钉螺血吸虫感染率与粪便虫卵负荷、钉螺密度相关性的现场实验研究

Field study on the correlation between the snail infection rate and the fecal egg load and snail density

目的研究自然条件下钉螺血吸虫感染率与粪便虫卵负荷、钉螺密度间的相关关系,探讨血吸虫病流行区达传播阻断所需的血吸虫负荷和/或钉螺密度阈值。方法采用两因素三水平的正交设计L9（34）：虫卵负荷设为1 000、5 000和10 000个/m^2,钉螺密度设50、100和200只/m^2,共设置9个实验组。于秋季10月份用含血吸虫虫卵粪便现场感染阴性钉螺,次年春季4月份回收钉螺并压碎镜检钉螺感染情况。结果 9个实验组钉螺感染率在1.09%~25.53%之间;同等粪便虫卵负荷下,钉螺感染率随钉螺密度的降低而增高,1 000只虫卵组有统计学意义（P〈0.01）;经多因素方差分析,钉螺感染率与粪便虫卵负荷、钉螺密度无显著相关性且后二者无交互作用（F=3.930,P〉0.05）。结论当钉螺密度≥5只/0.1 m^2,秋季1 000个及以上血吸虫虫卵可致1 m^2范围内的钉螺感染血吸虫。在钉螺感染环节中粪便虫卵负荷的作用似大于钉螺密度。

Objective To ascertain the correlation between the snail infection rate and the fecal egg load and snail density under natural conditions and explore the thresholds for interruption of Schistosomiasis japonica transmission.Methods Nine experimental groups were established using an orthogonal design（L9（34）） with two factors（fecal egg load snail density） and three levels.The levels of fecal egg load were 1 000,5 000,and 10 000 eggs/m^2,and the levels of snail density were 50,100,and 200 snails/m^2.Snails were attacked by miracidia from egg-positive bovine feces in the autumn,and whether or not they were infected was determined the following spring.Results The rates of snail infection for the nine groups ranged from 1.09% to 25.53%.At the same level of the fecal egg load,the snail infection rate decreased as snail density increased;there was a statistically significant difference for the 1 000-egg group（P〈0.01）.Results of multivariate ANOVA showed that the snail infection rate had no statistically significant correlation with the fecal egg load or snail density.Moreover,there was no interaction between the two factors（F=3.930,P〉0.05）.Conclusion At a snail density beyond 5 snails/0.1 m^2,1 000 or more eggs infected snails within 1 m^2 in the autumn.The fecal egg load may play a greater role in snail infection than snail density.