Unconventional thinking: how soil science can join the fight against neglected tropical diseases

By guest contributors John Paul M. Wasan^a and Kishor M. Wasan^b , authors of the recent PLOS NTDs Viewpoint article, Effects of climate change on soil health resulting in an increased global spread of neglected tropical diseases

^aUniversity of Saskatchewan, Canada

^bUniversity of British Columbia, Canada

In 2020, the WHO developed an updated strategy to end all neglected tropical diseases (NTDs) by 2030. Neglected tropical diseases are “poverty-promoting infectious diseases that primarily occur in rural areas and poor urban areas of low-income and middle-income countries”. The document identifies specific targets for the prevention, control, elimination or eradication of NTDs. It also emphasizes that achieving the UN Sustainable Development Goals (such as Clean Water and Sanitation, Sustainable Cities, and Climate Action) is critical to ending NTDs. However, one discipline that may support progress on these goals, but has received less attention, is soil science.

When you think of global health strategies to deter the progression of NTDs, investigating the soil sciences is likely not the first thing that comes to mind. However, soil is much more than just dirt! Soil provides nutrients to fuel crop production, acts as a filter to improve groundwater quality, and serves as a habitat for many organisms  – including NTDs and vectors. For this reason, in our recent viewpoint in PLOS Neglected Tropical Diseases we asked the question: what does soil science offer in the fight against NTDs?

The Link Between NTDs and the Soil Environment

The spread of NTDs is often a result of poor drinking water quality, poor sanitation, or proximity to insect vectors. Poor soil characteristics can interact with these factors to further improve the habitat for the NTD or vector. Conversely, recognizing this risk, we can actively manage soil to reduce the potential for transmission. For example, increased standing water and eutrophication have been shown to increase the prevalence of mosquito vectors. Soil compaction (due to machinery) and crusting (due to erosion) reduce drainage rates and cause water to pool at the surface, increasing habitat for mosquitoes. Likewise, eutrophication (the transport of manure, fertilizers and organic matter into a water body) creates a nutrient-rich environment that favours mosquito development. Yet soil science offers solutions, such as tillage and using plants with high root abundance to promote drainage, as well as buffer strips and riparian areas, which are placed at field and wetland edges to filter off-site flow and reduce nutrient transport. Such techniques are also agriculturally beneficial, as they improve crop performance and minimize nutrient losses.

If we consider soil as a mediator between the influence of climate, precipitation, agriculture and human activity, and the success of certain NTDs and vectors, this may be a source of new strategies to combat NTDs. Further, as soil and land management objectives often align with human health objectives (such as reducing mosquito habitat as discussed above), this presents an opportunity to achieve multiple Sustainable Development Goals simultaneously. Below we highlight a case where soil science is in a unique position to achieve the goal of ending NTDs.

Podoconiosis and Soil Mapping

Podoconiosis (also known as mossy foot) is a form of lymphoedema that causes swelling of the legs and is a result of prolonged barefoot exposure to irritating minerals from red-clay soil with volcanic parent material. It is an NTD which is estimated to affect 4 million people, mostly in tropical Africa as well as in the Americas and Southeast Asia. A major management challenge frequently cited is the lack of comprehensive mapping of the disease. Given that soil characteristics are directly linked to this NTD, soil classification surveys and chemical analysis may provide critical information in mapping and management. For example, the Soil Atlas of Africa published in 2013 provides general classification mapping and other projects have built on this with refined chemical and organic matter mapping. Soil texture and pH have been helpful in recent modelling. However, further research is required, as it has been found that while high pH is correlated with Podoconiosis, the minerals thought to be the cause of the disease are not always correlated with its prevalence. As such, further research by soil scientists into the causal minerals or particles is critical in ending this NTD.

A Challenge to our Readers

Ending all NTDs by 2030 is a very ambitious goal. It requires great investment and rapid advances in research, but perhaps most importantly, partnerships with unconventional professions and disciplines, such as agriculture and soil science. These collaborations may offer new approaches to old problems and accelerate progress towards ending all NTDs. Thus, we ask our readers to consider if there is someone in their community, perhaps someone unconventional, who might offer a unique perspective on the fight against NTDs.

About the authors:

Dr. Kishor M. Wasan most recently served as the Dean and Professor (Retired) of the College of Pharmacy and Nutrition of the University of Saskatchewan, and was associate dean of research and a tenured professor at the University of British Columbia until 2014. Dr. Wasan has extensive involvement in the development of new research and educational programs. He has demonstrated success in leading research initiatives through his many years of independent research at UBC. Wasan was also a Distinguished University Scholar and Canadian Institutes of Health Research/iCo Therapeutics Inc. Research Chair in Drug Delivery for Neglected Global Diseases, continues to be a fellow of the Canadian Academy of Health Sciences, the American Association of Pharmaceutical Scientists, and the Canadian Society of Pharmaceutical Scientists. He is well-known in the post-secondary field for his strengths in research and education curriculum change. He was also the Co-Founder and current Co-Director of NGDI-UBC.

John Paul Wasan works in the Department of Plant Sciences at the University of Saskatchewan, Canada. His research is on invasive plants and soil ecology in grasslands. John Paul has a background in environmental policy, as the chair of the City of Saskatoon Environmental Advisory Committee. He is also the founder of the Reclaim Our Prairie! Initiative, which provides K-12 and community grassland education programs.