House M L, Bartholomew J L, Winton J R, Fryer J L
Center for Salmon Disease Research, Oregon State University, Corvallis 97331-3804, USA.
Dis Aquat Organ. 1999 Jan 29;35(2):107-13. doi: 10.3354/dao035107.
Piscirickettsia salmonis was first recognized as the cause of mortality among pen-reared coho salmon Oncorhynchus kisutch in Chile. Since the initial isolation of this intracellular Gram-negative bacterium in 1989, similar organisms have been described from several areas of the world, but the associated outbreaks were not reported to be as serious as those that occurred in Chile. To determine if this was due to differences in virulence among isolates of P. salmonis, we conducted an experiment comparing isolates from Chile, British Columbia, Canada, and Norway (LF-89, ATL-4-91 and NOR-92, respectively). For each of the isolates, 3 replicates of 30 coho salmon were injected intraperitoneally with each of 3 concentrations of the bacterium. Negative control fish were injected with MEM-10. Mortalities were collected daily for 41 d post-injection. Piscirickettsiosis was observed in fish injected with each of the 3 isolates, and for each isolate, cumulative mortality was directly related to the concentration of bacterial cells administered. The LF-89 isolate was the most virulent, with losses reaching 97% in the 3 replicates injected with 10(5.0) TCID50, 91% in the replicates injected with 10(4.0) TCID50, and 57% in the fish injected with 10(3.0) TCID50. The ATL-4-91 isolate caused losses of 92% in the 3 replicates injected with 10(5.0) TCID50, 76% in the fish injected with 10(4.0) TCID50, and 32% in those injected with 10(3.0) TCID50. The NOR-92 isolate was the least virulent, causing 41% mortality in the replicates injected with 10(4.6) TCID50. At 41 d post-injection, 6% of the fish injected with 10(3.6) TCID50 NOR-92 had died. Mortality was only 2% in the fish injected with 10(2.6) TCID50 NOR-92, which was the same as the negative control group. Because the group injected with the highest concentration (10(4.6) TCID50) of NOR-92 was still experiencing mortality at 41 d, it was held for an additional 46 d. At 87 d post-injection, the cumulative mortality in this group had reached 70%. These differences in virulence among the isolates were statistically significant (p < 0.0001), and are important for the management of affected stocks of fish.
鲑鱼立克次氏体最初被认为是智利网箱养殖银大麻哈鱼（Oncorhynchus kisutch）死亡的原因。自1989年首次分离出这种细胞内革兰氏阴性细菌以来，世界上几个地区都描述了类似的生物体，但据报道相关疫情没有智利发生的那么严重。为了确定这是否是由于鲑鱼立克次氏体分离株之间毒力的差异，我们进行了一项实验，比较来自智利、加拿大不列颠哥伦比亚省和挪威的分离株（分别为LF-89、ATL-4-91和NOR-92）。对于每种分离株，将30尾银大麻哈鱼分成3组重复实验，每组分别腹腔注射3种浓度的细菌。阴性对照鱼注射MEM-10。注射后41天每天收集死亡情况。在注射了3种分离株的鱼中都观察到了鲑鱼立克次氏体病，对于每种分离株，累积死亡率与接种的细菌细胞浓度直接相关。LF-89分离株毒性最强，在注射10(5.0) TCID50的3组重复实验中死亡率达到97%，在注射10(4.0) TCID50的重复实验中死亡率为91%，在注射10(3.0) TCID50的鱼中死亡率为57%。ATL-4-91分离株在注射10(5.0) TCID50的3组重复实验中导致92%的死亡，在注射10(4.0) TCID50的鱼中死亡率为76%，在注射10(3.0) TCID50的鱼中死亡率为32%。NOR-92分离株毒性最弱，在注射10(4.6) TCID50的重复实验中导致41%的死亡率。注射后41天，注射10(3.6) TCID50 NOR-92的鱼中有6%死亡。注射10(2.6) TCID50 NOR-92的鱼死亡率仅为2%，与阴性对照组相同。由于注射最高浓度（10(4.6) TCID50）NOR-92的组在41天时仍有死亡，因此将其再饲养46天。注射后87天，该组的累积死亡率达到70%。分离株之间的这些毒力差异具有统计学意义（p < 0.0001），对受影响鱼类种群的管理很重要。
