[National surveillance of in China, 2015-2019].

OBJECTIVE

To analyze the monitoring data of s in the national schistosomiasis surveillance sites of China from 2015 to 2019, so as to understand the changes of snail status in the schistosomiasis-endemic areas of China and to provide the scientific evidence for snail control.

METHODS

According to the requirements of (), national schistosomiasis surveillance sites were assigned in all schistosomiasis-endemic counties (cities, districts) and the potential endemic counties (cities, districts) in the Three Gorges Reservoir areas, and snail status was monitored according to different epidemic types. In endemic areas, snail survey was performed by means of systematic sampling and environmental sampling, and the occurrence of frames with snails and the prevalence of infections in snails were calculated, while in potential endemic areas, the risk of imported snails and snails in floating debris were monitored.

RESULTS

snail survey was performed covering an area of 116 834.16 hm in the national schistosomiasis surveillance of China from 2015 to 2019, with 35 007.62 hm snail habitats identified. A total of 6 908 292 frames were surveyed during the 5-year period, and there were 364 555 frames detected with snails, with a 5.28% mean occurrence of frames with snails. Among 997 508 living snails captured, no infections were detected, and loop-mediated isothermal amplification (LAMP) assay detected 18 positive mixed snail samples. During the period from 2015 to 2019, 147.20 hm emerging snail habitats were identified, with an overall tendency towards a rise seen in the proportion of emerging snail habitats in plain regions with waterway networks (0.12% to 92.00%), a tendency towards a rise followed by decline seen in marshland and lake regions (0 to 96.72%), and a large fluctuation in hilly regions (0 to 88.49%). A total of 831.10 hm re-emerging snail habitats were found in the national schistosomiasis surveillance sites of China from 2015 to 2019, with an overall tendency towards a rise seen in the proportion of re-emerging snail habitats in marshland and lake regions (16.05% to 79.66%), an overall tendency towards a decline seen in hilly regions (19.25% to 81.00%), and a minor fluctuation in plain regions with waterway networks (1.10% to 10.14%). During the 5-year period from 2015 to 2019, a total of 48 656 kg floating debris were captured in 4 surveillance sites in the Three Gorges Reservoir areas, and 2 204 snails were found, with no snails identified.

CONCLUSIONS

The areas of snail habitats tended to be stable in the national schistosomiasis surveillance sites of China during the period from 2015 to 2019, however, there was a gradual rise in the area of snail habitats year by year, and LAMP assay identified positive snail samples, suggesting snail control is far from optimistic in China.