How Removing Aquatic Vegetation Can Help Rural Households Escape Poverty-Disease Traps

Academic Background

In low- and middle-income countries, rural populations face relatively high infectious disease prevalence and low agricultural productivity, which together result in low incomes, creating a poverty-disease trap. This trap reinforces poverty and disease, making it difficult to break the cycle. In Africa, efforts to boost agricultural production through fertilizer use can inadvertently promote the growth of aquatic vegetation, which serves as a habitat for disease vectors. Schistosomiasis, a parasitic disease transmitted by snails, currently infects over 200 million people globally, with 800 million at risk of infection. Traditional control methods rely on mass deworming, but this approach does not eliminate snails and parasites from water bodies, leading to rapid reinfection.

Recent field trials have shown that removing aquatic vegetation can significantly reduce schistosomiasis infection rates, while converting the harvested vegetation into compost can increase agricultural productivity and income. However, this intervention is not widely practiced in the study region of northern Senegal. Therefore, understanding why this intervention works and whether it can be a transferable method to help households escape poverty-disease traps has become a central research question.

Source of the Paper

This paper was co-authored by Molly J. Doruska, Christopher B. Barrett, and Jason R. Rohr, from Cornell University and the University of Notre Dame. It was published on December 17, 2024, in PNAS (Proceedings of the National Academy of Sciences), titled Modeling how and why aquatic vegetation removal can free rural households from poverty-disease traps.

Research Process and Results

Research Process

The study developed a bioeconomic model that integrates a disease ecology model of schistosomiasis infection dynamics with a microeconomic model of agricultural household behavior. The model links agricultural production, poverty, and disease through household decisions on labor allocation, aquatic vegetation harvesting, and fertilizer use.

1. Disease Ecology Submodel: This submodel describes the interactions between schistosomes, aquatic vegetation, and snail populations, and links these populations to human infections. It tracks the dynamics of aquatic vegetation (Ceratophyllum), snails, schistosome larvae (miracidia and cercariae), and infected and susceptible human populations.

2. Agricultural Household Submodel: This submodel describes how households allocate land, labor, and income to maximize their utility. Households increase agricultural productivity by producing food, harvesting aquatic vegetation, and converting it into compost. The model assumes that households cannot fully control the decisions of all members, such as parents being unable to completely prevent children from contacting water, so the dynamics of disease ecology are beyond household control.

3. Model Linkage: The disease ecology submodel and the agricultural household submodel are connected through household infection status and fertilizer use. Infection status directly affects household labor supply and income, while fertilizer use influences aquatic vegetation growth through runoff.

Key Results

1. Effect of Aquatic Vegetation Removal: When households do not harvest aquatic vegetation, the vegetation remains at the system’s carrying capacity, and the snail population increases, leading to high household infection rates. High infection rates limit labor supply, resulting in low income and a poverty-disease trap. However, when households begin harvesting aquatic vegetation, vegetation levels drop significantly, and infection rates decrease, especially for poorer households with less land. This intervention reduces snail habitat and increases compost use, boosting agricultural productivity and income.

2. Impact of Fertilizer Use: Fertilizer use increases agricultural output but also promotes aquatic vegetation growth through runoff, indirectly increasing infection risk. The model shows that fertilizer use is negatively correlated with infection rates, as high infection rates lead to reduced fertilizer use. This suggests that balancing agricultural development and disease control is necessary to break the poverty-disease trap.

3. Sensitivity Analysis: The model conducted sensitivity analyses on parameters such as the effect of fertilizer runoff on vegetation growth, vegetation recolonization rate, vegetation growth rate, and fertilizer price. The results show that the core findings of the model are robust across different parameter values, indicating that aquatic vegetation removal has potential economic and health benefits under various agroecosystem and market conditions.

Conclusions and Significance

By integrating a disease ecology model with a microeconomic model, the study reveals the mechanisms behind the poverty-disease trap and demonstrates how aquatic vegetation removal can help rural households escape this trap by altering the feedback between human and natural systems. The results show that aquatic vegetation removal not only significantly reduces schistosomiasis infection rates but also increases agricultural productivity through compost use, thereby boosting household income.

Scientific and Practical Value

This study provides a theoretical framework for understanding the structural underpinnings of poverty-disease traps and offers a basis for designing ecosystem-based interventions. The results suggest that aquatic vegetation removal is a low-cost, high-impact intervention, particularly suitable for poor communities with limited land. Additionally, the study highlights the importance of considering disease ecology in agricultural development to avoid inadvertently exacerbating disease transmission.

Research Highlights

1. Innovative Model: The study is the first to integrate a disease ecology model with a microeconomic model, providing a structured framework to understand the formation and breaking mechanisms of poverty-disease traps.
2. Practical Application: The study demonstrates how aquatic vegetation removal, as an ecological intervention, can reduce disease infection rates while increasing agricultural productivity, with broad application potential.
3. Policy Implications: The study provides scientific evidence for policymakers, community leaders, and development agencies, suggesting that aquatic vegetation removal be adopted as an effective schistosomiasis control measure and scaled to other similar regions.

Other Valuable Information

The study also estimates the economic benefits of aquatic vegetation removal. By extrapolating the findings from Senegal to all of West Africa, the study estimates an annual economic gain of $138.5 million for the region. This estimate only considers direct productivity gains and reduced workdays lost to illness, excluding long-term benefits from improved child health and education. Therefore, the actual economic benefits could be even higher.

This study not only offers new insights into understanding poverty-disease traps but also provides scientific evidence for designing effective interventions, with significant theoretical and practical implications.