Evaluation of the genetic diversity of avian paramyxovirus type 4

Avian paramyxoviruses (APMVs) belong to the genus Avulavirus in the family Paramyxoviridae and include at least nine serotypes, APMV-1 to -9, as well as two additional provisional serotypes. Newcastle disease virus (NDV), which comprises APMV-1, is the most extensively studied APMV because it is an important poultry pathogen. A moderate level of antigenic and genetic diversity is recognized for APMV-1 isolates, but our knowledge of the antigenic and genetic diversity of the other APMV serotypes is limited. APMV-4 is frequently isolated from waterfowl around the world. To date complete genome sequences of APMV-4 are available for only strains, which were isolated from ducks in Hong Kong, Korea and Belgium over a period of 37 years. We have carried out genome sequencing from the nucleocapsid (N) gene-end signal to the polymerase (L) gene-start signal of five APMV-4 strains recently isolated from Italy. Each of the eight APMV-4 strains has the same F protein cleavage site, DIQPR↓F. They also share a high level of nucleotide and amino acid sequence identity: for example, the F and HN glycoproteins have greater than 97% sequence identity between the various strains. Thus, comparison of these eight strains of APMV-4 did not provide evidence of substantial diversity, in contrast to similar studies with APMV-2, -3, and -6, in which the F and HN glycoproteins exhibited up to 20–30% amino acid sequence variation within a subgroup. Reciprocal cross-HI assay using post infection chicken sera also failed to detect significant antigenic variation among the available APMV-4 strains.