The biology of avipoxvirus in New Zealand avifauna : a thesis presented in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Veterinary Pathology at Massey University, Palmerston North, New Zealand
Avipoxvirus (APV) infection is a highly contagious disease of birds which is comparable
to poxvirus infections in various mammalian species, including smallpox in humans.
The infection has been reported in more than 200 bird species, affecting both
domesticated and free-ranging birds around the world. The disease is associated with
economic loss in the poultry industry and is implicated with the decline in biodiversity
in free-ranging birds, particularly in island ecosystems. This study was the first
investigation into APV infection in New Zealand free-ranging birds. The initial focus of
this study was the phylogenetic analysis of APV in New Zealand. Avipoxvirus antibody
was then detected using enzyme-linked immunosorbent assay (ELISA) in several
introduced species and an endemic passerine species in New Zealand. The
pathogenicity of two major APV strains isolated from New Zealand birds was evaluated
and the safety and efficacy of a commercial fowlpox (FWPV) vaccine was investigated in
a model passerine species.
This study confirms that various New Zealand birds including endangered species are
susceptible to APV infection and that at least three different strains of APV are present
in New Zealand, with overlaps in the geographic distributions between different strains.
The results suggest that APV had been introduced to New Zealand through avian hosts,
insect vectors or human intervention such as poultry vaccination. A high
seroprevalence to APV has been observed in introduced and an endemic bird species in
New Zealand, confirming that the virus is well established. A significant relationship
between birds seropositive to APV and the ones positive to Plasmodium spp. has also
been observed, both of which are known to be pathogens responsible for dramatic
declines in island bird populations. Two major New Zealand APV strains isolated from
clinical cases were pathogenic in Zebra finches (Taeniopygia guttata), which we used as
a model passerine species. A commercial FWPV vaccine was safe and effective in our
model species against New Zealand APV isolates and I conclude that vaccination of
native passerine birds using the FWPV vaccine could be an effective tool to reduce APV
mortality, particularly in endangered species.