Isolation and identification of high virulent strains of Newcastle disease virus

Eight isolates having haemaggluting property have been isolated from the disease-infected chicken houses in Hebei, Tianjin, Beijing, etc, the haemaggluting property of the eight isolates can be inhibited by the positive antiserum of Newcastle disease virus, not by the positive serum of AIV (H9 subtype), EDS76, which shows that these eight isolates are Newcastle disease virus. They have been cloned by the method of limited-point dilution using chicken embryos. The results of pathogenicity tests (MDT, ICPI, IVPI ) show that the eight strains of NDV claim these data: MDT, 42.9～49.5 h; ICPI, 1.95～2.00; IVPI, 2.68～2.89, which indicates that these eight NDV isolates are all high virulent,the virulence is almost the same with the standard high virulent NDV-F_48E_8. Different forms of particles such as filamentous, rounded, irregular can be seen through the electron microscope when the particles have been stained negatively by 2% phosphatungstenic acid, and the surfaces of the strains are observed to have spike-like structures. Different strains have different sizes with diameters or long-axis ranging from 100 to 500 nm.