Capsid protein sequence diversity of avian nephritis virus

The capsid gene sequences of 25 avian nephritis viruses (ANVs), collected in the UK, Germany and Belgium from the 1980s to 2008, were determined and compared with those of serotype 1 (ANV-1) and serotype 2 (ANV-2) ANV isolates. Amino acid identities as low as 51% were determined. Pairwise comparisons supported by phylogenetic analysis identified six ANVs, including ANV-1 and ANV-2, which shared<80% amino acid identities with one another, and which were selected to be representative of six groups. The ANVs were not distributed according to geographical location or year of sampling, and the detection of ANVs from five different groups in 11 samples sourced from six flocks belonging to the same UK organization within a 4-month period indicated that sequence-diverse ANVs were co-circulating. Amino acid alignments demonstrated the existence of variable regions throughout the capsid protein, nine of which were selected for detailed comparisons. With most ANVs, the variable region sequences were similar to those of one of the six representative ANVs, but some ANV capsids displayed novel variable region profiles, in which variable regions that were characteristic of more than one representative ANV were present. Phylogenetic analysis based on C-terminal sequences of approximately 260 amino acids and SimPlot analysis provided evidence that RNA recombination events located in the 1250 to 1350 nucleotide region resulted in new combinations of the N-terminal and C-terminal capsid regions. The high level of capsid sequence diversity observed in the present study has important implications for both the control and diagnosis of ANV infections.