Sydney School of Veterinary Science, The University of Sydney, Camden 2570, Australia.
Viruses. 2021 May 20;13(5):946. doi: 10.3390/v13050946.
Microvariant genotypes of (OsHV-1) are associated with mass mortality events of Pacific oysters in many countries. The OsHV-1 microvariant (µVar) emerged in France 2008 and caused significant economic losses as it became endemic and displaced the previously dominant OsHV-1 reference genotype. Recently, considerable genotypic variation has been described for OsHV-1 microvariants, however, less is known about variation in viral phenotype. This study used an in vivo laboratory infection model to assess differences in total cumulative mortality, peak viral load, transmissibility, and dose-response for three OsHV-1 isolates obtained between 2011 and 2015 from endemic waterways in Australia. This followed field observations of apparent reductions in the severity of mass mortalities over this time. Significantly higher hazard of death and cumulative mortality were observed for an isolate obtained in 2011 compared to isolates from 2014-2015. In keeping with other studies, the hazard of death was higher in oysters challenged by injection compared to challenge by cohabitation and the mortality was higher when the initial dose was 1 × 10 OsHV-1 DNA copies per oyster injection compared to 1 × 10 DNA copies. There was no difference in the quantity of OsHV-1 DNA at time of death that could be related to isolate or dose, suggesting similar pathogenetic processes in the individual oysters that succumbed to end-stage disease. While the isolates examined in this study were biased towards pathogenic types of OsHV-1, as they were collected during disease outbreaks, the variation in virulence that was observed, when combined with prior data on subclinical infections, suggests that surveillance for low virulence genotypes of OsHV-1 would be rewarding. This may lead to new approaches to disease management which utilize controlled exposure to attenuated strains of OsHV-1.
（OsHV-1）的微变体基因型与许多国家的太平洋牡蛎大规模死亡事件有关。OsHV-1 微变体（µVar）于 2008 年在法国出现，并因成为地方性并取代以前占主导地位的 OsHV-1 参考基因型而造成重大经济损失。最近，已经描述了 OsHV-1 微变体的相当大的基因型变异，但是对病毒表型的变异知之甚少。本研究使用体内实验室感染模型来评估从 2011 年至 2015 年从澳大利亚地方性水道获得的三个 OsHV-1 分离株的总累积死亡率、峰值病毒载量、传染性和剂量反应的差异。这是继该时间段内大规模死亡事件严重程度明显降低的实地观察之后进行的。与 2014 年至 2015 年的分离株相比，2011 年获得的分离株的死亡风险和累积死亡率明显更高。与共培养相比，通过注射挑战的牡蛎的死亡风险更高，并且当初始剂量为每只牡蛎 1×10 OsHV-1 DNA 拷贝时，死亡率比初始剂量为 1×10 DNA 拷贝时更高。在与分离株或剂量相关的时间点，死亡时的 OsHV-1 DNA 数量没有差异，这表明在屈服于终末期疾病的个体牡蛎中存在相似的发病过程。虽然本研究中检查的分离株偏向于 OsHV-1 的致病性类型，因为它们是在疾病爆发期间收集的，但是观察到的毒力变异，结合先前关于亚临床感染的数据，表明对 OsHV-1 的低毒力基因型进行监测将是有益的。这可能导致利用对 OsHV-1 衰减株的受控暴露来进行疾病管理的新方法。
