Foott J Scott, Stone R, Wiseman E, True K, Nichols K
US Fish and Wildlife Service, California-Nevada Fish Health Center, 24411 Coleman Hatchery Road, Anderson, California 96007, USA.
J Aquat Anim Health. 2007 Jun;19(2):77-83. doi: 10.1577/H06-017.1.
Infectious Ceratomyxa shasta and Parvicapsula minibicornis actinospores were present in Klamath River samples collected in April, May, and June 2005. Juvenile Chinook salmon Oncorhynchus tshawytscha exposed to river water maintained at the ambient Klamath River temperature for 0, 4, 24, 72, and 168 h (7 d) developed asymptomatic infections from both parasites. Elevated water temperature (18 degrees C) in June may have reduced actinospore viability, as both C. shasta and P. minibicornis infection markedly declined in fish exposed for over 72 h. As judged by the prevalence of infection for both parasites, the number of infectious actinospores tended to increase or remain steady through the spring. Ceratomyxa shasta infections were characterized by the presence of a few trophozoites within granulomatous foci in mesentery adipose tissue and were consistently observed outside of the intestine. Similarly, low numbers of P. minibicornis were observed in kidney glomeruli and tubules but were not associated with inflammation. Parvicapsula minibicornis DNA was consistently detected by quantitative real-time polymerase chain reaction in filtered water samples collected each month and from each time posttransfer. These data and the high prevalence of infection observed in the exposed fish indicate that P. minibicornis actinospores were at a relatively high concentration in the river during the spring. In contrast, C. shasta DNA was only detected in half of the water sample sets and its detection did not correspond well to C. shasta infectivity. An approximately threefold increase in river flow from the April to the May water collection was not associated with a decline in either the detection of actinospores (particularly for P. minibicornis) or the prevalence of infection for both parasites. Actinospores of these myxosporean parasites have the potential to infect salmonids for at least 7 d after release from the alternate polychaete host.
2005年4月、5月和6月采集的克拉马斯河样本中存在传染性的沙斯塔尾孢虫（Ceratomyxa shasta）和小角拟胶囊虫（Parvicapsula minibicornis）的放射孢子。将幼年奇努克鲑（Oncorhynchus tshawytscha）暴露于保持克拉马斯河环境温度的河水中0、4、24、72和168小时（7天），两种寄生虫均使鱼发生了无症状感染。6月水温升高（18摄氏度）可能降低了放射孢子的活力，因为暴露超过72小时的鱼中，沙斯塔尾孢虫和小角拟胶囊虫的感染均显著下降。根据两种寄生虫的感染率判断，整个春季传染性放射孢子的数量趋于增加或保持稳定。沙斯塔尾孢虫感染的特征是在肠系膜脂肪组织的肉芽肿病灶内存在少量滋养体，且在肠道外一直能观察到。同样，在肾小体和肾小管中观察到少量小角拟胶囊虫，但未发现炎症。通过定量实时聚合酶链反应，在每月采集的过滤水样以及转移后的每次采样中均持续检测到小角拟胶囊虫的DNA。这些数据以及在暴露鱼中观察到的高感染率表明，春季河流中小角拟胶囊虫放射孢子的浓度相对较高。相比之下，仅在一半的水样中检测到沙斯塔尾孢虫DNA，其检测结果与沙斯塔尾孢虫的感染力并不十分相符。从4月到5月采集水样期间，河流流量增加了约三倍，但这与放射孢子（尤其是小角拟胶囊虫）的检测或两种寄生虫的感染率下降均无关。这些粘孢子虫寄生虫的放射孢子从替代多毛类宿主释放后，至少有7天的时间有可能感染鲑科鱼类。
