Genetic characterization of novel fowl aviadenovirus 4 isolates from outbreaks of hepatitis-hydropericardium syndrome in broiler chickens in China

Abstract

Since May 2015, severe outbreaks of hepatitis-hydropericardium syndrome (HHS) associated with infections of fowl aviadenovirus (FAdV) have emerged in broiler chickens in several Chinese provinces. To identify the genotype and gain a better understanding of the genetic properties of the FAdV strains responsible for the recent HHS outbreaks in China, the complete genome sequences of five isolates from outbreaks of HHS in broiler chickens in five provinces were determined. The results demonstrated that a novel fowl aviadenovirus 4 (FAdV-4) genotype was epidemic in China. To investigate the molecular characteristics of these Chinese FAdV-4 isolates, their genome contents were compared with those of reported pathogenic and non-pathogenic FAdV-4 strains. The comparative analysis revealed that the novel Chinese FAdV-4 isolates contain various genomic deletions and multiple distinct amino-acid mutations in their major structural genes. Two additional putative genetic virulence markers in the fiber 2 gene were identified. These findings confirmed some of the genetic differences between the pathogenic and non-pathogenic FAdV-4 isolates. The data presented in this report will enhance the current understanding of the molecular epidemiology and genetic diversity of FAdV-4 isolates in China and will provide additional insight into the critical factors that determine the pathogenicity of FAdV-4 strains. Finally, the emergence of this novel and highly pathogenic FAdV-4 genotype emphasizes that preventive measures against FAdV-4 infections on poultry farms should be implemented in China.

Figure 1

Postmortem and histological examinations of the liver and heart from affected birds with hepatitis-hydropericardium syndrome (HHS). (A) The accumulation of clear, straw-colored fluid in the pericardial sac and a discolored swollen liver with pinpoint hemorrhage. (B) Small multifocal areas of necrosis and basophilic intranuclear inclusion bodies in hepatocytes (H&E stain, original magnification × 400, scale bar=50 μm). (C) Lymphocytic infiltrates in association with myocarditis (H&E stain, original magnification × 400, scale bar=50 μm).

Figure 2

A comparison of the complete genomes among Chinese fowl aviadenovirus 4 (FAdV-4) strains and the previously reported sequences of highly pathogenic and non-pathogenic FAdV-4 strains. Insertions in the GA and TC repeat regions and deletions in the 22 kDa protein, ORF19, ORF27, ORF19A and tandem repeat (TR) E regions are shown. Open reading frames (ORFs).

Figure 3

The results of phylogenetic analyses based on the nucleotide sequences of the currently available complete genomes (A), fiber 1 (B), fiber 2 (C) and hexon (D) gene sequences of FAdV-4 isolates and representative genes of other FAdV species. The trees were generated by the maximum-likelihood method with bootstrap tests of 1000 replicates using the MEGA 6.06 software. Bootstrap values are presented at key nodes. The scale bars indicate the nucleotide substitutions per site. Filled circles indicate HHS-inducing FAdV-4 strains. Open circles indicate non-HHS-inducing strains. Hepatitis-hydropericardium syndrome (HHS).