Hurst Charlene N, Wong Peter, Hallett Sascha L, Ray R Adam, Bartholomew Jerri L
Department of Microbiology, Oregon State University, Corvallis, Oregon 97331.
J Parasitol. 2014 Dec;100(6):773-7. doi: 10.1645/13-482.1.
Ceratonova shasta is a myxozoan parasite of salmon and trout transmitted by waterborne actinospores. Based on DNA sequence data and host specificity, 4 distinct parasite genotypes are recognized. Genotypes I and II are common in the lower reaches of the Klamath River, Oregon-California, but only infection by genotype I causes mortality in Chinook salmon. We conducted sentinel fish exposures and determined genotype composition in river water during exposure, and in fish gills, intestine, and tank water post-exposure to determine whether: (1) transmission of parasites having different genotypes is host-specific and (2) all transmitted genotypes persist in the host through to release as waterborne stages. Initial parasite transmission to the fish host appears indiscriminant, since we detected both genotypes I and II in 83.6% of the fish gills sampled. However, only genotype I was detected in fish that succumbed to infection, while both genotypes persisted in fish that survived. Persistence was likely dependent on exposure dose, initial infection type (mixed or single) and infection outcome (mortality or survival). The transmission of both genotypes to a majority of Chinook salmon and the persistence of multiple genotypes raises questions about how infection with mixed genotypes could result in within-host interactions that affect disease severity.
沙斯塔角孢子虫是一种通过水生放射孢子传播的鲑鱼和鳟鱼的粘孢子虫寄生虫。根据DNA序列数据和宿主特异性，可识别出4种不同的寄生虫基因型。基因型I和II在俄勒冈州-加利福尼亚州克拉马斯河下游很常见，但只有基因型I的感染会导致奇努克鲑鱼死亡。我们进行了哨兵鱼暴露实验，并确定了暴露期间河水中以及暴露后鱼鳃、肠道和养殖池水中的基因型组成，以确定：（1）具有不同基因型的寄生虫的传播是否具有宿主特异性，以及（2）所有传播的基因型是否在宿主体内持续存在直至以水生阶段释放。最初寄生虫向鱼类宿主的传播似乎是无差别的，因为我们在83.6%的采样鱼鳃中检测到了基因型I和II。然而，在死于感染的鱼中仅检测到基因型I，而两种基因型在存活的鱼中都持续存在。持续性可能取决于暴露剂量、初始感染类型（混合或单一）和感染结果（死亡或存活）。两种基因型向大多数奇努克鲑鱼的传播以及多种基因型的持续性，引发了关于混合基因型感染如何导致影响疾病严重程度的宿主体内相互作用的问题。
