Kato Satomi, Jenkins Michael, Fogarty Elizabeth, Bowman Dwight
Department of Microbiology and Immunology, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853, USA.
Sci Total Environ. 2004 Apr 5;321(1-3):47-58. doi: 10.1016/j.scitotenv.2003.08.027.
The need exists to understand the environmental parameters that affect inactivation of Cryptosporidium parvum oocysts in soil under field conditions. The inactivation of C. parvum oocysts placed in the natural environment was studied at a dairy farm in western New York State, USA. Seventy sampling points were arranged in a grid with points 150 m apart using the Geographic Information System. The sampling points were distributed among three distinct areas: woodland, corn field and pasture. Purified oocysts were inoculated into chambers filled with soil from each sampling point, and buried in the surface of each respective sampling point. To compare C. parvum oocyst survival with another organism known to survive environmental stresses, Ascaris suum eggs were also placed in soil contained in chambers and buried at the same sampling points as the oocysts. As controls oocysts and eggs in distilled water were also placed at each sampling point. Oocyst and egg viability, soil pH and percent gravimetric water content were measured at all sampling points at 0, 60 and 120 day sampling periods. Soil organic content was determined for each sampling point. At 120 days after placement, mean viability of C. parvum oocysts was 10% although at a few sampling points, 30% of oocysts were still potentially infective; whereas 90% of A. suum eggs were viable at all sampling points. Statistically significant differences were not observed among the three different sampling areas, and no statistically significant predictors were found by regression analysis. Results exemplified the heterogeneity of soil parameters and oocyst viability across a landscape; such results make predictive models for C. parvum inactivation problematical. The long-term survival of C. parvum oocysts in soil under field conditions, as this study demonstrated, emphasizes their potential as a risk to contaminate surface waters.
有必要了解在田间条件下影响土壤中小隐孢子虫卵囊失活的环境参数。在美国纽约州西部的一个奶牛场，研究了置于自然环境中的小隐孢子虫卵囊的失活情况。使用地理信息系统，以相距150米的间隔布置了70个采样点，形成一个网格。采样点分布在三个不同区域：林地、玉米地和牧场。将纯化的卵囊接种到装满每个采样点土壤的小室中，并埋入每个相应采样点的地表。为了将小隐孢子虫卵囊的存活率与另一种已知能在环境压力下存活的生物进行比较，猪蛔虫卵也被置于小室中的土壤中，并埋在与卵囊相同的采样点。作为对照，蒸馏水中的卵囊和虫卵也被放置在每个采样点。在0、60和120天的采样期，在所有采样点测量卵囊和虫卵的活力、土壤pH值和重量含水量百分比。测定每个采样点的土壤有机质含量。放置120天后，小隐孢子虫卵囊的平均活力为10%，尽管在一些采样点，30%的卵囊仍可能具有感染性；而在所有采样点，90%的猪蛔虫卵是有活力的。在三个不同的采样区域之间未观察到统计学上的显著差异，回归分析也未发现统计学上的显著预测因子。结果例证了整个景观中土壤参数和卵囊活力的异质性；这些结果使得小隐孢子虫失活的预测模型存在问题。正如本研究所示，小隐孢子虫卵囊在田间条件下在土壤中的长期存活，强调了它们污染地表水的潜在风险。
