| Objective:To grasp the geographic distribution and epidemic trends of schistosomiasis,this study is trying to establish an ecological niche model analysis method to detect the transmission risk of schistosomiasis in Yunnan Province,and further evaluate the spread of schistosomiasis nationwide,predict the distribution of high-risk areas,and provide a reference for epidemic surveillance and prevention.Methods:The status of endemic counties(cities,districts)at national level and the data of population and cattle inspection were collected from the annual report of national schistosomiasis epidemic situation in 2004-201 7.The dynamic trend of the distribution of endemic areas,the number of patients with schistosomiasis,the serum positive rates of population and the infection rates of bovine were analyzed by descriptive analysis.Based on the data of schistosomiasis control in Yunnan Province from 2004 to 2015,the data of schistosomiasis distribution in administrative villages were obtained,and 13 environmental variables such as climate,geography,social economy were collected.Ten ecological niche models(SRE,GLM,GAM,MARS,GBM,CTA,FDA,ANN,RF,MaxEnt)were established by biomod2 package of R 3.6.1 oftware.Three indexes(AUC value,Kappa statistics and TSS value)were used to evaluate the model accuracy.The importance of environmental variables were analyzed.The optimal model was selected to predict the transmission risk of schistosomiasis in Yunnan Province,and establish the ecological niche modeling analysis method.Based on the annual report of schistosomiasis from 2004 to 2017 and the survey data of schistosomiasis monitoring points from 2005 to 2014,the datasets of schistosomiasis existing points at county-level and village-level were obtained respectively.Based on the ecological niche modeling analysis method,the two sets of data were fitted and compared,the importance of environmental variables was analyzed,and the combination model was constructed through AUC and TSS index screening to assess the transmission risk of schistosomiasis in China.Results:Descriptive analysis of the epidemic situation from 2004 to 2017 showed that the prevention and control work continued to make progress.Among the 12 provinces(municipality and autonomous region)endemic for schistosomiasis in China,Five provinces(municipality and autonomous region),including Shanghai,Zhejiang,Fujian,Guangdong and Guangxi,achieved schistosomiasis elimination in 2016,Sichuan Province achieved transmission interruption in 2017,Yunnan Province achieved transmission control in 2009,Jiangsu Province achieved transmission control in 2010,Hubei Province achieved transmission control in 2014,and three provinces of Anhui,Jiangxi and Hunan achieved transmission control in 2015.The number of schistosomiasis patients in China has decreased year by year,from more than 840,000 in 2004 to less than 40,000 in 2017,with a cumulative decline of more than 95.54%The serum positive rates of human population and the infection rates of bovine in China decreased significantly,reaching the lowest level in history.The results of transmission risk detection of schistosomiasis in Yunnan Province showed that there were statistically significant differences among 10 niche models(AUC,H=73.944,P<0.05,kappa,H=53.034,P<0.05,TSS value,H=53.881,P<0.05),of which RF model has the best performance(AUC=0.976±0.009,Kappa=0.851±0.043,TSS=0.851±0.043),and the top five environmental variables were average annual precipitation(AAP),gross domestic product(GDP),density of population(DP),elevation(EL),Density of bovine population(DBP),accounting for 92.01%.According to the prediction results of niche model based on RF,the transmission risk area accounted for 5.5%of the area of Yunnan Province,mainly distributed in the northwest of Yunnan Province.Among them,the low-risk and medium risk areas accounted for 4.1%and the high-risk areas accounted for 1.4%,which were mainly distributed in the north of Yongsheng County,the north of Heqing County,the East and middle of Eryuan County,the middle and southeast of Dali City,the middle of Weishan Yi Hui Autonomous County,the northwest of Midu,County,and the scattered local areas of Xiangyun County and Yao’an County.In the evaluation of the transmission level of schistosomiasis in China,ten models based on the county-level datasets showed statistically significant differences(AUC,H=63.688,P<0.05,Kappa,H=51.161,P<0.05,TSS,H=51.789,P<0.05).Among them,the RF and GBM models had better performance,and the environmental variables ranked the top:gross domestic product(GDP)and density of population(DP),temperature annual range(BIO7),Annual normalized difference vegetation index(ANDVI),index of Moisture(IM),average annual temperature(AAT),average annual precipitation(AAP).The risk areas predicted by the combined model are widely distributed in the Yangtze River Delta,Pearl River Delta,Poyang Lake,Eastern Hubei,Dongting Lake,central Sichuan and central Yunnan.Most of the risk areas are concentrated in urban areas.The difference between the evaluation indicators of the ten model results based on village-level datasets was statistically significant(AUC,H=69.816,P<0.05,Kappa,H=65.002,P<0.05,TSS,H=66.01 8,P<0.05).GBM,RF,MARS,FDA and ANN were the five models with the best prediction performance;AUC values were greater than 0.9 and TSS values were more than 0.8.The importance of environmental variables was at the forefront:average annual temperature(AAT),elevation(EL),index of Moisture(IM),gross domestic product(GDP),temperature annual range(BIO7),mean diurnal temperature range(BIO2).The risk areas predicted by the combined model are mainly distributed in the middle and lower reaches of the Yangtze River,and some parts of Sichuan Province and Yunnan Province.Finally,a combined ecological niche model based on village-level dataset was selected to evaluate the transmission risk of schistosomiasis in China.The results showed that the distribution area of transmission risk accounted for 10.96%of the whole country,including 4.55%in the low-risk area,2.01%in the medium-risk area,1.91%in the high-risk area and 2.48%in the very high-risk area.High-risk areas and very high-risk areas are mainly distributed in the south of Hubei,the north of Hunan,the middle of Anhui,the south of Jiangsu and the north of Jiangxi.Conclusion:On the whole,the national schistosomiasis transmission has continued to decline and is currently at the lowest level in history.The-ecological niche modeling method can assess the level of schistosomiasis transmission.The modeling results show that the risk of schistosomiasis transmission in Yunnan Province is mainly distributed in some counties(cities)in the northwest region.In the national-scale research,the results of the village-level dataset are significantly better than the results of the county-level dataset.Climate variables play a major role in the modeling process of the disease transmission.The combined model results predict that the risk of schistosomiasis transmission is concentrated in the middle and lower reaches of the Yangtze River. |
