Beak and feather disease virus (BFDV), a non-enveloped, icosahedral virus with a circular single
stranded DNA (ssDNA) genome, is the causative agent behind psittacine beak and feather disease
(PBFD), an often fatal disease affecting parrots. Symptoms include feathering abnormalities, loss of
feathers, and occasionally beak and claw deformities. BFDV-induced immunosuppression results in
an increased susceptibility to secondary microbial infections, which is often the cause of death in
infected parrots. There is no cure, no effective treatment, and no protective vaccine for BFDV. The
international trade in exotic parrots has facilitated the spread of BFDV, so that it now has a global
presence. Given that over a quarter of the currently recognised 356 psittacine species are
considered to be at risk of extinction in the wild, the worldwide presence of BFDV, coupled with its
extreme environmental stability, poses serious concerns for the future of some of the worlds most
endangered parrots.
That genetic diversity exists among BFDV isolates has been established, yet in the 14 years since the
genome was fully sequenced, very few full-length BFDV genome sequences have been deposited in
GenBank, despite the technology to rapidly isolate and amplify entire circular ssDNA genomes being
readily available. Most studies have sequenced just a portion of the genome, usually one of the open
reading frames (ORFs) encoding the major viral proteins, to investigate phylogenetic relationships
between isolates. However the two major BFDV ORFs, encoding the replication associated protein
(Rep) and the capsid protein (CP), have been shown to evolve at different rates, with the functional
Rep being generally more conserved while CP is more variable. When also considering the fact that
ssDNA viruses are notoriously recombinant, it becomes clear that an analysis based on a portion of
the genome is unlikely to accurately establish evolutionary relationships. Therefore the focus of the
studies described in this thesis was on isolation and amplification of full-length BFDV genomes from
avian blood and feather samples that first tested positive to a PCR-based BFDV screening method.
Samples were collected by appropriately trained people in New Zealand, New Caledonia, and
Poland, before being sent to the University of Canterbury for molecular and bioinformatic analysis.
The sequences of the BFDV genomes from each region were compared to each other and to all other
full BFDV genome sequences publically available in GenBank, to compare the genetic diversity
among these isolates. Recombination analyses were also performed, to assess how recombination is
impacting on the evolution of BFDV.
New strains of BFDV and new subtypes of existing BFDV strains were discovered, indicating that the
global genetic diversity may be greater than previously thought. Many strains also proved to be
recombinants, in particular those from Poland. Europe has had a long history with importing and
breeding exotic parrots, and the high degree of recombination among the Polish BFDV isolates
coupled with the number of previously unsampled strains is an example of how maintaining
populations of multiple species in captivity enables evolution through recombination, and
emergence of novel viral strains.
Full genome analyses can also enable tracking the source of an infection. A total of 78 full genome
sequences from 487 samples tested were deposited into GenBank as a direct result of the work
undertaken as part of this thesis, thereby adding to the existing knowledge base regarding BFDV.
With continued global sampling and full genome analysis it may one day be possible to trace the
history of BFDV to its original emergence.
| Identifer | oai:union.ndltd.org:canterbury.ac.nz/oai:ir.canterbury.ac.nz:10092/7425 |
| Date | January 2012 |
| Creators | Julian, Laurel |
| Publisher | University of Canterbury. Biological Sciences |
| Source Sets | University of Canterbury |
| Language | English |
| Detected Language | English |
| Type | Electronic thesis or dissertation, Text |
| Rights | Copyright Laurel Julian, http://library.canterbury.ac.nz/thesis/etheses_copyright.shtml |
| Relation | NZCU |
Page generated in 0.002 seconds