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| Ongoing Investigation
into Proventricular Dilation Disease at the Ontario Veterinary College
Michael Taylor DVM and Bruce Hunter DVM MSc
Ontario Veterinary College, University Of Guelph, Guelph, Ontario
Proventricular dilation disease (PDD) is an infectious disease of several orders of birds. It has been known to occur in imported parrots since the late 1970's. Over the past five to six years PDD has been more frequently diagnosed at laboratories throughout North America and Europe. This rise in occurrence comes at a time when importation of wild caught birds has all but ceased. PDD outbreaks can be devastating, especially in indoor aviaries.
A virus has been found in the feces of affected birds but awaits further identification. The virus causes damage to the autonomic nervous system of the host. The myenteric portion of the autonomic system is most severely affected leading to abnormalities in the control of gastrointestinal motility. Digestion is impaired with the consequence that classically infected birds lose body condition before finally starving to death. The current "gold standard" for the positive diagnosis of PDD is the finding of lymphoplasmocytic infiltrates in ganglia and associated nerve fibers of the myenteric plexus of the gastrointestinal tract.
Early detection of PDD has been difficult to impossible. The objective of our study was to examine techniques that might allow early detection of this disease so that infected individuals could be removed from the flock preventing further new cases of the disease. As well we had proposed that certain carrier or chronically infected birds were likely to be present in an exposed population acting as reservoirs of the virus. Were these birds the source for new infections? Could these birds be detected? For the past two years we have endeavoured to answer these and other questions about PDD.
Components of the Study
Biochemical: All birds screened in the study had a twelve element biochemical profile performed.
Hematological: Complete blood counts were performed using the phloxine stain method.
Crop biopsy: The safest, most accessible portion of the myenteric nervous system is in the wall of the crop and so this site has been recommended as the best site for biopsy. A sample of the crop wall approximately 0.7 cm X 0.7 cm was collected from birds via a ventral midline approach and placed immediately in 10% neutral buffered formalin. The crop wall and the skin were closed with 5-0 PDS suture. The specimens were sectioned routinely, stained with Hematoxylin and Eosin and examined with a light microscope.
Fluoroscopic: Birds with suspicious historical, clinical, biochemical or crop biopsy findings were examined using a Phillips Medical fluoroscope at the Ontario Veterinary College. Barium sulfate was administered by gavage tube as a contrast agent at a rate of 1.5 ml for each 100 grams of body weight. Lateral and dorso-ventral examinations were performed routinely at 15, 30 and 45 minutes. Approximately five minutes of SVHS videotape was recorded at each time period. In some abnormal birds, further examinations were necessary at 60 or 120 minutes post barium administration. Crop, esophageal, proventricular, ventricular and duodenal motility were examined for each bird. Videotaped examinations were digitized for further analysis using an area measurement computer program so that accurate measurements of organ size could be made.
Histologic: All birds dying of suspected PDD in an aviary with endemic disease received a complete post mortem examination with examination of all tissues. This is the first time that this form of systematic examination has been carried out in PDD infected birds.
Electron Microscopy of Feces: We have begun to look at suspect "chronically infected" birds' feces to identify the presence of virus particles.
The Findings So Far
Fluoroscopic and Histologic: We have demonstrated the utility of barium contrast fluoroscopy as a technique to examine the abnormal motility of the psittacine gastrointestinal system. Dzuik and Duke first described the normal motility of the turkey ventriculus. We described, for the first time, the use of modern video fluoroscopy in the macaw and found very similar motility patterns to those described for the turkey ventriculus. Avian pathologists have suggested from routine histopathogic studies that PDD appears to affect the gastrointestinal tract in a random, segmental fashion. This was confirmed in this study for the first time, both fluoroscopically and histologically. Involvement of the crop, esophagus, proventriculus, ventriculus and duodenum in all possible combinations was recorded. The most commonly observed lesions were dilation of the ventriculus, duodenum and proventriculus. Crop dilation was especially common in African Grey Parrots. Distal esophageal (post ingluvial) dilation was a rarer finding in all species but did occasionally occur. Ventricular motility was also assayed and found to be a good early indicator of PDD. The psittacine ventriculus has a vigorous pattern of motility that is grossly similar to the turkey. Birds suffering from PDD evidence changes in the coordination and effectiveness of these contractions at an early stage of the infection. Death was most frequently associated with advanced ventricular and/or duodenal motility problems. Fluoroscopic lesions were compared to crop biopsy and/or necropsy findings. A important finding from the fluoroscopic study was the detection, for the first time, of naturally occurring, chronically infected parrots. We currently have several chronically infected birds in isolation who have been living with PDD for over two years. While the initial findings are very exciting, further research is required to improve our ability to detect these chronically infected birds more easily. We now believe that it is the chronically infected parrot who poses the greatest risk to aviary health.