Isolation and Identification of High Virulent Newcastle Disease Virus in Shandong Province

isolates of viruses were isolated from 7 chicken flocks with high morbidity and mortality cotagious disease.These isolates are able to agglutinate chicken red blood cell which can be inhibited by Newcastle disease virus La Sota strain standard antisera,but cannot be neutralized by the antisera,they were still able to kill chicken embryos.These isolates were confirmed to be Newcastle disease virus based on 50% embryo lethal dose (ELD 50),mean death time (MDT) of chicken embryos,intracerebral pathogenicity index (ICPI) in 1-day-old chickens,intravenous pathogenicity index (IVPI) in 6-week-old chickens,dehaemagglutination and haemagglutinin heat-stability.The results demonstrated that these isolates were high virulent Newcastle disease virus,which were virulent as similar as F 48E 9 strain.