The Epidemiology of Schistosomiasis Reinfection and Reemergence in Sichuan, China: Implications for Surveillance and Intervention

Abstract

Treatment can yield rapid reductions in schistosomiasis infections and morbidity, but sustained control of this water-borne parasitic infection has proven challenging. A better understanding of the epidemiology of schistosomiasis following chemotherapy-based control is urgently needed to inform the design of surveillance systems and interventions in post-control regions.

The research presented here documents the reemergence of schistosomiasis in Sichuan Province, China, evaluates surveillance methods for monitoring schistosomiasis-induced morbidity, using ultrasound, and schistosomiasis reemergence, and examines village-level characteristics that may promote schistosomiasis transmission. Research was conducted in a region where praziquantel-based control was ongoing, using a five-year longitudinal study, and in regions where schistosomiasis reemerged five to fifteen years after human infections were controlled, using a cross-sectional survey of 53 villages.

Reinfection following treatment was common in endemic regions, and widespread human and bovine infections were documented in the reemerging areas. Two commonly used surveillance methods, surveys for Schistosoma japonicum-infected snails and acute schistosomiasis case reporting greatly underestimated the extent of reemergence. Methods that targeted high-risk human populations had high sensitivity. Village-level characteristics that promoted the distribution of S. japonicum eggs, including the use of human waste as an agricultural fertilizer (night soil) and the density of bovines, predicted human infection status. Infection intensities were low in the reemerging region.

Areas where night soil use or bovine ownership are common may be primed for reemergence, providing crucial links in the schistosome life cycle that can promote S. japonicum infections. Interventions and surveillance methods that target populations in high-risk environments may aid in interrupting schistosomiasis transmission and permanently reducing morbidity.