Updates on Beak and Feather Disease virus

A focus of recent research into PBFD has been to investigate evolutionary pathways of BFDV in Australasian parrots and cockatoos with the aim to identify potential BFDV clades that might threaten endangered host species. Emerging consensus
indicates that Australian parrots are susceptible to a diversity of BFDV clades with no clear association based on host-virus co-speciation. The latest phylogeny of BFDV in parrot species throughout Australia is important for understanding the likely threats to vulnerable and endangered psittacine bird species such as the orange-bellied parrot ( Neophema chrysogaste), wstern ground parrot (Pezoropus flaviventris), swift parrot ( Lathamus disco.for) and regent parrot (Polytelis anthopeplus monarchoides). The latest results indicate that all endangered Australian psittacine bird species are equally likely to be infected by BFDV genotypes from any other close or distantly related host reservoir species. In the context of BFOV in the Australian landscape the involvement of (multiple and unknown alternative host species is a well recognised major confounder for wildlife disease modelling. Host population thresholds for the invasion or persistence of infectious disease, core concepts of disease ecology, have formed the basis of disease control policies. However, a definitive understanding of population thresholds for a multi-host disease such as PBFD is likely to never be resolved given the large number of potential host species and conceivable parameters which could dynamically influence intra and
interspecific transmission rates, alongside other factors such as abundance of important host reservoir species. Nevertheless, the phylogenetic analysis of BFDV genomes strongly indicates that no one genotype can be considered as more virulent
than another and as such it behaves like a viral quasispecies and host-generalist in the Psittaciformes, with shallow host-based divergence likely reflecting dynamic ranges of interspecific transmission. Increasing evidence supports a post-Gondwanan origin of BFDV in Australian species where the virus now exists as a pathogenic host­ generalist quasipecies capable of flexible host-switching amongst the psittacid avifauna of Australia and there ,is fossil evidence that Cacatua and the budgerigar have likely been present in Australia in their present forms for at least 5 million years. It is theoretically likely that BFDV has circulated as a quasispecies with limited host-based divergence amongst Australian Psittaciformes for at least this period. In contrast there is no strong evidence BFDV endemicity in native New Zealand parrot species prior to human colonisation and the recent detection of PBFD in wild New Zealand birds is explainable by the introduction of this pathogen with the release of infected feral eastern rosellas ( Platycercus eximius) from Australia. A similar scenario almost certainly occurred for the Norfolk Island green parrot.