Isolation, identification and molecular characteristics of group I fowl adenovirus serotype 4 from Guangdong, China

Objective  To isolate and identify the pathogen causing the inclusion body hepatitis (IBH) and hydropericardium syndrome (HPS) in chicken in Guangdong Province, and study its molecular characteristics.

Method  A virus was isolated from specific pathogen-free(SPF) chicken embryo inoculated with liver suspension from affected chickens. The virus was purified by limiting dilution method and used for pathogenicity test. Hexon, fiber-2, ORF29 and ORF19 genes were amplified by PCR, and analyzed for molecular characteristics.

Result  Sequence analysis of hexon gene revealed the strain, named as WM-XC, belonged to group I fowl adenovirus serotype 4 (FAdV-4). This isolated strain was pathogenic based on the evidence that the mortality rate of SPF chicken reached 90% after virus inoculation, the hydropericardium-hepatitis syndrome was observed, and acidophilous inclusion body was found in the pathological section of liver. The fiber-2 gene sequence of WM-XC had 96.1% and 97.0% similarities with the corresponding sequences of ON1 and KR-5, and had 100% similarity with fiber-2 genes of fowl adenovirus isolates collected in China since 2015. There was a 33 bp deletion in ORF29 gene of WM-XC compared with JSJ13 and JN13 strains isolated in 2013 in China. Similar to isolates collected in China since 2015, WM-XC lacked ORF19 compared with classical FAdV-4 strain ON1 and KR-5.

Conclusion  The isolated group I FAdV-4 strain and other isolates collected in China in recent years were distinct from classical FAdV-4 strains in their fiber-2, ORF19 and ORF29 gene sequences.