field visits in malawi and zambia

by Hemant Tripathi and Steve Sait (University of Leeds), Akbar Ganatra and Sander Koenraadt (Wageningen University) and Martin Simuunza (University of Zambia)
June 26, 2023

Vector-borne diseases (VBDs) are a major health problem in Africa, exacerbated by the interaction of ecological, climate, and socio-economic factors. These diseases burden humans and livestock, and strain healthcare systems. The occurrence of VBDs is significantly influenced by interactions among agricultural practices, landscape structure, and vectors within and between species interactions. Understanding these interactions can help design effective interventions against these diseases. However, significant knowledge gaps exist in the local as well as landscape-scale understanding of the complex interplay between vectors, pathogens, hosts, and their environment, as well as the effect of changes in farming practices.

As part of the FoSTA-Health project, we carried out a systematic review of the scientific literature, government documentation and public health data sets to identify major patterns and key research gaps. We found that the relationship between landscape structure and the risk of VBDs, particularly those spread by mosquitoes and ticks, is complex and influenced by numerous local and landscape-level factors. These include local species characteristics of hosts and vectors, composition of local ecological communities, farming practices, landscape composition and climatic conditions.

Many studies suggest that diverse, heterogenous landscapes and crop systems typically have lower VBD risks than more homogenous systems. This is due to the presence of alternative hosts in the ecological community (known as the ‘dilution effect’), competition between species, predation by natural enemies, and a variety of habitats that can dilute disease prevalence and impact. Conversely, intensive farming methods, such as irrigation, monoculture, and pesticide use disrupt local biodiversity. This can result in an emergence of resistance among mosquitoes and ticks, and an increase in their populations and breeding sites, influencing the interaction between vectors and non-vectors, and changing disease transmission routes. Additionally, risk displacement can also occur where the burden of disease moves from farms that use pesticides for vector control to those that can't afford such methods.

Additionally, our review revealed a lack of spatially explicit data on disease incidence and risk. The potential of high-resolution remote sensing data for local-scale disease risk mapping remains largely untapped, which hinders the development of targeted disease control strategies. Similarly, our understanding of how specific species interactions at community and meta-community levels, species traits and population density affect disease susceptibility is limited. For example, the role of vector species’ diversity and composition, and animal host density in the spread of tick-borne diseases in livestock remains underexplored.

It is crucial to collect local data on vectors and their interactions with farm practices to understand species dynamics and their impact on VBD transmission. Besides, acknowledging the socio-ecological aspect of farming—including farmers’ knowledge, decision-making, and innovation adoption—is key as these can shape VBD risk. Further, we stress the need for more field research in diverse agricultural settings to improve species interaction and distribution models and enhance VBD risk predictions.

The FoSTA-Health project will adopt this  comprehensive approach to better understand and manage vector-borne diseases. Moreover, we emphasize that adopting a One Health perspective and transdisciplinary approach is critical to understanding the complex factors involved in VBD spread. Strategies should be co-designed with project partners and local communities, ensuring diverse input and practical application. There is also an immediate need for better data collection via capacity building, funding, and collaborations at multiple levels, which will enhance data availability and provide deeper insights into VBD dynamics.

Image courtesy: Stevie Mann- ILRI, Wikimedia (Left) and Shardar Tarikul Islam - (Right)

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