免疫雏鹅发生小鹅瘟的原因分析

Causal Analysis on Gosling Plague Occurred in Immunized Flocks

2018年6月,安徽某鹅场接种过小鹅瘟蛋黄抗体的2批雏鹅发生小鹅瘟,再次用小鹅瘟蛋黄抗体产品进行紧急接种,有一定的控制效果,但仍有雏鹅死亡。为分析其原因,采集了8只9-12日龄病死鹅的肝脏和脾脏,用PCR扩增检测水禽细小病毒的VP3基因,选8份阳性样品测定了鹅细小病毒(GPV)VP1部分序列并进行了序列分析。结果显示,16份组织样品均为阳性。在443 nt VP1区,所测8株病毒之间的序列同源性为100%,与GPV亚洲强毒分支之间的序列同源性为99%。随后,用琼脂扩散沉淀试验分析了2株待检毒株与GPV参考毒株的抗原相关性,并测定了2种小鹅瘟蛋黄抗体产品的效价。结果显示,待检毒株与参考毒株具有相同的沉淀抗原,2种小鹅瘟蛋黄抗体产品的效价分别为1∶2和1∶16。表明免疫雏鹅仍发生小鹅瘟的原因并非源自GPV变异,而是与某些蛋黄抗体产品的抗体效价较低有关。

In June 2018,gosling plague was reported from Anhui province in two flocks of goslings immunized with gosling plaque yolk antibody preparation at one day of age.Mortality couldn’t be controlled thoroughly by urgent immunization with gosling plaque yolk antibody preparation.To analyze the reasons of failure,both liver and spleen samples were collected from eight 9 to 12 day-old dead goslings from the affected flocks for molecular detection by using a waterfowl parvovirus PCR targeting the VP3 gene.Characterization included nucleotide sequence determination and analysis of the VP1-specific DNA fragments amplified from eight positive samples.Using the VP3-based PCR assay,all 16 tissue samples were tested positive.Sequence analysis of a 443-nt VP1 sequence showed that the eight GPV strains were 100%identical to one another and 99%identical to members of the Asian virulent lineage of GPV.Subsequently,agar gel precipitin test was employed to investigate the antigenic relationship between two selected viral strains with the reference GPV,and to determine the titers of two gosling plague yolk antibody preparations.The two viral strains were shown to share identical precipitation antigen with the reference GPV.The titers of the two gosling plague yolk antibody preparations were 1∶2 and 1∶16,respectively.Together data suggest that the occurrence of the disease in immunized goslings might attribute to the lower antibody titer of some yolk antibody preparations,rather than variation of GPV.