[Application of space-time scan statistics in the analysis of spatial and temporal distribution of Oncomelania hupensis snails in Gaoyou County, Jiangsu Province].

OBJECTIVE: To investigate the distribution features of Oncomelania hupensis infested areas in Gaoyou County so as to formulate surveillance and intervention strategies. METHODS: A database was established through collecting data of the snail infested areas during 1970-2009 in the County. The data were input into SaTScan 9.2 software for spatial-temporal cluster analysis to determine the spatial and temporal cluster of the snail habitats. The results were displayed by ArcGIS 10.1 software. RESULTS: There were historically 720 snail habitats in the County in 1970-2009 including 521 in plain region with water networks and 199 in lake & marshland region. Those in water networks covered an area of 456.62 ha distributing mainly in the northern towns/townships of the County, and the latters distributed in the Xinmin Beach between Gaoyou Lake and Shaobo Lake, and Qiaojian Beach close to Tianchang County of Anhui Province with an area of 4 495.75 ha. The spatial-temporal cluster analysis revealed that among all the historical snail habitats, there were two prominent spatial-temporal clusters with a relative risk of >3. One cluster appeared in Xinmin Beach in 1983-2002 and another one located in the north of Gaoyou in 1970-1973. Separate analysis was performed by the regions of water network or lake & marshland, indicating 2 clusters in each of the regions. During 1970-2009, 244 snail habitats were newly found in the County with 130 in water network region and 114 in lake & marshland region. Again, the spatial-temporal cluster analysis displayed 2 prominent clusters. By separate analysis, 2 clusters existed in each of the regions. CONCLUSION: The space-time scan statistics can be applied in detecting the cluster of snail infested areas in two dimensions, which will provide information for guiding specific measures of surveillance and control.

[Further study on possibility of diffusion of Oncomelania hupensis with water in river channels of the east route of South-to-North Water Diversion Project].

OBJECTIVE: To study the drifting law of floats and potential risks of Oncomelania hupensis diffusion in the water diversion rivers of the east route of South-to-North Water Diversion Project. METHODS: The O. hupensis snails in the river channels were monitored by the salvage method and snail luring method with rice straw curtains, and the diffusion possibility of snails along with water was assessed through the drift test of floats with GPS. RESULTS: In the flood seasons from 2006 to 2013, totally 8 338.0 kg of floats were salvaged, and 2 100 rice straw curtains were put into water in the Li Canal and Jinbao shipping channel, but no Oncomelania snails were found. The drift test of floats with GPS before water diversion showed that the flow velocity on water surface (northbound) was 0.45 m/s, the average drift velocity of the floats was 0.56 - 0.60 m/s, and the average drift distances each time were 999.70 - 1 995.50 m in the Gaoshui River section, while there were no obvious drift in Jinbao shipping channel section. During the water diversion period, the flow velocity on water surface (northbound) was 0.45 m/s, the average drift velocity of the floats was 0.35 - 0.41m/s, and the average drift distances each time were 1 248.06 -1 289.44 m in the Gaoshui River, while in Jinbao shipping channel section, the flow velocity on water surface was 0.28 m/s, the average drift velocity of the floats was 0.25 - 0.27 m/s, and the average drift distances each time were 477.76 - 496.38 m. The drift test showed that the floats gradually closed to the river bank as affected by water flow, wind direction and ship waves, when blocked by the reeds, water plants or other obstacles, and they would stopped and could not continue to drift without outside help. CONCLUSIONS: There are no Oncomelania snails found in the river channels of the east route of South-to-North Water Diversion Project. The drifting distance of the floating debris along with the water is restricted by the flow rate and shore environment.

[Surveillance of endemic situation of schistosomiasis in Gaoyou sections in east route of South-to-North Water Diversion Project before water transfer].

OBJECTIVE: To understand the endemic situation of schistosomiasis and the distribution of Oncomelania hupensis snails in Gaoyou sections in the east route of the South-to-North Water Diversion Project before water transfer. METHODS: The Grand Canal, the Sanyang River and the range of 3 kilometers of both sides of the rivers were chosen as the surveillance area in the Gaoyou sections in the east route of the South-to-North Water Diversion Project, and the Gaoyou Lake area adjacent to the east route was also chosen as the surveillance area. The human and livestock schistosomiasis and Oncomelania hupensis snails were monitored by the conventional method. Three underwater snail surveillance sites were set up in the Grand Canal and the Sanyang River respectively, and the net salvage method and the method of attracting snails with rice straw curtains were used to survey the snails underwater in the surveillance sites. RESULTS: The schistosome infected snails, the human and livestock schistosomiasis were not found in the Gaoyou sections in the east route of the South-to-North Water Diversion Project from 2006 to 2012. The snail areas were on the decline in the Grand Canal. The snail was not found in the Sanyang River. A total of 270 kg floatage was refloated and 720 pieces of rice straw curtains were placed in the surveillance sites, and there were no snails in the floatage and the rice straw curtains. CONCLUSION: There is no evidence showing that the snails spread to northward in the Gaoyou sections in the east route of the South-to-North Water Diversion Project.

[Study on surveillance and early-warning system of schistosomiasis in first phase of east route of South-to-North Water Diversion Project. III. Indexes of surveillance and early-warning and risk assessment].

OBJECTIVE: To establish the index system of surveillance and early-warning on schistosomiasis and to provide the scientific basis for risk assessment and emergency plan in first phase of east route of South-to-North Water Diversion Project. METHODS: The Delphi method and the multidimensional synthetic evaluation were used in the evaluation of indexes of surveillance and early-warning on schistosomiasis in the east route of the project. RESULTS: There were 53 indexes evaluated in the index system, and among them, there were 3 first grade indexes, 10 second grade indexes and 40 third grade indexes. The indexes on Oncomelania snails were the most important. According to the habitation position of snails, the four grades on surveillance and early-warning of schistosomiasis were established in the east route. The grade I of the early-warning meant that snails crossed the first level of the pumping station. The grade II meant that snails crossed N 32 degrees 54'. The grade III meant that snails crossed N 33 degrees 03' or Jinhu pumping station. The grade IV meant that snails crossed N 33 degrees 15' or Hongze Station. Other 4 indexes on schistosome infection in people and livestock were confirmed as indicative indexes. According to the relationship among the indexes, the evaluation methods were determined on the risk of schistosomiasis transmission. CONCLUSIONS: The index system of surveillance and early-warning and the methods of risk assessment of schistosomiasis have been confirmed in first phase of east route of South-to-North Water Diversion Project. The primary index is related to snails and the supplementary is related to schistosome infection in people and livestock in the system.

[Investigation on HBsAg carrier rate of population in schistosomiasis transmission-interrupted area of Gaoyou City, 2010].

A total of 500 residents in a schistosomiasis transmission-interrupted area, Maogang Village of Gaoyou City were detected simultaneously for the infection status of schistosome and HBV, and the results showed that there was no significant difference between the HBsAg carrier rates of residents with and without the history of schistosomiasis, but the HBsAg carrier rates in some population were high, which needs more concern.

[Surveillance of Oncomelania hupensis snails in Baoying and Gaoyou sections of Li Canal in east route of South-to-North Water Diversion Project].

OBJECTIVE: To understand the distribution and diffusion of Oncomelania hupensis snails in the Baoying and Gaoyou sections of the Li Canal in the east route of the South-to-North Water Diversion Project. METHODS: The retrospective survey method was used to investigate the distribution and diffusion of snails in the Baoying and Gaoyou sections of the Li Canal, the conventional survey and the methods of salvage of water and attracting snails were used to detect the distribution of snails in river banks and water. RESULTS: The earliest findings of snails in the Gaoyou section of the Li Canal was in 1955, the northernmost distribution of snails was Dilong ferry at the west dam and east slope of the Li Canal. The dynamic surveillance in the Gaoyou section of the Li Canal from 2001 to 2010 showed that the snail status was of low density and low fluctuation of area, and the distribution range was 119 degrees 24' 36" -119 degrees 25' 34", 32 degrees 48' 30" -32 degrees 54' 05". From 2006 to 2010, the snails were not found by the methods of salvage of water and attracting snails in the surveillance in the Baoying and Gaoyou sections of the Li Canal. CONCLUSIONS: So far, there is no evidence showing that the snails spread to northward in the Li Canal, however, it is still necessary to carry out the surveillance of snails and schistosomiasis in the east route of the South-to-North Water Diversion Project.