Gerber Priscilla F, Trampel Darrell W, Opriessnig Tanja
a Department of Veterinary Diagnostic and Production Animal Medicine , College of Veterinary Medicine, Iowa State University , Ames , IA , USA.
Avian Pathol. 2014;43(4):357-63. doi: 10.1080/03079457.2014.935755. Epub 2014 Jul 21.
Two commercial Midwestern egg-type chicken flocks experienced significant increases in mortality rates in April 2013 with clinical signs appearing in 17-week-old pullets on Farm A and in 46-week-old hens on Farm B. Average weekly mortality was 0.44% over a 4-week period on Farm A and 0.17% over an 8-week period on Farm B. On Farm A, flocks in the affected house had a 45% decrease in daily egg production from weeks 19 to 27 when compared with standard egg production curves (P < 0.01) while no decrease in egg production was noticed on Farm B. Post-mortem examination revealed changes consistent with hepatitis-splenomegaly syndrome, including hepatomegaly with serosanguineous fluid in the coelomic cavity and hepatic subcapsular haemorrhages. Microscopic lesions were characterized by multifocal necrotizing hepatitis and intrahepatic haemorrhage. No significant bacteria were recovered from liver samples, but 72 to 100% of the liver samples from affected chickens on Farm A (8/11) and Farm B (7/7) contained detectable amounts of avian hepatitis E virus (aHEV) RNA as determined by polymerase chain reaction. Sequencing and phylogenetic analysis of a 361-base-pair fragment of the helicase gene demonstrated 98.6 to 100% nucleotide identity between the aHEV genomes from Farm A and Farm B, whereas identities ranged from 74.6 to 90.5% when compared with other representative sequences. Sequences from this study clustered within aHEV genotype 2 previously recognized in the USA. In contrast to other reported aHEV outbreaks that occurred in 30-week-old to 80-week-old chickens, in the present investigation clinical aHEV was identified in 17-week-old chickens on one of the farms.
2013年4月，美国中西部的两个商业化蛋鸡群死亡率显著上升，A农场17周龄的小母鸡和B农场46周龄的母鸡出现了临床症状。A农场在4周内的平均周死亡率为0.44%，B农场在8周内的平均周死亡率为0.17%。在A农场，与标准产蛋曲线相比，受影响鸡舍的鸡群在第19至27周的日产蛋量下降了45%（P<0.01），而B农场未观察到产蛋量下降。尸检发现与肝炎-脾肿大综合征一致的变化，包括肝脏肿大、体腔中有血清样液体以及肝包膜下出血。显微镜下病变特征为多灶性坏死性肝炎和肝内出血。肝脏样本中未分离到重要细菌，但通过聚合酶链反应测定，A农场（8/11）和B农场（7/7）受影响鸡的肝脏样本中有72%至100%含有可检测量的禽戊型肝炎病毒（aHEV）RNA。对解旋酶基因361个碱基对片段的测序和系统发育分析表明，A农场和B农场的aHEV基因组之间的核苷酸同一性为98.6%至100%，而与其他代表性序列相比，同一性范围为74.6%至90.5%。本研究的序列聚集在美国先前确认的aHEV基因型2内。与其他报道的发生在30周龄至80周龄鸡身上的aHEV疫情不同，在本次调查中，在其中一个农场的17周龄鸡中发现了临床aHEV。
