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History
Proventricular Dilatation Disease (PDD, PDS, Macaw Wasting Disease, MWD) is a disease
not only of macaws but of many psittacine species. Cockatoos, conures, eclectus parrots
and many African and Asian species have been infected. A causative agent has recently
been identified and appears to be a virus which is currently being further characterized.
Signs
PDD affects the nerves of the GI tract and results in dilation of the stomach and
lack of normal muscular contractions. The birds then regurgitate, pass undigested
seed in the feces and lose weight. Weanlings fail to wean or revert back to handfeeding
and will have slow crop emptying times. Some birds may have neurologic signs such
as weakness, incoordination and head tremors, in addition to the gastrointestinal
problems. The onset of these signs can be very slow and the symptoms often mimic
those of other diseases. Mortality often approaches 100%.
Diagnosis
Classic signs of weight loss, regurgitation, juvenile behavior and passing undigested
seed in a susceptible species is suggestive of infection. PDD-suspect birds can be
radiographed (X-rayed) to identify a dilated stomach. Oftentimes, laboratory values
will reveal elevated muscle enzymes due to the weight loss and damaged stomach muscles.
The most diagnostic test is stomach biopsy, as evidence of nerve damage may be recognizable
upon microscopic examination of the stomach tissue. This may be obtained by surgery
or by performing a necropsy (autopsy). An alternative crop biopsy has been used in
juveniles demostrating clinical signs but is generally a poor test for an adult bird.
The technique, however, has fewer risks.
Transmission
The transmission of PDD appears to be by the fecal route but other modes may exist.
Treatment
Isolation or euthanasia of affected birds is necessary in order to control an outbreak.
Treatment with antiviral medications has been attempted, but their effectiveness
has not demonstrated any improvement. Preliminary trials of immuno-modulating drugs
and feeding a liquid diet show some promise at improving an infected pet bird's quality
of life. Currently, isolation is the only way to prevent transmission of the disease
to other birds in the household or aviary. Disinfection with bleach, nolvalsan, wavicide
and virkon-s is recommended and may help reduce the possibility of transmission.
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