Prohibition of occurrence of viral diseases in the silkworm reared with artificial diet

本课题的一系列研究对家蚕病毒感染的机理提出了新的认识，从化学物质、生理条件、饲料不同营养条件、环境调控等方面进行了研究。(1)建立了幼蚕期和全蚕期人工饲料饲养方法，为家蚕病毒学的基础和应用研究奠定了基础。(2)为研究生物净化室养蚕新体系，研制了一套微生物检测试剂盒。微生物在BCR中的分布模式是清晰的，但一旦在BCR中引入/出现微生物，就很难追踪和清除它们。(3)对感染致核增多症病毒2型的家蚕进行高温处理的研究表明，…积累量受到抑制。治疗后出现了更多的可翻译的mRNAs。由此可见，病毒病的发病条件可以由环境因素控制。(4)建立了几个对细胞质多角体病毒敏感的细胞系。血清素和5-羟色胺被认为是促进中肠运动的因素，从而提高了幼虫对病毒病的抵抗力。(5)取食人工饲料的幼虫对新城疫病毒的感受性比取食桑叶的高10倍。新城疫病毒感染的侏儒细胞在蜕皮时排入肠腔，中肠MIDI处的再生细胞发育成新的上皮细胞进行生理修复，中肠细胞的再生能力主要与家蚕幼虫对新城疫病毒感染的抵抗力有关。(6)已证实盐酸胍(GH)能抑制传染性软骨病病毒(IFV)引起的传染性软骨病的发生。利用无细胞转导系统，明确了GH抑制病毒特异性可翻译的mRNAs和结构多肽在IFV感染的中肠中的积累。因此，提示生长激素对IFV感染的主要作用之一是抑制病毒输入基因组RNA的翻译。(7)一般认为，用人工饲料饲养的幼虫比用桑叶饲养的幼虫更容易感染核型多角体病毒，这取决于肠道汁液中的抗病毒活性较低。研究表明，肠液中的蛋白水解酶活性与其抗病毒活性密切相关，提示不同的饮食性质对病毒通过中肠感染的敏感性不同。较少

The series of studies in this project presented the novel understandings on the mechanis of virus infection of the silkworm in which mod-ulation of the infection by chemicals, physiological conditions, diff-erent neutrient condition of diet, and environmental regulation were conducted. The following conclusions were obtained: (1) The rearing metho using artificial diet during young silkworm stage and whole stage had been established.The both rearing procedures of the silk- worm were very useful for the basic and applied studies of the Bombyx-virology. (2) For the study of new rearing system of the silkworm using a bioclean room (BCR), an assay kit for surveying micobes was developed. The distributing patterns of microbes in BCR were clarfied, but microbes once instroduced/ occuurred in a BCR was considered to be difficult with tracing and removing them. (3) A study on a densonucleosis virus-2 (DNV-2) infected silkworm treated with a high temperature showed that inhibition of an accumul … More ation of translatable mRNAs occurred after that treatment. Therefore, it is demomstrated that a condition of viral desease could be controlled by environmental factors. (4) Several cell lines susceptible for the cyto plasmic polyhedrosis virus were established. Serotnine and 5-hydroxytryptophane were recognized as promoting facters of midgut motility resulting that resistance of larvae against viral disease increased. (5) DNV susceptibility in larvae fed on artificial diets were higher 10 times comparison with that in those fed on mulberry leaves. The DNV infected-midget cells were discharged into the gut lumen at molting and regenerative cell located midi of the midgut developed into new epithelial cells for the physiological repair.The regenerative ability of the midgut cells is mainly concerned with the resistance of the silkworm larvae to the infection of DNV. (6) Guanidine hydrochloride (GH) had been demonstrated to supress the incidence of infectious flacherie caused by infectious flacherie virus (IFV). Using a cell-free trasnaltion system, it was clarified that GH inhibits the accumulation of virus-specific translatable mRNAs and structural polypeptides in the IFV-infected midgut. Therefore, it was suggested that one of the primary function of GH action on the IFV infection is the inhibition of translation of input genomic RNA of the virus. (7) It is generally said that larvae reared on artificial diet were more susceptible to a nuclear-polyhedrosis virus than those reared on mulberry leaves, depending on lower antiviral activity in the gut juice. The study indicated that the protease activity in gut juice was highly concerned with the antiviral activity, suggesting difference susceptibility of virus infection through midgut depending on nature of diets. Less