To comfirm the cause of a disease characterized by white spotty necrosis of liver in a mallard duck flock that oc-curred from a farm in Zhejiang province in 2020,diseased duck tissues were detected and identified for the pathogen,and patho-genicity tests were carried out with partridge duck.The results showed that the pathogen was identified as fowl adenovirus sero-type 4(FAdV-4),named as QZ20 strain.The isolate was in the same branch as FAdV-4 strains which were prevalent in China in recent years,and the nucleotide sequence homology reached 98%-100%.QZ20 strain infected chicken liver hepatocellular carci-noma cell line(LMH)could produce a cytopathic effect(CPE)and was able to proliferate in LMH cells,the TCID50 of which was 105.5/0.1 mL.The body of chicken embryos inoculated QZ20 isolate was flushed,the whole body was bled diffusely,even the chicken embryos were killed.Pathological changes in the duodenum,liver and kidney were observed in 1-day-age partridge ducklings infected by QZ20 strain.The study indicated that a strain of FAdV-4 was successfully isolated from infected partridge duck and slightly different from FAdV-4 strains circulating in Chinese chickens,and the results provided a basis for the epidemi-ological investigation and control of FAdV-4.
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