SKIC2 and Newcastle disease: The W protein sequence analysis of nearly 1000 strains of APMV-1 in our lab show variations in the W protein length between strains (unpublished data),which was also reported recently in an analysis of 286 strains of NDV91, furthermore, W proteins of only about 50% of the strains analyzed by us are predicted to localize into the nucleus (data not shown) leading us to speculate that these differences in W proteins can attribute to the wide spectrum of pathogenicity and virulence observed in Newcastle disease.