Genetic diversity and pathogenicity of novel chicken astrovirus in China

Five novel chicken astrovirus (CAstV) strains, designated ZDF, MHC, WSC, WSW and MHW, were successfully isolated from chickens with gout, and were subjected to full genome sequencing characterization and tested for their pathogenic effects in specific pathogen-free (SPF) chicken embryos and chickens. The complete genomes of the five isolated strains were approximately 7436 nt to 7511 nt in length. Phylogenetic analysis revealed that strains ZDF and MHC were clustered in a clade with strains isolated in China and that the others were clustered with strains from other countries. Based on the amino acids of ORF2, strains MHW and WSW belonged to subgroup Ai, strain WSC belonged to Bii, and strains ZDF and MHC belonged to Bi. The pathogenicity of strains MHW, MHC and WSC, all belonging to different subgroups was studied. The results showed that the mortality of the chicken embryos was 100% when infected with any strain at a dose of more than 10³ TCID₅₀, 35% in SPF chickens infected with strain WSC, 25% with MHC and 15% with MHW. The body weights of chickens and embryos infected with 0.2 ml 10 TCID₅₀ were significantly reduced after hatching. SPF chickens infected with any of the strains had similar lesions characterized by urate deposits on the epicardium and kidney, and necrotic spots on the liver. This study identified the three types of genotypic CAstV prevalent in China, with high mortality in embryonated chicken eggs and leading to white chick syndrome, retarded growth and visceral gout in infected chicks.