Study explains persistent schistosomiasis hotspots in China

A 13-year study led by the Colorado School of Public Health at the University of Colorado Anschutz reveals why a deadly parasitic infection targeted for elimination in China persisted in some areas even after decades of control.

The research, which used artificial intelligence (AI) and classic "shoe-leather" investigations, investigated some of the last pockets of disease in the country. They found that farming practices and unsafe sanitation contributed to disease spread. Additionally, as the region approached elimination, the authors found that disease spread became highly localized. The findings indicate that infectious disease elimination efforts can benefit from shifting towards fine-scale surveillance and household level interventions in the final stages of disease elimination.

The study was published today in PLOS Neglected Tropical Diseases.

Understanding schistosomiasis: A global health threat

Schistosomiasis, a parasitic infection affecting an estimated 200 million people worldwide, causes anemia, fatigue, stunted growth liver damage, and, in some cases, cancer. It is one of a number of "neglected tropical diseases" that are concentrated in low-income, rural communities. Several countries, including China, are trying to eliminate the disease. However, in these areas targeted for elimination, the disease continues to appear in small pockets, threatening public health and national elimination programs.

Even when overall infection rates are low, the disease can persist in some environments that we call hotspots, making the final push to eliminate it the hardest. Our study was designed to understand what happens at the edge of elimination. Our findings highlight that understanding household and environmental risk factors at a very local scale is key to protecting communities and sustaining public health gains globally."

Elizabeth Carlton, PhD, lead author of the study and chair of Environmental and Occupational Health at the Colorado School of Public Health

Long-term fieldwork and AI reveal household risk factors

The study followed villages in southwest China for more than a decade to understand how infection risk changed over time. Researchers in the US and China focused on hotspot villages where the disease persisted despite control efforts. Researchers combined traditional fieldwork including household surveys and environmental assessments with modern artificial intelligence methods. Using AI algorithms, they analyzed patterns across thousands of data points, identifying the most important predictors of infection and how risk shifted from village-level to individual households over time.

Farming practices, unsafe sanitation and domestic animals linked to infection risk

The study found that villages where large areas were dedicated to rice or other crops, where people commonly used human waste as fertilizer, and where fewer households had safe household sanitation had higher infection rates. As infections declined over time, household-level factors including the area of land a family planted, having an improved toilet in the home, and even ownership of cats and dogs became more important (domestic animals can spread the parasite).

The age group most at risk shifted over the course of the study with older adults most affected in later years, reflecting changes in demographics in rural China.

"Community-wide strategies work early in control programs but are not enough near elimination," said Carlton. "Targeted household interventions, including improving sanitation, adjusting farming practices and monitoring domestic animals, are essential to finish the job."

Policy implications: Using household data to accelerate elimination

Public health programs and policymakers in China and other countries attempting to eliminate schistosomiasis are urged to incorporate fine-scale data on agriculture, sanitation and domestic animal ownership to target resources effectively, prevent disease resurgence and accelerate elimination.

"Ending a disease requires adapting strategies as risk becomes localized and integrating human, animal, and environmental data. Our study provides a roadmap to finish the fight against disease, but action is needed now," said Carlton.

This study was conducted through a collaboration between the Colorado School of Public Health at the CU Anschutz and the Sichuan Center for Disease Control and Prevention in Chengdu, China, supported, in part, by the National Institutes of Health.

Other authors on the study include: William W. Zou, Doctoral Student, Environmental and Occupational Health DrPH Program; Elise N. Grover, Senior Research Scientist, Environmental and Occupational Health; and Liu Yang, Sichuan Centers for Disease Control and Prevention, Chengdu, China.