传染性皮下及造血组织坏死病毒(IHHNV)在双壳贝类中的感染情况研究

APPLICATION OF THE INFECTIOUS HYPODERMAL AND HEMATOPOIETIC NECROSIS VIRUS(IHHNV) TO BIVALVE SHELLFISH

采用国际兽医局推荐的传染性皮下及造血组织坏死病毒(infectious hypodermal and hematopoietic necrosis virus,IHHNV)检测方法,首次开展IHHNV在双壳贝类(中国蛤蜊、泥蚶、花蛤、缢蛏、文蛤和白蛤)和螺类软体动物(螺蛳、中华圆田螺)中的感染情况。此外,本研究以泥蚶为研究对象,建立了IHHNV在双壳贝类中的实验室感染模型,研究了人工感染泥蚶后IHHNV在其体内的增殖和致病情况。结果显示:在采集的不同种类贝类样品中均检测到IHHNV,其中在泥蚶中的阳性率最高(50%),在文蛤中的阳性率最低(15%),表明IHHNV在双壳贝类中的分布较为广泛,是IHHNV的重要携带物种。在采集的螺类软体动物中均未检测到IHHNV。系统发育分析表明,来自不同贝类中的IHHNV构成了进化树中不同的分支,其中中国蛤蜊、花蛤、白蛤源的IHHNV属于Ⅱ型感染株,而泥蚶、缢蛏、文蛤源的IHHNV单独成簇,形成了一个全新的分支。实验室感染结果显示,IHHNV对泥蚶没有明显的致病性,但可在其体内增殖,在感染后第5天其体内的病毒载量达到最大(1.8×104copies/g),随着感染时间的增加,其体内病毒含量呈现递减趋势,但在感染后第30天体内仍可检测到病毒的存在。本研究结果对对虾养殖尤其是虾贝混养模式中预防和控制IHHNV的传播具有重要意义。

Detection to the infectious hypodermal and hematopoietic necrosis virus （IHHNV） in bivalve shellfish （Mactra chinensis, Tegillarca granosa, Ruditapes philippinarum, Sinonovacula constricta, Meretrix meretrix and Mactra veneriformis） and snails （Margarya melanioides and Cipangopaludina cahayensis） were first attempted using the method that recommended by the OIE （Office International des Epizooties）. We regarded T. granosa as the research object to establish the IHHNV infection model in bivalve shellfish and studied the replication and pathogenicity of IHHNV in bivalve shellfish after infection. Results demonstrated that IHHNV could be detected in all kinds of the collected shellfish samples with the highest positive rate （50%） in T. granosa and the lowest （15%） in M. meretrix, indicating that IHHNV widely distributed in bivalve shellfish, and bivalve shellfish is an important carrier of IHHNV. However, no IHHNV was detected in the collected snails. Phylogenetic tree analysis indicated that IHHNV from different shellfish species belong to different branches. Among them, IHHNV from M. chinensis, R. philippinarum and M. veneriformis belonged to type II, while IHHNV from T. granosa, S. constricta and M. meretrix formed a completely new branch. The result of infection showed that IHHNV could replicate in T. granosa with no obvious pathogenicity. The maximum viral load in T. granosa （1.8~ l04 copies/g） reached the peak value 5 days post infection. The viral load showed a decreasing trend with the increase of infection time, but the virus could be also detected until 30 days post infection. Therefore, the results of this study are of great significance for the prevention and control of IHHNV transmission in shrimp farming, especially in shrimp and shellfish co-culture farming.