猪乙型脑炎减毒活疫苗毒株的选育研究

以乙脑弱毒SA14－14－2作为母种，采用代地鼠肾细胞和乳鼠皮下传代方法并结合蚀斑纯化技术，选育获得乙脑减毒活疫苗猪用毒株SA14－14－2VS株。该毒株经细胞传到15－18代，脑内接种12－14g小鼠不引起发病和死亡；皮下接种10－12g小鼠，从脑组织中不能分离出病毒；经3－5日龄乳鼠回传一代后，脑内毒力Log LD50仅为1.32-2.10，皮下接种小鼠无致病力。该毒株细胞18代毒，用乳猪传至第五代，从乳猪血液、脑、肝组织中分离的病毒再经细胞传二代，其滴度与原毒液相近，并仍对小鼠脑内感染不致死；8头不公猪经该毒接种后，未发生睾丸炎，睾丸组织中未回收到病毒；经静脉接种的2头怀孕30d的初产母猪，蝇接种后2d和4d血样中检出病毒，但接种21d剖杀时，胎儿均健尖，胎盘、羊水及胎儿脑组织中均未回收到病毒，该毒株能使豚鼠和猪产生较强的免疫应答，对小白鼠攻击的保护力比灭活疫苗主；纯毒及外源因子污染 结果表明，该毒株是纯将的乙脑病毒，符合兽用生物制品种毒标准。

Selection of Attenuated Live-Vaccine Virus Strain of Japanese B. Encephalitis

After passaging the live vaccine strain "SA 14 14 2" virus in BHIC cells or subcutaneous tissue of sucking mice and plaque purification technology, a mutant Japanese Encephalitis virus strain of SA 14 14 2VS used for swine had been obtained. Passaging l 5 l8 generations in cells, the virus couldn't make the mice of 12 14 g sick and die after inoculated into their encephalons. No virus were separated from the mice encephalons after they were inoculated into the subcutaneous tissue of 10 12g mice. Passaging l generation in brains of 3 5 days mice, its virulence was only l .32 2. l Log LD 50 and the strain inoculated subcutaneously had no pathogenicity. The virus of 18 generations in cells was passaged 5 times in new born piglets and the virus separated from blood, encepholon, liver were passaged 2 times in cells, their titres were equal to prime strain and they had no mortality when inoculated in encephalons. The strain was inoculated into 8 male piglets without causing testitis and no virus was isolated again from testicle. The strain was injected into the vein of 2 gilts at 30 days of gestation without examinating virus from blood after 3 or 4 days. The gilts were scalpeled after 21 days, its foetus were all alive, there were no virusseparated again from placenta, amniotic fluid and brain. The strain could induce higher immuning response in guinea pig and swine, the efficiency of protection for mice was higher than the inactive vaccine. According to the results of examination of purification and outer factor contamination, the strain was pure and accord with the standard of virus used as seed of veterinary biology product.