Purcell M K, Garver K A, Conway C, Elliott D G, Kurath G
Western Fisheries Research Center, U.S. Geological Survey, Seattle, WA 98115, USA.
J Fish Dis. 2009 Jul;32(7):619-31. doi: 10.1111/j.1365-2761.2009.01045.x. Epub 2009 May 22.
Characterization of infectious haematopoietic necrosis virus (IHNV) field isolates from North America has established three main genogroups (U, M and L) that differ in host-specific virulence. In sockeye salmon, Oncorhynchus nerka, the U genogroup is highly virulent, whereas the M genogroup is nearly non-pathogenic. In this study, we sought to characterize the virus-host dynamics that contribute to genogroup-specific virulence in a captive stock of sockeye salmon from Redfish Lake in Idaho. Juvenile sockeye salmon were challenged by immersion and injection with either a representative U or M viral strain and sampled periodically until 14 days post-infection (p.i.). Fish challenged with each strain had positive viral titre by day 3, regardless of challenge route, but the fish exposed to the M genogroup virus had significantly lower virus titres than fish exposed to the U genogroup virus. Gene expression analysis by quantitative reverse transcriptase PCR was used to simultaneously assess viral load and host interferon (IFN) response in the anterior kidney. Viral load was significantly higher in the U-challenged fish relative to M-challenged fish. Both viruses induced expression of the IFN-stimulated genes (ISGs), but expression was usually significantly lower in the M-challenged group, particularly at later time points (7 and 14 days p.i.). However, ISG expression was comparable with 3 days post-immersion challenge despite a significant difference in viral load. Our data indicated that the M genogroup virus entered the host, replicated and spread in the sockeye salmon tissues, but to a lesser extent than the U genogroup. Both virus types induced a host IFN response, but the high virulence strain (U) continued to replicate in the presence of this response, whereas the low virulence strain (M) was cleared below detectable levels. We hypothesize that high virulence is associated with early in vivo replication allowing the virus to achieve a threshold level, which the host innate immune system cannot control.
对来自北美的传染性造血坏死病毒（IHNV）野外分离株的特征分析确定了三个主要基因群（U、M和L），它们在宿主特异性毒力方面存在差异。在红大马哈鱼（Oncorhynchus nerka）中，U基因群具有高毒力，而M基因群几乎无致病性。在本研究中，我们试图描述在爱达荷州红鱼湖圈养的红大马哈鱼种群中，导致基因群特异性毒力的病毒-宿主动态变化。将幼年红大马哈鱼通过浸泡和注射的方式分别用代表性的U或M病毒株进行攻毒，并定期取样直至感染后14天（p.i.）。无论攻毒途径如何，用每种病毒株攻毒的鱼在第3天时病毒滴度均为阳性，但暴露于M基因群病毒的鱼的病毒滴度显著低于暴露于U基因群病毒的鱼。通过定量逆转录PCR进行基因表达分析，以同时评估前肾中的病毒载量和宿主干扰素（IFN）反应。相对于M攻毒组，U攻毒组的鱼的病毒载量显著更高。两种病毒均诱导了干扰素刺激基因（ISGs）的表达，但在M攻毒组中表达通常显著较低，尤其是在后期时间点（感染后7天和14天）。然而，尽管病毒载量存在显著差异，但浸泡攻毒后3天时ISG表达相当。我们的数据表明，M基因群病毒进入宿主后，在红大马哈鱼组织中复制并传播，但程度低于U基因群。两种病毒类型均诱导了宿主IFN反应，但高毒力毒株（U）在这种反应存在的情况下继续复制，而低毒力毒株（M）被清除至检测不到的水平。我们推测，高毒力与早期体内复制相关，使病毒达到宿主先天免疫系统无法控制的阈值水平。
