Surveillance-based evidence:elimination of schistosomiasis as a public health problem in the Peoples’Republic of China

Background:A steady progress on schistosomiasis control in the Peoples’Republic of China(P.R.China)was achieved and broadened into the twelve-year medium and long term national plan(MLNP)which marled the implementation of an integrated control strategy across all endemic areas in P.R.China in 2004.To understand the endemic trends of schistosomiasis to assess the effectiveness of an integrated strategy,we conducted an analysis of schistosomiasis surveillance data spanned from 2005 to 2015.Methods:The schistosomiasis sentinel surveillance data from sentinel sites were collected and analyzed from 2005 to 2015.In these sentinel sites,residents aged 6 years or above were screened annually by indirect hemagglutination assay(IHA),while only antibody positives were followed by stool examination either Kato-katz method(KK)and/or hatching technique(HT).Domestic animals raised in sentinel sites were examined by HT for confirming the infection of schistosomes.Snail investigation was conducted each year through systematic sampling method combined with environmental sampling method.The snails collected from field were tested by microscopic dissection method.The infection rates of schistosomes in residents,domestic animals and snails,as well as the indicators reflecting the snails’distribution were calculated and analyzed.ANOVA analysis was used to examine the changes of the number of eggs per gram feces in population and Chi-square test was used to examine any change in proportions among groups.Results:A total of 148902 residents from sentinel sites attended this study and 631676 blood samples were examined by IHA test during the 11 covered years.The annual average antibody positive rates presented a significant decrease trends,from 17.48%(95%CI:17.20–17.75%)in 2005 to 5.93%(95%CI:5.71–6.15%)(χ2=8890.47,P<0.001)in 2015.During 2005–2015,the average infection rate of schistosomes in residents declined from 2.07%(95%CI:1.96–2.17%)to 0.13%(95%CI:0.09–0.16%),accompanied by significant decrease of infection intensity in population.In 2015,the stool positives were only found in farmers,fishermen and boatmen with infection rate of 0.16%(95%CI:0.11–0.20%),0.17%(95%CI:0–0.50%)respectively.The infection rate of schistosomes in domestic animals dropped from 9.42%(538/5711,95%CI:8.66–10.18%)to 0.08%(2/2360,95%CI:0–0.20%)from 2005 to 2015.Infections were found in eight species of domestic animals at the beginning of surveillance while only two cattle were infected in 2015.Totally 98 ha of new snail habitats were found,while 94.90%(93/98)distributed in lake and marshland regions.The percentage of frames with snails decreased from 16.96%(56884/335391,95%CI:16.83–17.09%)in 2005 to 4.28%(18121/423755,95%CI:4.22–4.34%)in 2014,with a slightly increase in 2015.Meanwhile,the infection rate of schistosomes in snails was decreased from 0.26%(663/256531,95%CI:0.24–0.28%)to zero during 2005–2015.Conclusions:The infection rate of schistosomes declined significantly,providing evidence that the goal of the MLNP was achieved.Elimination of schistosomiasis as a public health problem defined as WHO was also reached in P.R.China nationwide.Surveillance-response system should be improved and strengthened to realize the final goal of schistosomiasis elimination.

Distribution pattern of the snail intermediate host of schistosomiasis japonica in the Poyang Lake region of China

Background:With the closure of the Three Gorges Dam in 2003 the hydrology of Poyang Lake was altered dramatically leading to significant changes in the environment.In order to assess the impact on schistosomiasis this study assessed the spatial and temporal patterns of the snail intermediate host,Oncomelania hupensis in the Poyang Lake tributaries.The results of the study have important implications for future snail control strategies leading to disease elimination.Methods:The marshland area surrounding Poyang Lake was divided randomly into 200×200 m vector grids using ArcGIS software,and the surveyed grids were randomly selected by the software.The snail survey was conducted in each selected grid using a survey frame of 50×50 m with one sideline of each grid serving as the starting line.No less than ten frames were used in each surveyed grid with Global Positioning System(GPS)recordings for each.All snails in each frame were collected to determine infection status by microscopy.Altitude data for all frames were extracted from a lake bottom topographic map in order to analyze the average altitude.All snail survey data were collected and statistically analyzed with SPSS 20.0 software in order to determine the difference of the percentage of frames with living snails and mean density of living snails in different regions of Poyang Lake.The altitude of the snail-infested marshlands and snail dens were subsequently identified.Results:A total of 1159 potential snail sampling grids were surveyed,of which 15231 frames(0.1 m2/frame)were investigated.1241 frames had live Oncomelania snails corresponding to 8.15%of the total number of frames.The mean density of living snails was 0.463/0.1 m2 with a maximum of 57 snails per frame.The percent of frames with snails in the southern sector(8.13%)of Poyang Lake did not differ statistically from the north(8.21%).However,the mean density of live snails in the northern sector(0.164/0.1 m2)of the lake was statistically higher(F=6.727;P=0.010)than the south(0.141/0.1 m2).In the south of the lake,the elevation of snail-inhabited marshland ranged between 11-16 m,and could be further subdivided into two snail-concentrated belts at 12-13 m of elevation and 15-16 m of elevation respectively.In the north of the lake,the elevation of snail-inhabited marshland ranged between 9-16 m with the elevation of 12-14 m being the snail-concentrated zone.Conclusions:The elevation of snail-infested marshlands in the Poyang Lake region ranged from 9 to 16 m.The snail distribution and habitat has moved north of the lake and to a lower altitude due to changes in the water level post dam closure.Based on the current geological features of the snail habitant focused mollusciciding should occur in snail dense northern regions with frequent bovine and human traffic.Targeting these identified'hotspots'of transmission will assist in elimination efforts.

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(χ^(2)=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.

Impact of continuous low water stage on the breeding environment of Oncomelania hupensis: a case study of Poyang Lake area in China

Background Oncomelania hupensis is the only intermediate host of Schistosoma japonicum and plays a decisive role in its transmission.The variation of water level greatly affects the reproduction and growth of snails.Therefore,in this paper,we analyze the variations of water level in the Poyang Lake region from 1993 to 2016 combined with satellite imagery to elucidate the evolution of the snail breeding environment.Methods By employing remote sensing data from 1993 to 2016(April–June and September–November),the vegetation area of Poyang Lake and the vegetation area at different elevations were extracted and calculated.Moreover,the average daily water level data from the four hydrological stations(Hukou station,Xingzi station,Tangyin station and Kangshan station)which represent the typical state of Poyang Lake were collected from 1993 to 2016.The variance of the monthly mean water level,inundation time and the average area were analyzed by variance to find a significance level ofα=0.05.Results According to hydrological data before and after 2003,the average water level after 2003 is significantly lower than that before 2003 in Poyang Lake.After 2003,the time of inundateing the snail breeding period was later in April to June than that before 2003,while the time of wate-falling stage in September to November moved forward after 2003 than before 2003.Of them,the lowest water level affecting the breeding and growing period of O.hupensis in the northern part of Poyang Lake decreased from 11 m to 9 m.After 2003,the expansion of meadow area in the north part of Poyang Lake was mainly concentrated in the elevation of 9–11 m,and the newly increased infested-meadow in the lake area was mainly concentrated in the north part of Poyang Lake.Conclusions By comparing the change of water level characteristics in different parts of the Poyang Lake area as well as changes in meadow area before and after 2003,it is found that the water level changes mainly affect the snail breeding area in the northern part of Poyang Lake.The results are helpful for improving scientific measures for snail control in Jiangxi Province.This approach could also be applicible to Dongting Lake area and other lake areas affected by water level changes and can bring significant guidance for snail control in lake areas.

Schistosomiasis Surveillance--China,2015−2018

Background The prevalence of schistosomiasis in China is at the lowest level in history,and sentinel surveillance sites of schistosomiasis have fully covered all epidemic areas of China.This article has analyzed the surveillance data for the last four years and can help guide the next stage of surveillance work at the national level,including the scope of surveillance,surveillance content,and surveillance methods,etc.Methods Data from the National Schistosomiasis Surveillance System were collected.The infection rate of schistosomiasis among the human population,livestock,snails,and the change of the breeding area of snails in sentinel surveillance sites for four consecutive years were analyzed,and the trends in schistosomiasis prevalence in surveillance sites were determined.Results The prevalence of schistosomiasis in all sentinel surveillance sites of China showed downward trends from 2015 to 2018 with infection rates decreasing in this time period for local human population(0.05%to 0.00%),the floating population(0.020% to 0.003%),and cattle(0.037% to 0.000%).No infected snails were found during the period.From 2015 to 2018,the total area of newly found habitats of snails(Oncomelania hupensis,O.hupensis)were 34,730 m^(2),1,367,694 m^(2),18,944 m^(2),and 50,420 m^(2),and the total area of re-emergent habitats of snails(O.hupensis)were 822,194 m^(2),1,391,779 m^(2),1,516,292 m^(2),and 1,750,558 m^(2),respectively.Conclusions and Implications for Public Health Practice The prevalence of schistosomiasis in human and livestock is going down and is sustained at a very low level,but new and re-emerging habitats of O.hupensis are new challenges regardless of the achievement of schistosomiasis control.Therefore,two actions are necessary to effectively further reduce the transmission risk of schistosomiasis:1)taking effective measures to control the source of infection of schistosomiasis;and 2)reducing the breeding areas of O.hupensis.