Hi Michelle,
I can't say definitively why there is increased prevalence at this
time of year, but I suspect it is related to the large numbers of
juvenile parrots that begin seeking (are forced into?) independence
around this time. Many of the cockatoos that come in to the wildlife
hospital are young birds, and it is almost certain that the disease is
transmitted by the parents to young parrots while they are in the nest.
It is possible that, as the birds mature, the disease progresses as
well such that recently fledged birds are in the most acute stages of
the disease. The PBFD virus causes immune deficiency (amongst other
things), rendering the young parrots susceptible to all sorts of other
diseases as well. I think that contact with flocks of conspecifics
would permit further transmission of the virus before the diseased
birds become too ill to fly or feed.
I have been told (and I have been unable to substantiate this) that
the virus is always present in many individuals (both adults and
juveniles), but if the bird becomes stressed then the virus becomes
problematic. I guess in some ways this is like a few other viruses
that affect humans (herpes and HIV). I don't know what the stress
triggers would be, but I imagine leaving the nest, finding food and
water, and interacting with flocks of conspecifics may qualify.
It appears that Dr Gary Cross from the University of Sydney was
researching the disease over 15 years ago, and according to a website (http://www.parrotsociety.org.au/articles/art_007.htm
) a vaccine was developed. This vaccine was used to innoculate
populations of OBP's (see http://www.environment.gov.au/biodiversity/threatened/ktp/pcd.html)
, and apparently those birds are still resistant to the virus (which
is good news). I have no idea if any further research is being
conducted, but I think the increased prevalence (and fatality) in
juvenile parrots would make an interesting PhD project for someone.
As I said in my first email, I'm not an expert by any stretch of the
imagination. My background is zoological (frogs, in fact) so I'd be
very interested to hear from anyone else out there on Birding Aus who
may know more about PBFD.
Cheers,
Beth.
~~~~~~~~~~~
Beth Mantle
H: 02 6287 7860
M: 0407 174 427
E:
On 25/04/2008, at 9:14 AM, Michelle Plant wrote:
Beth,
Any indication/suggestions of why there is increased prevalence?
Regards
Michelle
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