Avihepadnavirus diversity in parrots is comparable to that found amongst all other avian species.

Avihepadnaviruses have previously been isolated from various species of duck, goose, stork, heron and crane. Recently the first parrot avihepadnavirus was isolated from a Ring-necked Parakeet in Poland. In this study, 41 psittacine liver samples archived in Poland over the last nine years were tested for presence of Parrot hepatitis B virus (PHBV). We cloned and sequenced PHBV isolates from 18 birds including a Crimson Rosella, an African grey parrot and sixteen Ring-necked Parakeets. PHBV isolates display a degree of diversity (>78% genome wide pairwise identity) that is comparable to that found amongst all other avihepadnaviruses (>79% genome wide pairwise identity). The PHBV viruses can be subdivided into seven genetically distinct groups (tentatively named A-G) of which the two isolated of PHBV-G are the most divergent sharing ∼79% genome wide pairwise identity with all their PHBVs. All PHBV isolates display classical avihepadnavirus genome architecture.

Identification of interspecies recombination among hepadnaviruses infecting cross-species hosts.

Members of the family Hepadnaviridae are divided into two genera, Orthohepadnavirus (from mammalian) and Avihepadnavirus (from avian). Recombination had been found to occur among human hepatitis B virus (HBV) strains of different genotypes, or between hepadnavirus strains from human and nonhuman primate. To reach a comparatively complete inspection of interspecies recombination events among hepadnavirus strains from various hosts, 837 hepadnavirus complete genome sequences from human and 112 from animals were analyzed by using fragment typing to scan for potential interspecies recombinants. Further bootscanning and phylogenetic analyses of the potential recombinants revealed six genome sequences as interspecies recombinants. Interspecies recombination events were found to occur among HBV strains from human and nonhuman primates, from gibbons of different genera, from chimpanzee and an unknown host, and between two avian hepadnavirus strains from birds of different subfamilies, which was identified for the first time. HBV interspecies recombinants were found to have recombination hot spots similar to that of human HBV intergenotype recombinants, breakpoints frequently locating near gene boundaries. Interspecies recombination found in this study may alter current views on hepadnavirus host specificity.

Hepatitis B virus taxonomy and hepatitis B virus genotypes.

Hepatitis B virus (HBV) is a member of the hepadnavirus family. Hepadnaviruses can be found in both mammals (orthohepadnaviruses) and birds (avihepadnaviruses). The genetic variability of HBV is very high. There are eight genotypes of HBV and three clades of HBV isolates from apes that appear to be additional genotypes of HBV. Most genotypes are now divided into subgenotypes with distinct virological and epidemiological properties. In addition, recombination among HBV genotypes increases the variability of HBV. This review summarises current knowledge of the epidemiology of genetic variability in hepadnaviruses and, due to rapid progress in the field, updates several recent reviews on HBV genotypes and subgenotypes.

Identification and characterization of avihepadnaviruses isolated from exotic anseriformes maintained in captivity.

Five new hepadnaviruses were cloned from exotic ducks and geese, including the Chiloe wigeon, mandarin duck, puna teal, Orinoco sheldgoose, and ashy-headed sheldgoose. Sequence comparisons revealed that all but the mandarin duck viruses were closely related to existing isolates of duck hepatitis B virus (DHBV), while mandarin duck virus clones were closely related to Ross goose hepatitis B virus. Nonetheless, the S protein, core protein, and functional domains of the Pol protein were highly conserved in all of the new isolates. The Chiloe wigeon and puna teal hepatitis B viruses, the two new isolates most closely related to DHBV, also lacked an AUG start codon at the beginning of their X open reading frame (ORF). But as previously reported for the heron, Ross goose, and stork hepatitis B viruses, an AUG codon was found near the beginning of the X ORF of the mandarin duck, Orinoco, and ashy-headed sheldgoose viruses. In all of the new isolates, the X ORF ended with a stop codon at the same position. All of the cloned viruses replicated when transfected into the LMH line of chicken hepatoma cells. Significant differences between the new isolates and between these and previously reported isolates were detected in the pre-S domain of the viral envelope protein, which is believed to determine viral host range. Despite this, all of the new isolates were infectious for primary cultures of Pekin duck hepatocytes, and infectivity in young Pekin ducks was demonstrated for all but the ashy-headed sheldgoose isolate.

Identification and analysis of a new hepadnavirus in white storks.

We identified, cloned, and functionally characterized a new avian hepadnavirus infecting storks (STHBV). STHBV has the largest DNA genome of all avian hepadnaviruses and, based on sequence and phylogenetic analysis, is most closely related to, but distinct from, heron hepatitis B virus (HHBV). Unique for STHBV among the other avian hepadnaviruses is a potential HNF1 binding site in the preS promoter. In common only with HHBV, STHBV has a myristylation signal on the S and not the preS protein, two C terminally located glycosylation sites on the precore/core proteins and lacks the phosphorylation site essential for the transcriptional transactivation activity of duck-HBV preS protein. The cloned STHBV genomes were competent in gene expression, replication, and viral particle secretion. STHBV infected primary duck hepatocytes very inefficiently suggesting a restricted host range, similar to other hepadnaviruses. This discovery of stork infections unravels novel evolutionary aspects of hepadnaviruses and provides new opportunities for hepadnavirus research.