacts for human, environmental and agricultural/ livestock health, broadening the potential for positive health/environmental (e.g. reduced insecticide residues with reduced incidence of disease vectors), economic (e.g. improved yields) and societal (e.g. community self-governance and sustainability) impacts.

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