Thirty-eight virus strains were isolated from affected chicks in Weifang, Qingdao, Yantai, Binzhou, Zibo, Dezhou, Heze, Linyi of Shangdong province using specific pathogen free (SPF) chick embryos These isolates are able to agglutinate chick red blood cell. Thirty-two virus strains of them were characterized as Newcastle disease virus (NDV) by hemagglutination (HA) /hemagglutination-inhibition (HI) test. The biological characteristics of these viruses were determined by measuring the mean death ...