Preplanned Studies: Rapid Assessment on Potential Risks of Schistosomiasis Transmission — 7 PLADs, China, 2019 and 2021

Schistosomiasis was endemic to 12 provincial-level administrative divisions (PLADs) in the middle and lower reaches of the Yangtze River and southern China.Oncomelania hupensis(O. hupensis) was the only intermediate snail host ofSchistosoma japonicum(1). Previous studies had illustrated that the contribution of cattle feces to the transmission of schistosomiasis had accounted for 75% (2). In order to detect these potential risks of schistosomiasis transmission, indicators including distribution and infection rates ofO. hupensisand livestock’s feces aroundO. hupensishabitats were assessed at the beginning of transmission season in the 7 PLADs where schistosomiasis elimination had not achieved the national criteria (3). The rapid assessments were conducted in the spring of 2019 and 2021. TheO. hupensissurvey was performed by means of environmental sampling, and livestock feces samples were collected in surveyedO. hupensishabitats. Loop-mediated isothermal amplification (LAMP) assay and miracidial hatching were used to detect forO. hupensisinfection and livestock’s feces samples, respectively. In 2021, 2 surveyed environments detected nucleic acids of schistosomes amongO. hupensissnails by LAMP assay. Schistosome eggs were found in cattle feces collected from snail habitats both in 2019 and 2021. These results indicated that the distribution and infections ofO. hupensisand livestock’s feces may cause concerns in endemic areas, which also gave an early warning that rapid response measures should be implemented in key environments to eliminate the potential risks of schistosomiasis transmission as soon as possible.

The assessments were conducted in the schistosomiasis endemic areas of Hunan, Hubei, Jiangxi, Anhui, Jiangsu, Sichuan, and Yunnan Provinces. Stratified random sampling was used to select surveyed environments. In each surveyed environment, over 50 square frames of 0.1 m²were used to capture allO. hupensiswithin the frame. Every 10 specimens of capturedO. hupensiswere pooled in 1 centrifuge tube (1 tube for less than 10O. hupensis) for DNA extraction, and DNA extracted from 50O. hupensissamples were pooled for LAMP assay to detectS. japonicum.Surveyed environments with LAMP-tested positiveO. hupensiswere categorized as a positive environment. Livestock’s feces found in surveyedO. hupensisfields were all collected. Stool samples were categorized as positive if schistosome miracidia was detected by the hatching test (3 bottles for 1 sample). The proportion of frames with livingO. hupensisto total surveyed frames, rate of positiveO. hupensishabitats, and positive livestock-feces samples were calculated.

A total of 33 administrative villages in 14 counties of the 7 PLADs were sampled in 2019 and 2021 without duplicate sampled counties (Table 1–2). In 2019, 68O. hupensisinhabited environments were surveyed, in which 41.18% (28/68) environments hadO. hupensiscaptured. Out of the total of 3,115 surveyed frames, livingO. hupensisoccurred in 324 frames. A total of 1,919O. hupensiswere living of all 2,076 captured, and an irrigation ditch in Laoguanju Village (Hubei Province) had the highest number of livingO. hupensisin single frame at 69/frame. The LAMP assay detected no positive environments from all surveyed fields. A total of 56 stool samples were found in 7 sampled counties’ surveyed environments, including 53 (94.64%) cattle-feces samples and 3 (5.36%) sheep-feces samples. A total of 4 cattle-feces sample from a marshland in Minglang Village (Hunan Province) tested positive by miracidial hatching, with a 7.14% (4/56) positivity rate of livestock-feces samples (Table 1).

In 2021, 74O. hupensisinhabited environments were surveyed, in which 50% (37/74) of environments hadO. hupensiscaptured. Of the total of 3,532 surveyed frames, livingO. hupensisoccurred in 292 frames. In addition, of all 1,958O. hupensiscaptured, 1,870 were living. In marshland and lake endemic areas, an irrigation ditch in Lianyi Village (Hubei Province) had the highest number of livingO. hupensisin a single frame at 94/frame. In mountainous and hilly endemic areas, a tobacco field in Yunfeng Village (Yunnan Province) had the highest number of livingO. hupensisin a single frame at 31/frame. The LAMP assay detected 2 positive environments where the nucleic acids of a schistosome were found inO. hupensis, including a marshland in Wufeng Village (Jiangxi Province) and an irrigation ditch in Lianyi Village (Hubei Province), with a 2.70% (2/74) positivity rate ofO. hupensishabitats. A total of 54 stool samples were found in 13 surveyed environments in 9 sampled counties, including cattle feces, sheep feces, and other mammal’s feces, accounting for 42.59% (23/54), 38.89% (21/54), and 18.52% (10/54), respectively. One cattle-feces sample from a marshland in Lianxu Village (Jiangxi Province) tested positive by miracidial hatching, with a 1.85% (1/54) positivity rate of livestock-feces samples (Table 2).