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

Abstract

BackgroundOwing 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.MethodsMoisture 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.ResultsA 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.ConclusionThe 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.

The influence of natural factors on the spatio-temporal distribution of Oncomelania hupensis

“…A low negative z-score for a feature indicates a statistically significant spatial data outlier. The feature class indicates if the feature has a high value and is surrounded by features with low values (HL) or if the feature has a low value and is surrounded by features with high values (LH) (Wu et al, 2014). This process was implemented in Arcgis 10.1.…”

“…To further explore this influence, annual rainfall, annual average temperature, surface temperature, normalized difference vegetation index, distance from water sources, and historical snail information (the density of living snails the previous year) were subjected to a correlation analysis along with snail density. The main reason for selecting historical factors was to cover the comprehensive influence of other environmental factors (Wu et al, 2014).…”

“…Based on these results, we can infer that the snail has a suitable range of rainfall that is not too high or too low because that would interfere with snail breeding. In this paper, based on the methodology of Wu et al (2014), we further analyzed the range of annual rainfall in the towns with positive regression coefficients and the towns with negative regression coefficients, and the results produced ranges of 802.9 mm-1192.2 mm and 802.9 mm-1482.4 mm, respectively. Thus, in our research area, rainfall was intermediate between promoting and inhibiting the growth of snails.…”

“…Oncomelania hupensis is the only intermediate host of Schistosoma japonicum, and its distribution is consistent with that of S. japonicum. Therefore, investigating the number of Oncomelania hupensis is the key chain in the control of schistosomiasis (Wu et al, 2014). Many studies have shown that the distribution of O. hupensis is closely related to natural factors, especially climate and environmental factors, such as temperature, rainfall, soil, hydrology, and vegetation (Wang and Zhuang, 2015;Zhu et al, 2015;Zhang et al, 2008Zhang et al, , 2013.…”

“…Recognizing these advantages, researchers have applied this method to schistosomiasis studies, but these studies were only preliminary investigations taking place over a relatively short time period and were more concerned with the superiority of the model fit. Besides, there is a lack of thorough studies on the factors influencing snail distribution and a lack of comprehensive comparisons based on multiple sections of time (Wu et al, 2014).…”