Three Gorges Dam: polynomial regression modeling of water level and the density of schistosome-transmitting snails Oncomelania hupensis

Ya Yang,Wanting Cheng,Yu Yang,Qingqing Dai,Xiang Pan,Lan Zhu,Yibiao Zhou,Jianchuan Gao,Yue Chen,Qingwu Jiang

doi:10.1186/s13071-018-2687-x

Ya Yang, Wanting Cheng + Show 8 more

Open Access

https://doi.org/10.1186/s13071-018-2687-x

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Abstract

BackgroundSchistosomiasis remains a major public health concern in China. Oncomelania hupensis (O. hupensis) is the sole intermediate host of Schistosoma japonicum, and its change in distribution and density influences the endemic S. japonicum. The Three Gorges Dam (TGD) has substantially changed the downstream water levels of the dam. This study investigated the quantitative relationship between flooding duration and the density of the snail population.MethodsTwo bottomlands without any control measures for snails were selected in Yueyang City, Hunan Province. Data for the density of the snail population and water level in both spring and autumn were collected for the period 2009–2015. Polynomial regression analysis was applied to explore the relationship between flooding duration and the density of the snail population.ResultsData showed a convex relationship between spring snail density and flooding duration of the previous year (adjusted R2, aR2 = 0.61). The spring snail density remained low when the flooding duration was fewer than 50 days in the previous year, was the highest when the flooding duration was 123 days, and decreased thereafter. There was a similar convex relationship between autumn snail density and flooding duration of the current year (aR2 = 0.77). The snail density was low when the flooding duration was fewer than 50 days and was the highest when the flooding duration was 139 days.ConclusionsThere was a convex relationship between flooding duration and the spring or autumn snail density. The snail density was the highest when flooding lasted about four to 5 months.

Highlights

Schistosomiasis remains a major public health concern in China
Systematic quadrat sampling was adopted for snail collection in this study [13, 16]. This sampling strategy is designated as the national standard for O. hupensis snail surveys [17] in which setting of the quadrats and the line spacing should be determined according to the size of bottomlands
For the period 2009–2015, the spring snail density ranged between 0.08–19.58 snails/0.11 m2 and the autumn snail density ranged between 0.07–24.50 snails/ 0.11 m2

Summary

Introduction

Schistosomiasis remains a major public health concern in China. Oncomelania hupensis (O. hupensis) is the sole intermediate host of Schistosoma japonicum, and its change in distribution and density influences the endemic S. japonicum. Schistosomiasis is a global public health issue that affects more than 230 million people in approximately 76 countries with a loss of 1.53 million disability-adjusted life years (DALYs) [1,2,3]. It is caused by trematode parasites of the genus Schistosoma, of which Schistosoma japonicum is the only human blood fluke that occurs in southern China. Water level regulation has been used to control the snail population, which led to significant reductions in snail density, snail infection rates and humanwater contact likelihood [5, 10]

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