长江下游江滩地区血吸虫病再流行规律的研究：Ⅰ．钉螺的迁入与消长

目的 阐明长江下游地区钉螺再次迁入无螺江滩后的钉螺消长和分布变迁规律。方法 采用前瞻性观察的方法，每年春季现场调查钉螺分布。结果 每一滩块从局部有螺到全滩有螺平均时间为4．33年，堤外江滩从钉螺迁入到全面有螺的时间需8年，试区从开始有螺到向堤内垦区扩散时间需7年；10年间钉螺面积、钉螺平均密度、有螺框出现率分别增加了74．97倍、90．75倍和106倍；有螺框出现率呈指数曲线y=0.1331e^0.5844x上升；钉螺迁入早期以面积增长为主，在面积扩增到一定程度后，则转变为以螺口增长为主。结论 螺口数量的增加是钉螺扩散的基础，控制钉螺扩散的有效方法是降低螺口的数量。

RE-TRANSMISSION OF SCHISTOSOMASIS JAPONICA IN MARSHLAND OF THE YANGTZE RIVER. I. FLUCTUATION AND DISTRIBUTION OF ONCOMELANIA HUPENSIS

Objectives To understand the fluctuation and distribution pattern of Oncomelania snails after migrated into marshland where no snail infested. Methods The longitudinal survey was performed every spring to understand the snail distribution. Results It took 4.33 years for snails to migrate from one point of marshland to whole marshland. It took about 8 years for snails spread into all of marshlands, and took about 7 years for snail migrated from outside of marshland to inland. During the 10 years, the snail infested areas, snail density, the ratio of snail appearance increased by 74 97, 90 75 and 106 times The ratio of snail appearance increased by index curve in Y=0 1331 e 0 5844x In the early stage, the snail area increased significantly followed by snail density. Conclusion Snail migration is based on the increase of snail population at certain level, so that the efficient measures to control snail is to decline the snail population.