Matsuyama Tomomasa, Miwa Satoshi, Mekata Tohru, Matsuura Yuta, Takano Tomokazu, Nakayasu Chihaya
Fish Pathology Department, Aquaculture Research Department, National Research and Development Agency, Japan Fisheries Research and Education Agency, Minami-Ise, Mie Prefecture, Japan.
PeerJ. 2021 Sep 21;9:e12180. doi: 10.7717/peerj.12180. eCollection 2021.
Mass mortality of 0-year-old pearl oysters, (Gould), and anomalies in adults were observed in Japan's major pearl farming areas in the summer of 2019 and 2020. Although adult oyster mortality was low, both adult and juvenile oysters underwent atrophy of the soft body, detachment of the mantle from nacre (the shiny inner surface of the valves), deposition of brownish material on the nacre, and loss of nacre luster. Infection trials were conducted to verify the involvement of pathogens in this phenomenon. Healthy adult pearl oysters were obtained from areas where this disease had not occurred to use as the recipients. The sources of infection were either affected adult oysters with atrophied soft bodies or batches of juveniles in which mortality had reached conspicuous levels. Transmission of the disease to the healthy oysters were tested either by cohabitation with affected oysters or by injections of the hemolymph of affected animals. The injection infection test examined the effects of filtration and chloroform exposure on the pathogen. Occurrence of the disease was confirmed by the appearance of brown deposits on the nacre and loss of nacre luster. The abnormalities of nacre were clearly reproduced in recipient shells in three out of four cohabitation trials with affected oysters. The disease was also reproduced in six out of six injection trails either with hemolymph filtered through 100 nm filter or with hemolymph treated with chloroform. In a serial passage with hemolymph injections, the disease was successfully transmitted through eight passages. These results suggest that the etiology of the disease is a non-enveloped virus with a diameter ≤100 nm.
2019年夏季和2020年，日本主要珍珠养殖区观察到0龄珍珠贝（ Gould）大量死亡，成年珍珠贝出现异常。尽管成年牡蛎死亡率较低，但成年和幼年牡蛎均出现软体萎缩、外套膜与珍珠层（贝壳内表面有光泽的部分）分离、珍珠层上有褐色物质沉积以及珍珠层失去光泽的现象。进行了感染试验以验证病原体是否与这一现象有关。从未发生该病的地区获取健康成年珍珠贝作为受体。感染源要么是软体萎缩的患病成年牡蛎，要么是死亡率达到显著水平的幼贝批次。通过与患病牡蛎同居或注射患病动物的血淋巴来测试疾病向健康牡蛎的传播情况。注射感染试验研究了过滤和氯仿处理对病原体的影响。通过珍珠层上出现褐色沉积物和珍珠层失去光泽来确认疾病的发生。在与患病牡蛎的四次同居试验中，有三次受体贝壳中明显再现了珍珠层的异常。在用100纳米过滤器过滤的血淋巴或经氯仿处理的血淋巴进行的六次注射试验中，有六次也再现了该病。在血淋巴注射的连续传代试验中，该病成功传播了八代。这些结果表明，该病的病因是一种直径≤100纳米的无包膜病毒。
