Molecular evidence on the presence of Schistosoma japonicum infection in snails along the Yangtze River, 2015-2019.

BACKGROUND: Due to sustained control activities, the prevalence of Schistosoma japonicum infection in humans, livestock and snails has decreased significantly in P. R. China, and the target has shifted from control to elimination according to the Outline of Healthy China 2030 Plan. Applying highly sensitive methods to explore the presence of S. japonicum infection in its intermediate host will benefit to assess the endemicity or verify the transmission interruption of schistosomiasis accurately. The aim of this study was to access the presence of S. japonicum infection by a loop-mediated isothermal amplification (LAMP) method through a 5-year longitudinal study in five lake provinces along the Yangtze River. METHODS: Based on previous epidemiological data, about 260 villages with potential transmission risk of schistosomiasis were selected from endemic counties in five lake provinces along the Yangtze River annually from 2015 to 2019. Snail surveys were conducted in selected villages by systematic sampling method and/or environmental sampling method each year. All live snails collected from field were detected by microscopic dissection method, and then about one third of them were detected by LAMP method to assess the presence of S. japonicum infection with a single blind manner. The infection rate and nucleic acid positive rate of schistosomes in snails, as well as the indicators reflecting the snails' distribution were calculated and analyzed. Fisher's exact test was used to examine any change of positive rate of schistosomes in snails over time. RESULTS: The 5-year survey covered 94,241 ha of environment with 33,897 ha of snail habitats detected accumulatively. Totally 145.3 ha new snail habitats and 524.4 ha re-emergent snail habitats were found during 2015-2019. The percentage of frames with snails decreased from 5.93% [45,152/761,492, 95% confidence intervals (CI): 5.88-5.98%] in 2015 to 5.25% (30,947/589,583, 95% CI: 5.19-5.31%) in 2019, while the mean density of living snails fluctuated but presented a downward trend generally from 0.20 snails/frame (155,622/761,492, 95% CI: 0.17-0.37) in 2015 to 0.13 snails/frame (76,144/589,583, 95% CI: 0.11-0.39) in 2019. A total of 555,393 live snails were collected, none of them was positive by dissection method. Totally 17 pooling snail samples were determined as positives by LAMP method among 8716 pooling samples with 174,822 of living snails, distributed in 12 villages of Hubei, Hunan, Jiangxi and Anhui provinces. The annual average positive rate was 0.41% (95% CI: 0.13-0.69%) in 2015, 0% in 2016, 0.36% (95% CI: 0.09-0.63%) in 2017, 0.05% (95% CI: 0-0.16%) in 2018, 0.05% (95% CI: 0-0.15%) in 2019, respectively, presenting a downward trend from 2015 to 2019 with statistical significance (χ2 = 11.64, P < 0.05). CONCLUSIONS: The results suggest that S. japonicum infection still persisted in nature along the Yangtze River and traditional techniques might underestimate the prevalence of schistosomiasis in its intermediate hosts. Exploring and integrating molecular techniques into national surveillance programme could improve the sensitivity of surveillance system and provide guidance on taking actions against schistosomiasis.

[Investigation on endemic situation of schistosomiasis in infection-controlled regions in Anhui Province].

OBJECTIVE: To understand the epidemic situation of schistosomiasis in 27 counties (cities, districts) that reached the criteria of schistosomiasis infection controlled in Anhui Province. METHODS: According to the requirement of The National Assessment Scheme of Schistosomiasis, 81 administrative villages where the schistosomiasis epidemic situation was relatively heaver in above-mentioned 27 counties (1 village per town, 3 towns per county) were sampled and investigated. RESULTS: From 2012 to 2014, 81 villages were investigated, and 34,293 residents received the serum examinations, and 1,086 were positive with a positive rate of 3.17% (0.65%-9.58%), and the positives received stool examinations and the average stool positive rate was 0.37% (0-4.0%). The calculated prevalence of human infection was 0.01%. A total of 3 057 domestic animals were investigated including 438 cattle, 2,550 sheep, and 69 other animals, and no infections were detected. A total of 11,261 living Oncomelania hupensis snails were collected and detected, but no schistosome infected snails were found. Before this investigation, no infected snails were detected for more than 2 years [average 2.3 (2-6) years], and no acute schistosome infection cases were found for more than 2 years [average 4.9 (2-9) years]. CONCLUSION: The infection rates of schistosomiasis in residents and domestic animals are relatively low, and no schistosome infected snails are found in the regions.