Molecular characterization of a recently identified circovirus in zebra finches (Taeniopygia guttata) associated with immunosuppression and opportunistic infections.

A recently identified circovirus (family Circoviridae) was detected in 14 zebra finches (Taeniopygia guttata) from seven aviaries and hobbyist breeders using polymerase chain reaction followed by sequencing. Full genome sequences of virus strains from six zebra finches consistently revealed characteristic circoviral genomic features such as a stem-loop structure and two major open reading frames (ORFs) encoding the replication-associated protein and the putative capsid protein. One further ORF encoding a protein of unknown function was additionally identified in all six genomes. Based on full genome nucleotide comparison, zebra finch circovirus was most similar to Finch circovirus originating from a Gouldian finch (Chloebia gouldiae) sharing 78% nucleotide identity. High genetic diversity was detected in the circoviruses from individual zebra finches. Comparison of the six full genome sequences revealed two genetic subgroups, which shared pairwise nucleotide identities between 91.4% and 92.7%. Analyses including partial sequences of the replication-associated protein gene of the zebra finch circovirus strains from all 14 birds supported the existence of two main clusters. Clinical diseases associated with circovirus infection were found in nestlings, fledglings and adult birds and varied from mild to severe with high mortality caused by secondary infections. Macrorhabdus ornithogaster was the most frequently detected opportunistic pathogen. Feathering disorders were seen in two birds. Lymphocytic depletion of the spleen and leukocytopaenia were detected in individual birds, suggesting immunosuppression and a pathogenesis common to circovirus infections in other birds.