| Scallop specimens, including Chlamys farreri and Argopecten irradians, were collected from aquacultured area in Huangdao district of Qingdao, Taiping Bay of Qingdao, Weihai, Laizhou, Rizhao and Changdao. The relaionship between death of cultured scallop and pathogenic infection of virus and rickettsia-like organisms (RLO) was studied by transmission electron microscopy (TEM) technique of ultra-thin sections, negative staining technique and ELISA technique from 2000 to 2002. The results were as following:1. A kind of spherical virus was observed in organs of infected scallop by TEM, which was about 120 to 170nm in diameter and had a bilaminal envelope. The sprikes with approximately 20nm in length could be seen clearly outside the viral membrane. Elliptic RLOs were about 300-500nm in diameter with two-layer membrane and cell wall. There are many ribosomes particles with high electronic density in the central area of RLO.Pathological observation showed that the mantle and hepatopancreas were the main organs of Chlamys farreri infected by virus while the mantle of Argopecten irradians was the only infected organ that could be observed. The virus proliferated in the cytoplasm of infected musculus subcutaneus cells and caused evident ultrastructural changes such as rough endoplasmic reticulum swollen and split, organelle destruction and mitochondrion deformation even forming myeloid body. Karyoplast damage included karyothmma lysis, nuclear pore disappearance, perinuclear space dilatation and nuclear chromatin condensation.2. Epidemiological research indicated that Argopecten irrsdians was infected with virus and RLO from juveniles to adults but infection rate and infection intensity of virus and RLO were at low level and no significant difference. Argopecten irrsdians no mass death showed that there was no direct relationship between virus and RLO and the death of Argopecten irrsdians. Virus and RLO were detected in tissues of Chlamys farreri and infection rate of virus ranged from 80% to 100% during cultured period. The infection intensity of virus varied evidently and the highest infection intensity of virus was found in July and August when acute death of Chlamys farreri occurred. Similar results acquired after Chlamys farreri was injected with virus. The present work demonstrated that infection rates and intensity of RLO were not significantly different for cultured and artificial infected Chlamys farreri. The observation in scallop specimens confirmedthat the direct pathogen of explosive epidemic disease of Chlamys farreri was possibly a spherical virus. It seemed that there was no direct relationship between RLO and the death of Chlamys farreri. The environmental factors such as temperature, salinity, pH and DO were investigated in 2001. Results indicated that the high temperature above 24 癈 was the important incitant.3. The acute virus necrobiotic disease virusC AVND virus)was isolated from diseased scallop Chlamys farreri collected in the Taiping Bay of Qingdao. Using purified virus as antigens, the polyclonal antibody with high titer was prepared in rabbits. The polyclonal antibody as the first antibody, IgG-HRP as the second antibody, indirect ELISA technique was set up through selecting the best interactional conditions among the first antibody, the second antibody and antigen. Sensitivity and specificity were ideal which the minimum quantity of virus to be detected was 30ng. The ELISA technique was used to detect the AVND virus within 5 to 7 hours.Then scallop Chlamys farreri specimens were collected from Qingdao, Weihai, Laizhou, Rizhao and Changdao of Shandong province from 2000 to 2002 during various periods. The infection conditions of acute virus necrobiotic disease virus were detected by indirect ELISA technique. The results showed that the positive rates of AVND-virus infection ranged from 75% to 95% during epizootic period in July and August and was low in the rest growth period. July and August was bad attack time of the virus infection. The present work demonstrated that a high... |
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