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Proventricular
Dilitation
Disease
In the early to mid 1970's, a new syndrome was recognized
in a group of Bolivian import Blue and Gold Macaws. This disease was
characterized by regurgitation, passage of whole seeds in the droppings,
diarrhea, and secondary bacterial infections.
Progressive weight loss always resulted, even if there was a normal
appetite and these birds invariably died regardless of numerous types of
attempted treatments. Appropriately,
this condition was then termed Macaw Wasting Disease - because of the
progressive weight loss and the species affected.
Internally, the affected portion of the digestive tract was usually the
proventriculus (the portion just in front of the gizzard), which was usually
significantly dilated, unable to contract, and therefore, could not move food
through the digestive system normally.
Macaw Wasting Disease, more properly termed Proventricular
Dilitation Disease (PDD), is now recognized worldwide, and is a problem in both
hand fed domestic as well as imported psittacine birds. Multiple species of
psittacine birds are now commonly afflicted with this disease, and it has also
been recognized in finches, waterfowl, roseate spoonbills and toucans as well.
As such, Proventricular Dilitation Disease poses a significant threat to the pet
psittacine bird as well as the breeding or avicultural collection.
It is believed that Proventricular Dilitation Disease is
caused by a virus, although there has been no successful attempts to isolate
this agent at the present time. An unnamed RNA virus has been identified
recently as a potentially causative agent of this disease, and further work to
develop a reliable test for it in potentially afflicted birds is currently
underway.
There are numerous clinical accounts supportive of an
infectious and contagious nature of this disease.
One colleague reports a single household situation in which one newly
acquired Blue and Gold Macaw developed symptoms shortly after purchase.
Unfortunately, the bird had been allowed to intermingle with the entire
collection of macaws in the new home, violating basic rules of quarantine
procedure. All birds (one Scarlet, two Blue and Golds, one Green Wing, and one
Hyacinth) also developed symptoms and died over a period of 4 - 24 months! These
types of horror stories are not uncommon in avian medical practices. Careful
quarantine procedures and preventative health screening probably can avoid most,
but not all, of these nightmares. Your veterinarian should be able to help you
establish a protocol for new birds which will help protect your existing
collection as well as your new arrivals from infectious diseases such as Macaw
Wasting Disease. In general, the
infectious agent of Proventricular Dilitation Disease is regarded as one of low
morbidity (demonstration of symptoms), but high mortality (death in affected
birds).
Clinical symptoms of Proventricular Dilitation Disease
are fairly well known. Depression, regurgitation, passage of whole seed in the
stool, and diarrhea are commonly seen. Most
affected patients show pronounced weight loss. Secondary bacterial infections
are common. Some individual birds, more commonly African grey parrots and
Cockatoos, may show varying symptoms related to the nervous system.
In those patients, abnormal head movement, incoordination, and rarely,
lameness are seen. An
important observation is that all of these symptoms can be seen in other
disorders. Toxicities, tumors ot the
digestive tract, and foreign material impaction are also possible causes of
similar symptoms and should always be considered. Immune system disorders have
also been forwarded as possible causes of similar symptoms.
It is thought that the infectious agent of Proventricular
Dilitation Disease proceeds to selectively destroy nervous function to the
proventriculus, ventriculus (gizzard), and small intestine in most cases.
Without nervous control, these portions of the digestive system become
flaccid and unable to contract. Secondary infections easily can occur since food
is not moved through at a normal rate. Since destroyed nerves cannot regrow,
there is virtually no chance of return to normal function.
Some treatments have resulted in clinical improvement in selected cases.
It is completely unknown if those individual birds will remain normal, or
if they may have had other conditions that were mimicking this disease.
Accurate diagnosis is both necessary and challenging in these patients.
When a bird has the symptoms described, a physical exam and diagnostic
workup is indicated. There is,
unfortunately, no blood test or other definitive test that is specific for
Proventricular Dilitation Disease. Since the symptoms themselves are not
specific for PDD, other diseases should be ruled out with the current and
appropriate screening tests recommended by your avian veterinarian. Probably the
most valid diagnostic test for Proventricular Dilitation Disease when suspected
in an individual bird with classically recognizable signs is radiography.
Classic dilitation of the proventriculus is highly suggestive. An upper GI
series with barium can be even more informative and may lend more support to the
clinical diagnosis. Crop biopsy has been forwarded as both a diagnostic and
screening test for detection of this disase in suspect birds. At present time,
this disease is defined by suggestive clinical signs in the presence of
supportive histipathology of an afflicted sample site of a patient. All of these
diagnostic tests lend support to a clinical diagnosis of Proventricular
Dilitation Disease by an experienced avian veterinarian. At this point in time,
however, the true and specific diagnosis of Proventricular Dilitation Disease is
only made after death of the patient or biopsy of the diseased tissues involved.
Viewing the likely infectious nature of this disease, sick birds should be
isolated from normal birds. Consult
with your avian veterinarian regarding a specific disinfection program if
indicated.
Outbreaks of small clusters of cases in parrot
collections have been reported. Overall, however, individual or small numbers of
cases seem to be the most commonly encountered in avian medical practice. In
enclosed and indoor collections, dissemination of disease amongst birds seems to
be more common than in those collections with good air quality and ventilation.
Worldwide, the numbers of cases of Proventricular Dilitation Disease in domestic
hand raised parrots seems to be steadily increasing. It is not uncommon to
confirm the presence of this disease in chicks that have been sold unweaned into
the pet bird consuming community or into the pet trade industry. This disease,
therefore, is one of several infectious diseases with potentially very
significant impact on aviculture as well as the pet bird industry. There are
ongoing research efforts, hopefully, progress towards isolation of the virus,
vaccine development, more accurate tests, and potential treatment can be made
SOON, before the disease becomes even more common in our birds.
Information
Provided by:
Brian
L.
Speer
,
DVM, DIP, ABVP, ECAMS
Certified
in Avian Practice
European-Certified
Avian Specialist
The
Medical
Center
For Birds
3807
Main Street
Oakley
,
CA
94561
Phone:
925-625-1878
Fax:
925-625-8511
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