Fowl adenovirus species C serotype 4 is attributed to the emergence of hepatitis-hydropericardium syndrome in chickens in China

Since July in 2015, an emerging infectious disease of Hepatitis-Hydropericardium syndrome (HHS) was prevalent in chicken flocks in China. To confirm the causative agent and investigate the epidemiology of the disease, a total of 38 chicken flocks including 187 samples from Jilin, Liaoning, Heilongjiang, Henan, Anhui, Hubei, Jiangxi, Xinjiang, Shandong and Hunan provinces in China were collected and determined by PCR detection, sequencing, phylogenetic analysis and virus isolation. 81 samples (positive rate of samples, 81/187, 43.3%) distributed in 33 chicken flocks (positive rate of chicken flocks, 33/38, 86.8%) were detected to be positive for fowl adenovirus (FAdV) by PCR method, of which 30 were determined as FAdV species C, 41 were species D, 9 were species E and 1 was uncertain for the viral species by phylogenetic analysis, implicating that at least three species (C, D and E) of FAdVs were prevalent in China and the species C and D were predominantly the prevalent viral strains. Interestingly, our results indicated that two types of FAdVs (C and D) co-existed in one flock, resulting in complex condition for the prevalence of the disease. In addition, 13 viral strains of FAdV-C were isolated from different geographic areas and one of the isolates from Henan province, designated HN/151025 strain, was inoculated into 40-day-old specific pathogen free chickens via intramuscular or oral route to evaluate the pathogenicity. It was found that 90% (9/10) chickens died in the intramuscular injection group and 30% (3/10) birds died in the oral route infection group after challenge. Histopathology examination displayed that the pathology confined to liver, kidney, spleen, and heart. These results indicated that the virus was a highly virulent strain.