Spatio-temporal pattern of schistosomiasis in Anhui Province, East China: Potential effect of the Yangtze River - Huaihe River Water Transfer Project.

Anhui Province has been one of typical epidemic areas of schistosomiasis in East China as a wide range of large lake and marshland regions provide an ideal environment for growth and reproduction of the intermediate snail host. With the completion of the Yangtze River-Huaihe River Water Transfer Project (YHWTP), launched by the end of 2016, the epidemic areas are expected to expand and controlling schistosomiasis remains a challenge. Based on annual surveillance data at the county level in Anhui for the period 2006-2015, spatial and temporal cluster analyses were conducted to assess the pattern of risk through spatial (Local Moran's I and flexible scan statistic) and space-time scan statistic (Kulldorff). It was found that schistosomiasis sero-prevalence was dramatically reduced and maintained at a low level. Cluster results showed that spatial extent of schistosomiasis contracted, but snail distribution remained geographically stable across the study area. Clusters, both for schistosomiasis and snail presence, were common along the Yangtze River. Considering the effect of the ongoing YHWTP on the potential spread of schistosomiasis, Zongyang County and Anqing, which will be transected by the new water-transfer route, should be given a priority for strengthened surveillance and control. Attention should also be paid to Guichi since it is close to one of the planned inlets of the YHWTP.

[Trend analysis of schistosomiasis endemic situation in Anhui Province from 2004 to 2014].

OBJECTIVE: To analyze the changes of schistosomiasis endemic situation in Anui Province from 2004 to 2014, so as to provide the evidence for formulating "The thirteenth five year" schistosomiasis control plan. METHODS: The information for schistosomiasis control and the data of the endemic surveillance of schistosomiasis were collected and analyzed for the changes of schistosomiasis endemic situation in Anhui Province from 2004 to 2014. RESULTS: The Oncomelania hupensis snail areas presented on a rising trend, and reached to the largest area with about 3.1 billon m2in 2011. However, the snail areas decreased from 2012, and reduced by 10.55% in 2012 compared with the areas in 2011, and reduced to the lowest level in 2014 in recent 10 years. The density of living snails presented a fluctuation situation from 2004 to 2008, and on a decreasing trend from 2008, and the density of living snails was below 1 snail/0.l i2 after 2011. The infection rate of snails remained stagnant state from 2004 to 2011, and decreased rapidly in 2012, and no schistosome infected snails were found in 2013 and 2014. The schistosome infection rate of residents decreased gradually, and the number of acute schistosomiasis was under 50 cases with scattered distribution after 2006, and no acute cases occurred in 2013 and 2014. The infection rate of livestock was above 1% from 2004 to 2011, and reduced to 0.55% in 2012, and it was the first time that the infection rate of livestock was lower than that of residents in the same year in 2014. The progress for achieving the goal of schistosomiasis transmission control accelerated after 2011, and the number of counties that reached the standard of schistosomiasis transmission controlled from 2012 to 2014 was 4, 9 and 14 and the number of townships was 33, 76 and 32, respectively. CONCLUSION: Schistosomiasis control has achieved remarkable effectiveness in Anhui Province, but there still exists hard work to consolidate the achievement and reach schistosomiasis transmission interrupted.

[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.

[Spatial-time cluster analysis of distribution of schistosomiasis in Jiangling County].

OBJECTIVE: To analyze the spatial-time distribution characteristics of schistosomiasis in Jiangling County, Hubei Province from 2006 to 2011. METHODS: The surveillance data of schistosomiasis of Jiangling County from 2006 to 2011 were collected, and a spatial database was established. The spatial-time permutation cluster analysis was performed by SaTScan 9.1.1 to detect the spatial-time cluster areas of schistosomiasis, and a risk map was drawn by ArcGIS 10.0. RESULTS: Compared to 2006, the infection rates of human, cattle and Oncomelania hupensis snails decreased by 47.67%, 93.34% and 52.41%, respectively in 2011. The space-time permutation clustering analysis of the infection rates of human, cattle and snails showed 4, 3 and 4 clusters, respectively, and all the clustered areas were distributed in inner embankment areas. CONCLUSIONS: From 2006 to 2011, the schistosomiasis endemic situation presents a decline trend in Jiangling County. The detected cluster areas are the important areas for schistosomiasis control. The space-time permutation statistics could be used in the analysis of endemic situation of schistosomiasis.

Fine scale Spatial-temporal cluster analysis for the infection risk of Schistosomiasis japonica using space-time scan statistics.

BACKGROUND: Marching towards the elimination of schistosomiasis in China, both the incidence and prevalence have witnessed profound decline over the past decades, with the strategy shifting from morbidity control to transmission control. The current challenge is to find out hotspots of transmission risk for precise targeted control in low-prevalence areas. This study assessed the risk at the village level, using the spatial and temporal characteristics of Schistosomiasis japonica in Anhui province from 2006 to 2012. METHOD: The comprehensive database was generated from annual surveillance data at village level in Anhui province between 2006 and 2012, comprising schistosomiasis prevalence among humans and cattle, occurrence rate of infected environments and incidence rate of acute schistosomiasis. The database parameters were matched with geographic data of the study area and fine scale spatial-temporal cluster analysis based on retrospective space-time scan statistics was used to assess the clustering pattern of schistosomiasis. The analysis was conducted by using SaTScan 9.1.1 and ArcGIS 10.0. A spatial statistical modelling was carried out to determine the spatial dependency of prevalence of human infection by using Geoda 1.4.3. RESULT: A pronounced decline was found in the prevalence of human infection, cattle infection, occurrence rate of environment with infected vector snails and incidence rate of acute schistosomiasis from 2006 to 2012 by 48.6%, 71.5%, 91.9% and 96.4%, respectively. Meanwhile, all 4 indicators showed a statistically significant clustering pattern both in time and space, with a total of 16, 6, 8 and 4 corresponding clustering foci found respectively. However, the number of clustering foci declined with time, and none was found after year 2010. All clustering foci were mainly distributed along the Yangtze River and its connecting branches. The result shows that there is a direct spatial relationship between prevalence of human infection and the other indicators. CONCLUSION: A decreasing trend in space-time clustering of schistosomiasis endemic status was observed between 2006 and 2012 in Anhui province. Nevertheless, giving the complexity in schistosomiasis control, areas within the upper-stream of Yangtze River in Anhui section and its connecting branches should be targeted for effective implementation of control strategies in the future.

[Survey of endemic situations in schistosomiasis transmission controlled or interrupted regions in Anhui Province].

OBJECTIVE: To understand the variation rules of schistosomiasis endemic situation before and after schistosomiasis transmission controlled or interrupted, so as to provide the evidence for the consolidation of control achievements. METHODS: In Anhui Province, 3 counties reaching the criteria of schistosomiasis transmission controlled or interrupted were selected and their historical endemic data were collected and analyzed statistically from 10 years before the schistosomiasis transmission controlled to 2008. RESULTS: In Tianchang City, the Oncomelania hupensis snail area was 3.54 hm2 in a part of the lake marshland in the year reaching the criteria of transmission controlled (1998), and no snails were found in the year of transmission interrupted (2008). No stool-test-positive resident was detected except there were 58 acute schistosomiasis cases in 1993, and the sero-test-positive rate of local residents remained at low levels (0-1.55%). In Taihu County, the snail area was 0.84 hm2 accounting for 0.06% of its historical accumulative snail areas in the year of transmission controlled (1971) , and no snails were found three years before the transmission interrupted (1983). However, the schistosomiasis endemic rebounded 12 years later (1995), there was an outbreak of acute schistosome infections (73 cases), and the snail area increased again to 133.7 hm2 accounting for 2.91% of historical accumulative snail areas. After that, the snail area kept on rising and the infection rates of residents and bovine remained higher than 1%. In Guangde County, the snail area was 32.4 hm2 accounting for 1.90% of its historical accumulative snail areas in the year of transmission controlled (1995). After that, the snail area increased progressively, and the schistosomiasis endemic rebounded and there were acute schistosome infections 5 years later. The Spearman tests showed that the sero-test-positive rate (Tianchang City) and the stool-test-positive rates of residents and bovine (Taihu County) had positive correlations with the snail areas (r = 0.582, 0.401, 0.596, all P < 0.05). CONCLUSION: The snail status is a key for the consolidation of schistosomiasis transmission controlled and interrupted. Therefore, a valid surveillance system of snail situation should be established as quickly as possible.

[Application of space-time scan statistics in early warning of distribution of schistosome infected Oncomelania hupensis snails].

OBJECTIVE: To explore the application of space-time scan statistics in the early warning of distribution of schistosome infected Oncomelania hupensis snails. METHODS: The data of distribution of infected snails in Anhui Province from 2006 to 2012 were collected, and a spatial database was established by ArcGIS 9.3. The prospective spatial-temporal cluster analysis was done by SaTscan 9.1.1 at the village level. RESULTS: Four space-time clusters, which were distributed over the Yangtze River and its branch rivers, were detected. CONCLUSION: The space-time scan statistics could detect the distribution of infected snails early, and the space-time clusters found were the key and difficult points of schistosomiasis control in Anhui Province.

[Spatial-temporal analysis on the distribution of infected snail at the village level in Anhui province, 2006-2012].

OBJECTIVE: The characteristics of spatial-temporal distribution on infected snails were analyzed at the village level in Anhui province, 2006-2012. METHODS: Data on the distribution of infected snails from 2006 to 2012 in Anhui province was collected. Spatial database was established by ArcGIS 9.3. Retrospective spatial-temporal cluster analysis was done by SaTScan 9.1.1 at the village level. RESULTS: Eight areas with increased risk and distributed along the upstream to downstream of Yangtze and connecting branch rivers, were found having infected snails, from 2006 through 2012, including one area in 2006, five in 2006-2008, one in 2007-2009 and one in 2009-2011, respectively. Proportion on the number of areas with infected snails decreased from 6.2% in 2006 to 0.5% in 2012. CONCLUSION: The spatial-temporal distribution of infected snail was not random but there appeared significant clusters. The trend seemed to be declining in Anhui province, between 2006 and 2012. Areas being detected as snails positive were important for the schistosomiasis control program to be carried out in Anhui province.

[Application of multi-temporal China-Brazil Earth Recourses Satellite-02 data on surveillance of dynamic changes of water body of rivers and Oncomelania snail habitats in Anxiang County].

OBJECTIVE: To study the dynamic changes of the water body of rivers and Oncomelania snail habitats by using multi-temporal China-Brazil Earth Recourses Satellite-02 images taken in Anxiang County so as to establish the correct procedure for selecting images. METHODS: CBERS-02 images were collected on 20th December 2003, 10th February 2004, 10th April 2004, 19th June 2004, 10th August 2004 and 27th October 2004. Then the water body information from the study areas based on NDWI was extracted and the areas of water body were calculated to determine the images. RESULTS: The dynamic changes of the water body conformed to the rules of "water in summer and land in winter". Because of the rise of water, the water area in July was the biggest and the water area began to decline from August. The water area in April was the smallest. Then the wet season and the dry season should be June and April. CONCLUSION: The multi-temporal CBERS-02 images could be used to surveillance the dynamic changes of the water area and helpful in choosing the right images of the wet season and dry season.

[Evaluation of mid-term effectiveness of medium-and-long-term programme for prevention and control of schistosomiasis in Anhui Province].

OBJECTIVE: To evaluate the mid-term effectiveness of the medium-and-long-term programme for prevention and control of schistosomiasis in Anhui Province. METHODS: In the programme, the comprehensive measures were carried out, including the schistosomiasis detection and chemotherapy for residents and livestock, snail control, health education, and infectious source control. The mid-term effectiveness of the programme was observed and evaluated longitudinally. RESULTS: From 2004 to 2009, 750 798 schistosomiasis patients and 547 069 persons with the history of infested water contacting were treated. The number of positive cattle treated was 8 462 cattle-times and the number of cattle with history of infested water contact treated was 117 023 cattle-times. The area with snails control by molluscicides was 30 532.0 hm2, and the area with snails control by environmental modification was 13 979.5 hm2. The number of persons who received health education was 31.73 million person-times. The infectious source control measures were carried out in 40% of endemic villages with human infection rate being more than 1%. Up to 2009, the infection rates of population and cattle, and the incidence rate of acute schistosomiasis reduced to 0.51%, 1.25% and 0.30/100 000, respectively. During the period of 2004-2009, the areas with snails fluctuated from 29 065.4 to 29 740.3 hm2. The densities of living snails and infected snails both showed a declining trend in general. During these years, the whole province reached the criteria of infection control, 4 counties reached the criteria of transmission control, and 4 counties reached the criteria of transmission interruption. CONCLUSION: The effect of the comprehensive strategy of schistosomiasis control is remarkable.

[Spatial analysis of distribution of schistosomiasis in Anhui Province].

OBJECTIVE: To study the distribution of schistosomiasis in Anhui Province based on geographic information system (GIS). METHODS: The survey data of disease and Oncomelania snails in Anhui Province in 2006 were collected, GIS databases were set up, and the inverse distance weighted interpolation method (IDW) based on ArcGIS 9.3 was used to analyze the spatial distribution of schistosomiasis across the province. RESULTS: The simulated maps of distribution of human prevalence and positive rate of serological tests were imitated by using IDW. The region with heavier infection rates of schistosomiasis was distributed over the region of the Yangtze River in Anhui Province, and the endemic areas were joined into a patch in the upper and middle reaches and distributed in pieces in the lower reaches. While the endemic areas were compared with the distribution of infected snails, the IDW map of positive rate of serological tests was more exactly than that of the human prevalence. CONCLUSIONS: The IDW method is helpful to show the distribution of schistosomiasis. The positive rate of serological tests is more sensitive to reflect the current endemic situation of schistosomiasis in Anhui Province.

[Effect of project of afforestation for schistosomiasis prevention on snail control in marshland and lake regions].

OBJECTIVE: To evaluate the effect of the project of afforestation for schistosomiasis prevention on Oncomelania hupensis control. METHODS: The situation of afforestation for schistosomiasis prevention in the field and the snail distribution in marshland regions were surveyed with the systematic sampling method in the spring, 2009. The database of snail distribution was established and the status of afforestation was investigated, and the effect of the project on snail control was evaluated. RESULTS: The rates of frames with living snails in the environment with plantations and the environment without a plantation were 14.9% and 19.7%, respectively, and there was a significant difference (Chi2 = 2 267, P < 0.01). The rate of frames with living snails in agroforestry model was lower than that in other models except for fishery-husbandry-forestry model. The average densities of living snails in the environment with plantations and the environment without a plantation were 0.552 snails/0.1 m2 and 0. 989 snails/0.1 m2, respectively. The average densities of living snails in the cultivating group and un-cultivating group were 0.354 snails/0.1 m2 and 0.653 snails/0.1 m2, respectively. The rate of frames with living snails and the average density of living snails were the lowest in the environment of long-term afforestation. CONCLUSIONS: The project of afforestation for schistosomiasis prevention has a good effect on snail control in Anhui Province. Long-term afforestation could stably maintain the effect on snail control.

[Study on the re-emerging situation of schistosomiasis epidemics in areas already under control and interruption].

OBJECTIVE: To study the current situation and the cause of schistosomiasis resurgence in order to provide reference for formulation of control strategy. METHODS: Data in 1999 - 2003 and baseline data in some areas were collected and analyzed retrospectively. RESULTS: Resurgence was seen in 6.15% (16/260) of the areas and one farm where transmission of schistosomiasis had been interrupted and 33.33% (21/64) of the areas already under control. Snails appeared to have been rebounded only in six counties (farm) while in thirty two counties that rebound was seen in both snails and disease prevalence. Tendency of increase in the total numbers of patients, acute patients and cattle with schistosomiasis, areas with snails were seen from 1999 to 2003. CONCLUSIONS: Environmental, ecological, societal factors such as flood, acequia, lack of expenditure and lack of incentives at work etc. contributed to the resurgence of epidemics in those areas that criteria had been reached. Surveillance and supervision on the sources of infection and snail diffusion, especially in the areas where the transmission of schistosomiasis had already been under control.