Molecular diagnosis of suspected intestinal schistosomiasis in a non-endemic area of Yunnan Province, China.

Background: While Schistosoma japonicum is endemic in the Yangtze River Basin and parts of Yunnan and Sichuan provinces in China, Mangshi City in Dehong Prefecture, Yunnan Province, is not recognized as an endemic area. Between 1996 and 2018, more than 20 suspected schistosomiasis cases were reported in this region. Despite clinical symptoms consistent with S. japonicum infection, no eggs were detected in feces, and the intermediate host Oncomelania hupensis was absent locally. Most patients had no travel history to known endemic areas, leaving the infections unconfirmed.

Findings: Rectal biopsy specimens from four suspected cases, preserved as formalin-fixed paraffin-embedded (FFPE) tissues, were re-examined. Microscopy revealed egg-like structures resembling Schistosoma spp. in the specimens. Due to severe DNA degradation from long-term storage (6-16 years), a micro-library construction method was applied to two samples to enable next-generation sequencing (NGS). Using two independent alignment strategies, multiple sequence reads corresponding to S. japonicum were identified in both samples, providing molecular confirmation of infection.

Conclusions: This study presents the first molecular evidence confirming S. japonicum infection in a non-endemic area of Yunnan Province. The findings highlight the diagnostic potential of combining FFPE samples with NGS to resolve long-standing suspected cases lacking conventional parasitological evidence and underscore the importance of continued surveillance in regions not currently classified as endemic.