Ifremer, RBE-ASIM, Station de La Tremblade, La Tremblade, France.
Réseau d'EpidémioSurveillance en Pathologie Equine, Saint-Contest, France.
Transbound Emerg Dis. 2022 Sep;69(5):e2041-e2058. doi: 10.1111/tbed.14541. Epub 2022 Apr 12.
The Pacific cupped oyster Crassostrea gigas is one of the most 'globalized' marine invertebrates and its production is predominant in many parts of the world including Europe. However, it is threatened by mortality events associated with pathogenic microorganisms such as the virus OsHV-1 and the bacteria Vibrio aestuarianus. C. gigas is also a host for protozoan parasites including haplosporidians. In contrast with Haplosporidium nelsoni previously detected in Europe, H. costale was considered exotic although its presence in French oysters was suggested in the 1980s based on ultrastructural examination. Here, a combination of light and transmission electron microscopy, PCR and sequencing allowed characterizing the presence of the parasite in the context of low mortality events which occurred in 2019 in France. Histological observation revealed the presence of uninucleated, plasmodial and spore stages within the connective tissues of some oysters. Ultrastructural features were similar to H. costale ones in particular the presence of axe-shaped haplosporosomes in spore cytoplasms. Three fragments of the genome including partial small subunit rRNA gene, the ITS-1, 5.8S and ITS-2 array and part of the actin gene were successfully sequenced and grouped with H. costale homologous sequences. This is the first time that the presence of H. costale was confirmed in C. gigas in France. Furthermore, a TaqMan real-time PCR assay was developed and validated [DSe = 92.6% (78.2-99.8) and DSp = 95.5% (92.3-98.6)] to enable the rapid and specific detection of the parasite. The application of the PCR assay on archived samples revealed that the parasite has been present in French oyster populations at least since 2008. Considering the little information available on this parasite, the newly developed TaqMan assay will be very helpful to investigate the temporal and geographic distribution and the life cycle of the parasite in France and more generally in C. gigas geographic range.
太平洋牡蛎 Crassostrea gigas 是最具“全球化”的海洋无脊椎动物之一，其产量在世界许多地区都占主导地位，包括欧洲。然而，它受到与致病性微生物（如病毒 OsHV-1 和细菌 Vibrio aestuarianus）相关的死亡率事件的威胁。C. gigas 也是原生动物寄生虫的宿主，包括哈氏胞子虫。与以前在欧洲检测到的 Haplosporidium nelsoni 不同，Haplosporidium costale 被认为是外来物种，尽管 20 世纪 80 年代基于超微结构检查就曾提示其存在于法国牡蛎中。在这里，结合光镜和透射电子显微镜、PCR 和测序，能够在 2019 年法国发生的低死亡率事件背景下对寄生虫的存在进行特征描述。组织学观察显示，在一些牡蛎的结缔组织中存在单核、质体和孢子阶段。超微结构特征与 H. costale 相似，特别是孢子细胞质中存在斧形哈氏胞子体。成功测序了包括部分小亚基 rRNA 基因、ITS-1、5.8S 和 ITS-2 区以及部分肌动蛋白基因的三个基因组片段，并与 H. costale 同源序列进行了分组。这是首次在法国的 C. gigas 中确认存在 H. costale。此外，还开发并验证了 TaqMan 实时 PCR 检测方法 [DSe = 92.6%（78.2-99.8）和 DSp = 95.5%（92.3-98.6）]，以实现寄生虫的快速和特异性检测。将 PCR 检测方法应用于存档样本显示，该寄生虫至少自 2008 年以来就存在于法国牡蛎种群中。考虑到关于该寄生虫的信息很少，新开发的 TaqMan 检测方法将非常有助于调查法国和更广泛的 C. gigas 地理范围内寄生虫的时间和地理分布以及生命周期。
