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[Impact of the changing water level on the variance of Oncomelania hupensis populations in Lake Area with general additive model]

ArticleinZhonghua liu xing bing xue za zhi = Zhonghua liuxingbingxue zazhi 31(10):1148-54 · October 2010with6 Reads
Source: PubMed
Abstract
To explore the impact and regularity of snail population after changing of water level and to develop effective control and prediction programs. A typical snail habitat closed to Changjiang county in Yueyang city, Hunan province was selected as the survey field. Data on water level and the changing trend of snail population during 2001 - 2009 including the average water level, maximum and minimum water levels, snail and infected snail densities, proportion of sampling frames with living and infected snails etc. were collected. The distribution of water level and snail indexes were described and a general additive model (GAM) for the relationships between these indexes were also fitted. Impacts of the average water level and the watered-out days in current year in the surveyed field on the snail density were statistically significant (P<0.01), showing a quadratic curve association. The snail density remained at the lowest level when the average water level was at 25.0 m and the surveyed field watered-out days was 120. The average water level in current year and the field watered-out days in the past year showed statistically significant impacts on the infected snail density (P<0.001), the proportion of sampling frames with infected snails (P<0.05) and living snails (P value neared 0.05), presented a quadratic curve, a cubic curve or even a more complicated piecewise curve association. Both the infected snail density and the proportion of sampling frames with infected snails remained at the lowest level when the average water level was at 25.0 m and the watered-out days in the past year was 110, while the proportion of sampling frames with living snails kept the lowest level when the average water level was at 25.0 m and the watered-out days in the past year was 160. The water level and the field watered-out days affected the development of snail population directly. The changing water level had an impact on snail population change, which mainly presented as nonlinear smooth function relation. Impact of the field watered out days on the infected snail density and the proportion of sampling frames with living snails and infected snails showed a hysteresis effect. The snail density was predicted to be retaining a high level when the water level was 24.0 m and the field watered-out days was 3 months. It had obvious advantages to fit the relationship of the changing water level and the snail indexes with a GAM which could get closer to the reality as well as easier to find and explain the potential associations and regulations.
    • "A study revealed that snail density and the percent of frames with snail was highest when the groundwater level was around 32 cm, and soil moisture content of 28e38% was optimal for snail breeding (Zhang et al., 1999). Water-level fluctuation can affect the macro-and micro-environment of snail habitats as well as snail's life activity and distribution status, which in turn, affect schistosomiasis transmission (Li et al., 2010a; Ma et al., 2011). Snails are few in low-elevation marshlands that are submerged over 8 months, or high-elevation marshlands that are submerged less than 3 months. "
    [Show abstract] [Hide abstract] ABSTRACT: Schistosomiasis caused by Schistosoma japonicum is a severe parasitic disease in China and imposed considerable burden on human and domestic animal health and socioeconomic development. The significant achievement in schistosomiasis control has been made in last 60 years. Oncomelania hupensis as the only intermediate host of S. japonicum plays a key role in disease transmission. The habitat complexity of the snails challenges to effective control. In this review we share the experiences in control and research of O. hupensis.
    Chapter · Apr 2016
    Z.J. LiZ.J. LiJ. GeJ. GeJ.R. DaiJ.R. Dai+4 more authors ...S. LvS. Lv
    • "Rainfall pattern in the area is seasonal, with the heaviest rain falling from April to June and the lightest rain dropping from December to February. This kind of environment is quite suitable for snails to live and reproduce, meaning that Dongting Lake Region has provided optimal circumstances for S. japonica for a long time3738394041. "
    [Show abstract] [Hide abstract] ABSTRACT: 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.
    Full-text · Article · May 2014
    • "Rainfall pattern in the area is seasonal, with the heaviest rain falling from April to June and the lightest rain dropping from December to February. This kind of environment is quite suitable for snails to live and reproduce, meaning that Dongting Lake Region has provided optimal circumstances for S. japonica for a long time [37][38][39][40][41]. "
    [Show abstract] [Hide abstract] ABSTRACT: The epidemiology of schistosomiasis japonicum over small areas remains poorly understood, and this is particularly true in China. We aimed to identify high-risk areas for schistosomiasis and associated risk factors in the Poyang Lake region, China. A cross-sectional study was conducted and 60 of 920 persons (6.5%) were found to be infected with Schistosoma japonicum. Locations of households and snail habitats were determined using a hand-held global positioning system. We mapped the data in a geographical information system and used spatial scan statistics to explore clustering of infection, logistic regression and Bayesian geostatistical models to identify risk factors for each individual's infection status and multinomial logistic regression to identify risk factors for living in a cluster area. The risk of schistosomiasis was spatially clustered and higher in fishermen and males, not in persons who lived in close proximity to snail habitats and infected water sources. This study has demonstrated significant spatial variation in the prevalence of schistosomiasis at a small spatial scale. The results suggest that demographic factors (gender, occupation) rather than the distance to infected water are driving human transmission at small-scale spatial levels. Such information can be used to plan locally targeted interventions based on anthelminthic drug administration, snail control and sanitation improvement.
    Full-text · Article · Jun 2010