Identification and characterization of avian hepatitis E virus in 2013 outbreaks of hepatitis-splenomegaly syndrome in two United States layer operations

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 in Farm A and in 46-week-old hens in Farm B. Average weekly mortality was 0.44% over a 4-week period in Farm A and 0.17% over an 8-week period in 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 to standard egg production curves (p <0.01) while no decrease in egg production was noticed in Farm B. Postmortem examination revealed changes consistent with hepatitis-splenomegaly syndrome, including hepatomegaly with serosanguineous fluid in the coelomic cavity and hepatic subcapsular hemorrhages. Microscopic lesions were characterized by multifocal necrotizing hepatitis and intrahepatic hemorrhage. No significant bacteria were recovered from liver samples, but 72.0-100% of the liver samples from affected chickens in 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 98.6-100% nucleotide identity between the aHEV genomes from Farm A and Farm B, whereas identities ranged from 74.6-90.5% when compared to other representative sequences. Sequences from this study clustered within aHEV genotype 2 previously recognized in the USA. In contrast to other reported aHEV outbreaks which occurred in 30 to 80-week-old-chickens, in the present investigation clinical aHEV was identified in 17week-old chickens in one of the farms. Ac ce pte M an us cri pt D ow nl oa de d by [ U ni ve rs ity o f E di nb ur gh ] at 0 1: 33 1 6 Ju ly 2 01 4