非典型鸡新城疫的病因研究初报（一）

应用血清学、生物学方法、从我省产蛋量下降、HI抗体在1：128以上的疑似非典型鸡新城疫（CND）病鸡群中分离到1株病毒，经鉴定和致病力测定，明确是1株ND强毒，毒力与F48E9相近，然后采用该株野毒感染不同抗体水平的3批蛋鸡及肉鸡，结果3批蛋鸡均是低抗体滴度组（1：10－1：40）发生了CND症状，感染后6－7天开始产蛋停止，经15－17天后才恢复产蛋，高抗体滴定组（1：80以上）无明显变化，无抗体对照组出现典型鸡新城疫变化，全部死亡；病毒感染后第6、10天监测HI抗体，结果低滴度组第6天达1：80－1：160，第10天达1：160－1：1280。试验结果表明，我们分离到的NDV，既可引起典型的ND，也可引起非典型的ND；高HI抗体蛋鸡产生非典型鸡新城疫的病因之一，是由于存在低抗体鸡群而发生了CND，其高HI抗体有竞争是由于强毒感染后产生的抗体。

A preliminary study reporton the cause of non-typical Newcastle disease

With the application of serology and biology, A strain of Newcastle disease (ND) virus was isolated from a layer chicken flock with non-typical ND symptoms. The ND HI titers of the layer flock were above 1∶128. The consequence of judgment and test of MDT, ICPI and IVPI showed that the NDV isolated was virulent virus. Also its virulence was nearly the same as F48E9. Three layer groups with the different ND antibody levels were infected with a field isolate of NDV experimentally.The consequence showed that three layer groups with low levels of ND HI antibody (1∶10～1∶40) showed CND symptoms and the egg production stopped at 6th (or 7th) day, the egg production restarted at 15th (or 16th or 17th) day.The group with high levels of ND HI antibody (1∶80 or above) didn't show any clinical symptoms.The group of non-vaccinated chicken showed typical ND clinical symptoms,all of them died of infection. HI antibody of the group with low levels of ND HI antibody reached 1∶80～1∶160 at 6th day,reached 1∶160～1∶1280 at 10th day.The consequence showed that the NDV isolated may cause either typical ND or non-typical ND.One cause of the layer chickens with high levels of ND HI antibody being infected was that the group was infected with CND when its ND HI antibody level was low, part of the high level HI antibody was produced with infection of virulent virus.