# One health at the last mile: Multi-scale predictors of Schistosoma japonicum infection in southwest China across two decades of control

## TL;DR

This study examines how factors influencing schistosomiasis infection in China changed over two decades, showing shifts in risk from village-level to household-level factors as the disease approached elimination.

## Contribution

The study identifies multi-scale predictors of schistosomiasis infection and how they evolved during reemergence and elimination phases in southwest China.

## Key findings

- Village-level agricultural practices were dominant predictors in the reemergence period, while household and individual factors became more important during the elimination phase.
- High dry crop cultivation combined with poor sanitation amplified infection risk in the elimination period.
- The age group at highest risk shifted from 40-60 to over 80 years of age over the study period.

## Abstract

In China, schistosomiasis is targeted for elimination. As the country approaches elimination, it is critical to evaluate how the dynamics of transmission are changing in remaining pockets of disease. We have been studying areas of schistosomiasis reemergence and persistence in Sichuan, China since 2007. This study used gradient boosting machines to identify key predictors of infection across two periods, 2007–2010, a period when schistosomiasis had reemerged, and 2016–2019, a period when schistosomiasis was approaching elimination. We also evaluated how key predictors of infection have shifted over time and whether combinations of predictors amplified risk. We considered predictors describing agriculture, domestic animals, socio-economic status, water and sanitation infrastructure, and demographics at individual, household and village-level scales. Our re-emergence and elimination models demonstrated strong predictive performances (AUC-PR = 0.92 and AUC = 0.85, respectively). In both periods, a person’s age and village level agricultural practices including the average area of dry crops, rice planted, and night soil use, were among the most influential factors. Village-level factors dominated in 2007–2010, while household and individual predictors increased in predictive importance in 2016–2019. Between 2007–2010 and 2016–2019, there were increases in the importance of household agricultural practices such as the area of dry crops and rice cultivated, and household cat and dog ownership, while the importance of factors describing water and sanitation infrastructure decreased. In the elimination period, our models found the combination of high village dry crop cultivation and lack of improved sanitation amplified infection probability. Our findings suggest adding precision interventions targeting high-risk households on top of existing community-wide measures may accelerate schistosomiasis elimination. Practitioners should consider adding agricultural, sanitation and animal infection data to end-game surveillance programs, while researchers evaluate the consistency of these findings in other low-endemic settings and explore causal pathways to inform adaptive, locally tailored strategies.

Schistosomiasis is a parasitic disease that has been a target of disease control efforts globally, with China aiming to eliminate the disease as a public health problem. In China, disease control efforts have been successful in reducing the spread and prevalence of the disease, though there are remaining pockets of low levels of transmission. Our study compared the most important predictors of schistosomiasis infection risk between two periods, 2007–2010, a period when schistosomiasis had reemerged, and 2016–2019, a period when schistosomiasis was approaching elimination. We found village-level factors were the most important predictors of infection in the earlier and later periods, while household and individual-level increased in importance in the later period. For example, the area rice and other crops cultivated were positively associated with infection. The importance of potential animal hosts such as ownership of cats and dogs also increased over time. We also found that the age of peak disease risk shifted from 40-60 to >80 years of age over our 13-year study period. Our results indicate that the factors behind disease may be changing, potentially due to the selective pressures of decades of disease control and largescale socioeconomic changes such as urbanization.