Ostreid herpes virus 1 (OsHV-1) has been classified within the Malacoherpesviridae family from the Herpesvirales order. OsHV-1 is the etiological agent of a contagious viral disease of Pacific oysters, C. gigas, affecting also other bivalve species. Mortality rates reported associated with the viral infection vary considerably between sites and countries and depend on the age of affected stocks. A variant called μVar has been reported since 2008 in Europe and other variants in Australia and in New Zealand last decade. These variants are considered as the main causative agents of mass mortality events affecting C. gigas.

Presently there is no established cell line that allows for the detection of infectious OsHV-1. In this context, a technique of propidium monoazide (PMA) PCR was developed in order to quantify “undamaged” capsids. This methodology is of interest to explore the virus infectivity. Being able to quantify viral particles getting an undamaged capsid (not only an amount of viral DNA) in tissue homogenates prepared from infected oysters or in seawater samples can assist in the definition of a Lethal Dose (LD) 50 and gain information in the experiments conducted to reproduce the viral infection.

The main objectives of the present study were (i) the development/optimization of a PMA PCR technique for OsHV-1 detection using the best quantity of PMA and verifying its effectiveness through heat treatment, (ii) the definition of the percentage of undamaged capsids in four different tissue homogenates prepared from infected Pacific oysters and (iii) the approach of a LD50 during experimental viral infection assays on the basis of a number of undamaged capsids. Although the developped PMA PCR technique was unable to determine OsHV-1 infectivity in viral supensions, it could greatly improve interpretation of virus positive results obtained by qPCR. This technique is not intended to replace the quantification of viral DNA by qPCR, but it does make it possible to give a form of biological meaning to the detection of this DNA.

牡蛎疱疹病毒 1 (OsHV-1) 属于疱疹病毒目软疱疹病毒科。OsHV-1 是太平洋牡蛎C. gigas传染性病毒性疾病的病原体，也影响其他双壳类物种。据报道，与病毒感染相关的死亡率在不同地点和国家之间差异很大，并且取决于受影响种群的年龄。自 2008 年以来，欧洲报道了一种名为 μVar 的变种，近十年来澳大利亚和新西兰也报道了其他变种。这些变体被认为是影响巨大念珠菌大规模死亡事件的主要病原体。

目前还没有已建立的细胞系可以检测感染性 OsHV-1。在此背景下，开发了单叠氮化丙啶 (PMA) PCR 技术，以量化“未损坏”的衣壳。这种方法对于探索病毒的感染性很有意义。能够量化受感染牡蛎或海水样本中制备的组织匀浆中获得未受损衣壳（不仅仅是病毒 DNA 量）的病毒颗粒，有助于定义致死剂量 (LD) 50 并在进行的实验中获取信息来重现病毒感染。

本研究的主要目标是 (i) 开发/优化用于 OsHV-1 检测的 PMA PCR 技术，使用最佳量的 PMA 并通过热处理验证其有效性，(ii) 定义未损坏衣壳的百分比在从受感染的太平洋牡蛎制备的四种不同组织匀浆中进行了研究，以及（iii）在实验性病毒感染测定过程中基于许多未受损衣壳的 LD50 方法。尽管开发的PMA PCR技术无法确定病毒悬浮液中的OsHV-1感染性，但它可以极大地改善对qPCR获得的病毒阳性结果的解释。该技术并不是要取代 qPCR 对病毒 DNA 的定量，但它确实可以为这种 DNA 的检测赋予某种形式的生物学意义。