Newcastle disease virus in Taiwan: II, Relationship between polykaryocytosis and virus virulence.

Fifteen selcted local isolates and five known Newcastle disease virus strains were examined for their cytopathic effects in chick embryo kidney (CEK) cells, egg-infectious units in chick embryos (CE), virulence by mean death time, intracerebral and intravenous pathogenicity indexes for CE and chicks, and ability to cause polykaryocytosis of fusion from within (FFWI) or fusion from without (FFWO) in CEK and BHK-21 monolayer cells. The capacity of the different virus strains to induce cell FFWI at 15 hr post-infection was related to their virulence for CE and chicks, but cell FFWO did not seem to be any relationship with the virulence of the strains.