Izumi T, Yagita K, Endo T, Ohyama T
Section of Drinking Water Chemistry, Division of Environmental Hygiene, Hokkaido Institute of Public Health, North 19, West 12, North Ward, Sapporo, 060-0819, Japan.
Arch Environ Contam Toxicol. 2006 Nov;51(4):559-66. doi: 10.1007/s00244-005-0174-9. Epub 2006 Sep 4.
The brackish water benthic shellfish, Corbicula japonica, was experimentally exposed to Cryptosporidium parvum oocysts at 1.51x10(4)oocysts/clam/day for 7 or 14 days. Oocysts were predominantly eliminated through the feces of Corbicula japonica in both cases by microscopic and PCR methods. The fecal excretion rates of oocysts within 4 days after the last exposure to Corbicula japonica were 87.6% for the 7-day exposure group and 86.0% for the 14-day exposure group. The tissue residue level of oocysts in the gastrointestinal tract 3 days after the last exposure was 2.7% of total exposed oocysts and that of 7 days was 1.1% for the 7-day exposure case and 1.6 and 0.5% for the 14-day exposure case, respectively, maintaining infectivity to cultured cells (HCT-8) in vitro. At the same time, field tests of Corbicula japonica for collecting oocysts showed that this clam could certainly collect Cryptosporidium parvum oocysts in the natural river and, furthermore, the gene type of C. parvum could be also identified proving its effectiveness as a biological indicator. The present study showed that the brackish water benthic shellfish Corbicula japonica may be capable of gathering and preserving Cryptosporidium parvum oocysts to a considerable extent under the natural ecological conditions, and further suggests the effectiveness of Corbicula japonica as a practical and general bioindicator for estimates of river water contamination by oocysts of Cryptosporidium parvum.
将微咸水底栖贝类日本蚬置于实验环境中，以1.51×10⁴个卵囊/蛤/天的剂量暴露于微小隐孢子虫卵囊中7天或14天。通过显微镜和聚合酶链式反应（PCR）方法发现，在这两种情况下，卵囊主要通过日本蚬的粪便排出。末次暴露于日本蚬后4天内，7天暴露组的卵囊粪便排泄率为87.6%，14天暴露组为86.0%。末次暴露后3天，胃肠道中卵囊的组织残留水平为总暴露卵囊的2.7%，7天时，7天暴露组为1.1%，14天暴露组分别为1.6%和0.5%，且在体外对培养细胞（HCT-8）保持感染性。同时，对日本蚬采集卵囊的现场测试表明，这种蛤确实可以在天然河流中采集微小隐孢子虫卵囊，此外，还可以鉴定微小隐孢子虫的基因类型，证明其作为生物指示物的有效性。本研究表明，在自然生态条件下，微咸水底栖贝类日本蚬可能在很大程度上能够聚集和留存微小隐孢子虫卵囊，进一步表明日本蚬作为一种实用且通用的生物指示物，对于评估微小隐孢子虫卵囊对河水的污染具有有效性。
