[Analysis of relationship between natural death of Oncomelania hupensis snails and water level in Eastern Dongting Lake district].

OBJECTIVE: To study the reasons of natural death of Oncomelania hupensis snails by comparing the differences of the indicator days covered with water (DCW) in snail marshland and non-snail marshland around the build of Three Gorges Dam in Eastern Dongting Lake areas. METHODS: Two marshlands were selected, one was a non-snail marshland (Qianliang Lake) and another was a snail marshland (Junshan Park). The measuring points were set through the mechanical sampling. The snails and elevation of the points were surveyed, and the data of the water levels from the hydrological station were collected, and then DCWs were calculated. RESULTS: From 1995 to 2013, DCWs of the marshland of natural death of snails were all more than that of the snail marshland (P < 0.01). In Qianliang Lake marshland, the difference between DCW before natural death and DCW from natural death until the dam was not significant (P = 0.23), while DCWs of the two stages both were more than that after the dam (P1 = 0.045, P2 = 0.002). Before the build of the dam, DCW of the Qianliang Lake marshland of natural death of snails was more than that after the build of the dam (P = 0.013), and there was the same situation in Junshan Park marshland (P = 0.005). The relationship between snail density and DCW was not significant in Junshan Park marshland (r(s) = 0.008, P = 0.914), and the reference range of DCW of all the measuring points was 76-251 days. CONCLUSION: In the eastern Dongting Lake district, the build of Three Gorges Dam and DCW may be not the direct factors affecting the natural death of snails and the latter may change the distribution of snails.

[Contrastive analysis of environmental factors between Oncomelania hupensis snail marshland and snail natural death marshland in eastern Dongting Lake schistosomiasis endemic areas].

OBJECTIVE: To study the reasons of natural death of Oncomelania hupensis snails in marshland by comparing the differences of environmental factors between snail marshland and non-snail marshland in East Dongting Lake schistosomiasis endemic areas. METHODS: Two adjoining marshlands were selected, one was a snail marshland and another was a non-snail marshland. The measuring points were set by grid of "20 m x 20 m". The soil moisture, elevation, soil pH and temperature of the points were measured, and the snails of the points were surveyed. RESULTS: The elevation, soil pH and temperature of the snail natural death marshland were all lower than those of the snail marshland (P < 0.01). The soil moisture, elevation, soil pH and temperature of different snail densities in the snail marshland were different (P < 0.05). The soil moisture of the non-snail group was higher than that of other four groups (P < 0.01) and the soil moisture of the group with 0-11 snails per frame was lower than that of other four groups (P < 0.01). The elevation of the group with 0-11 snails per frame was lower than that of the group with 24-39 snails per frame and the group with more than 39 snails per frame (P < 0.05). The soil pH of the group without snails was higher than that of other four groups (P < 0.01) and the soil temperature of the group with 0-11 snails per frame was lower than that of the group with 24-39 snails per frame. The differences of soil moisture and elevation of different death snail densities were not significant, while the differences of soil pH and temperature were significant. The soil pH of the non-snail died group was higher than that of the 2-died, 3-died and more than 3-died groups (P < 0.05). The soil temperature of the non-snail died group was higher than that of other four groups (P < 0.05). CONCLUSION: The elevation, soil pH and soil temperature within the range of the research may be the factors affecting the snail natural death and the soil moisture, elevation, soil pH and soil temperature may be the factors affecting the distribution of snails.

Identification of optimum scopes of environmental factors for snails using spatial analysis techniques in Dongting Lake Region, China.

BACKGROUND: Owing to the harmfulness and seriousness of Schistosomiasis japonica in China, the control and prevention of S. japonica transmission are imperative. As the unique intermediate host of this disease, Oncomelania hupensis plays an important role in the transmission. It has been reported that the snail population in Qiangliang Lake district, Dongting Lake Region has been naturally declining and is slowly becoming extinct. Considering the changes of environmental factors that may cause this phenomenon, we try to explore the relationship between circumstance elements and snails, and then search for the possible optimum scopes of environmental factors for snails. METHODS: Moisture content of soil, pH, temperature of soil and elevation were collected by corresponding apparatus in the study sites. The LISA statistic and GWR model were used to analyze the association between factors and mean snail density, and the values in high-high clustered areas and low-low clustered areas were extracted to find out the possible optimum ranges of these elements for snails. RESULTS: A total of 8,589 snail specimens were collected from 397 sampling sites in the study field. Besides the mean snail density, three environmental factors including water content, pH and temperature had high spatial autocorrelation. The spatial clustering suggested that the possible optimum scopes of moisture content, pH, temperature of the soil and elevation were 58.70 to 68.93%, 6.80 to 7.80, 22.73 to 24.23°C and 23.50 to 25.97 m, respectively. Moreover, the GWR model showed that the possible optimum ranges of these four factors were 36.58 to 61.08%, 6.541 to 6.89, 24.30 to 25.70°C and 23.50 to 29.44 m, respectively. CONCLUSION: The results indicated the association between snails and environmental factors was not linear but U-shaped. Considering the results of two analysis methods, the possible optimum scopes of moisture content, pH, temperature of the soil and elevation were 58.70% to 68.93%, 6.6 to 7.0, 22.73°C to 24.23°C, and 23.5 m to 26.0 m, respectively. The findings in this research will help in making an effective strategy to control snails and provide a method to analyze other factors.

[Distribution of univalvia molluscs in area with natural decline of Oncomelania hupensis snails in Eastern Dongting Lake area].

OBJECTIVE: To understand the distribution of univalvia molluscs in Eastern Dongting lake area where the Oncomelania hupensis is extinct, so as to explore the causes of extinction and to provide the evidence for formulating schistosomiasis control strategy. METHODS: The univalvia molluscs of the Qianliang Lake district, Jianxin District and Junshan Park were investigated in August of 2013. All the collected snails were classified and identified. The data were analyzed by using the method of Shapiro-Wilk normality test and non-parametric test. The ecological biodiversity differences from each district were compared by the biodiversity indexes. RESULTS: The univalvia molluscs collected were from 6 species in 3 families in Gastropoda class, namely Oncomelania hupensis Gredler in Pomatiopsidae family, Parafossarulus striatulus, Alocinma longicornis, Parafossarulus sineasis, Bithynia fuchsisana in Bithyniidae family, and one genus provisioy nally named Radix in Lymaneidae family. In Junshan Park, a total of 4553 snails were collected, among which 1264 were Oncomelania snails. In Jianxin District, 336 univalvia molluscs were collected, and no Oncomelania snails were found. In Qianliang Lake district, there were only 7 Alocinma longicornis snails, 2 Parafossarulus sinensis snails and 1 Parafossarulus striatulus snail collected. There were significant differences among the distributions of the samples from the three districts (chi2 = 166.225, P < 0.01) .The Simpson's diversity indexes in Qianliang Lake area, Jianxin Dis- trict and Junshan Park were 0.4028, 0.7186 and 0.6788, respectively, and the Shannon-Wiener indexes of the 3 areas were 0.7215, 1.4313 and 1.1999, respectively. CONCLUSIONS: With the extinction of Oncomelania snails, the species and quantities of other snails become rare in Qianliang Lake area. Whether their causes are relevant is worth further studying.

[Natural growth and decline of Oncomelania hupensis snails in marshland of Qianliang Lake District in Eastern Dongting Lake area, China].

OBJECTIVE: To understand the change trend of Oncomelania hupensis snails in the bottomland areas of Qian Liang Lake district in Eastern Dongting Lake area so as to provide the evidence for formulating a schistosomiasis control strategy. METHODS: The monitoring data of snails of Qianliang Lake district from 1988 to 2011 were collected retrospectively and analyzed by using the method of the trend Chi-square test. The correlations among the snail density indicators were analyzed. RESULTS: 1988 to 2011, the area of snails surveyed did not change and was 433.2 hm(2). The monitoring data showed that the change trend of the density of living snails and the schistosome infection rates of snails were not obvious (P > 0.05), but the mortality of snails showed a falling trend (P < 0.05); There were positive correlations between the average density of infected snails and the mortality of snails (r = 0.640, P < 0.05) , the infection rate of snails (r = 0.639, P < 0.05) , and the average density of living snails (r = 0.646, P < 0.05) , respectively. There was no correlation among other snail indicators. In 1999, only 7 snails were found, of them, only one snail was alive. The alive snails were not found after 2000. CONCLUSION: In the bottomland areas of Qianliang Lake district, the change trend of the density of alive snails were not obvious from 1988 to 1998, but the number of snails underwent a sharp drop in 1999 and snails have been not found till now.