Virus isolation
The liver sample (ZaoZhuang County) from Shandong province was selected for virus isolation. After five passages, an astrovirus designated as DAstV/SDZZ/Duck (DAStV-SDZZ) strain, was successfully isolated. Most inoculated cells showed CPE after inoculation within 72–96 hr and tested positive for DAStV-1 by RT-PCR using the above primers.