History

A 2-year-old 0.7-kg (1.5-lb) blue and gold macaw (Ara ararauna) was examined because of hyporexia, lethargy, and chronic weight loss. On physical examination, the macaw had a body condition score of 2/9 and was mildly dehydrated (< 5%). Results of a CBC and plasma biochemical analyses indicated lymphocytic leukocytosis (WBC count, 20.1 × 10³ WBCs/dL [reference range, 10 × 10³ to 20 × 10³ WBCs/dL]; and lymphocyte count, 11.1 × 10³ lymphocytes/dL [reference range, 3.50 × 10³ to 8.06 × 10³ lymphocytes/dL]) and hyperuricemia (uric acid concentration, 15.7 mg/dL [reference range, 2.9 to 10.6 mg/dL]). There was no evidence of hemoconcentration (PCV, 48% [reference range, 42% to 56%]¹). Results for cytologic examinations with Gram staining of a fecal smear and a crop wash sample were considered clinically normal. The macaw was treated with an isotonic solution^a of balanced electrolytes in sterile water (50 mL/kg [23 mL/lb], SC, once), enrofloxacin (15.0 mg/kg [6.8 mg/lb], PO, q 12 h for 14 days), and a probiotic^b (0.5 g, PO, q 12 h for 14 days). The owners were instructed to monitor the bird's weight and to return the macaw for a recheck examination in 2 weeks, or sooner if issues arose or the bird's body weight decreased > 7% (0.05 kg [0.11 lb]).

Two weeks later, the macaw was returned for reevaluation. The macaw was anorexic, weak, and mildly dehydrated (< 5%), and its body weight had decreased to 0.62 kg (1.36 lb). The owners declined bloodwork but approved general anesthesia for radiography (Figure 1).

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Right lateral (A) and ventrodorsal (B) whole-body radiographic images of an anesthetized 2-year-old 0.62-kg (1.36-lb) blue and gold macaw (Ara ararauna) evaluated for anorexia, lethargy, and chronic weight loss.

Citation: Journal of the American Veterinary Medical Association 257, 8; 10.2460/javma.257.8.801

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Formulate differential diagnoses and treatment strategies from the history, clinical findings, and Figure 1—then turn the page →

Radiographic Findings and Interpretation

A large (approx 6.5 × 3.5 × 2.8-cm), ovoid, gasfilled structure spanned from dorsal of the caudal aspect of the cardiac silhouette to the level of the mid region of the synsacrum, with most of the gas-filled portion of the structure left of midline (Figure 2). The macaw's low body condition score was radiographically evident with less than a normal amount of fat and soft tissue on the dorsal aspect of the neck, decreased opacity in the area of the pectoral muscles, and a concaved caudoventral coelomic wall margin. In addition, the cardiac silhouette was undersized. The remaining structures were radiographically normal.

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Same radiographic images as in Figure 1. A large (approx 6.5 × 3.5 × 2.8-cm), ovoid, gas-filled structure (arrows; A and B) extends from the mid to the caudal regions of the coelomic cavity. The macaw's low body condition score is radiographically evident, with little soft tissue evident along the dorsal aspect of the neck (white asterisk; A) and in the area of the pectoral muscles (black asterisks; A) and with concavity of the caudoventral coelomic wall margin (arrowheads; A). The cardiac silhouette (cross; A and B) is abnormally small.

Citation: Journal of the American Veterinary Medical Association 257, 8; 10.2460/javma.257.8.801

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The gas-filled structure was consistent with a proventriculus dilated with gas. Given the species, clinical signs, and radiographic findings, the primary differential diagnosis was proventricular dilatation disease with secondary emaciation and dehydration. The radiographic appearance of microcardia could have been caused by dehydration, emaciation, or both.

Treatment and Outcome

A crop biopsy was performed while the macaw was anesthetized, then the macaw was recovered from anesthesia without complications. The macaw was hospitalized and treated with an isotonic solution of balanced electrolytes in sterile water (60 mL, SC, q 24 h), enrofloxacin (10.0 mg/kg [4.5 mg/lb], IM, q 12 h), and meloxicam (1.0 mg/kg [0.5 mg/lb], IM, q 12 h). Results were negative for a bornavirus PCR assay performed on a fecal swab sample and a blood sample submitted to the University of Georgia Infectious Disease Laboratory; however, results of histologic examination of crop biopsy samples indicated severe lymphohistiocytic ganglionitis and myositis, consistent with proventricular dilatation disease. Because of the grave prognosis, the owners elected euthanasia for the macaw. Necropsy was performed by the University of Georgia Infectious Diseases Laboratory, and results of a reverse transcription PCR assay performed on brain tissue were positive for bornavirus; however, the virus was not detected in any other tissue.

Comments

Proventricular dilatation disease or avian ganglioneuritis has been associated with avian bornavirus and is a fatal infectious disease of birds. The most common signs are abnormal CNS or gastrointestinal signs leading to chronic weight loss, regurgitation, delayed crop emptying, and undigested food passed in the feces; however, sudden death from myocarditis and arrhythmias has also been reported.² These signs are largely a result of immune-mediated inflammatory damage to the autonomic nervous system, particularly to the vagus nerve, disrupting normal peristalsis and processing of food. An important clinical feature is the dilation and atony of the gastrointestinal tract, especially the proventriculus, such as was suspected on the basis of radiographic findings for the macaw of the present report. Encephalitis may also occur, and CNS signs previously reported include affected birds falling off their perches, ataxia, seizures, blindness, and signs of depression.^2,3 Avian bornavirus is, so far, the only known etiologic agent for this disease.²

A presumptive antemortem diagnosis of proventricular dilatation disease is based on suggestive findings in the patient's history and results of physical and radiographic examinations combined with detection of avian bornavirus on PCR assay. A definitive diagnosis of proventricular dilatation disease is based on the characteristic histopathologic finding of lymphoplasmacytic ganglioneuritis in any tissue, but especially tissues of the upper gastrointestinal tract.² Radiography is used as a guide, not only to identify abnormalities in the gastrointestinal tract, but also as a screening test because of vague clinical signs of affected birds. Radiographic evidence of dilation of the proventriculus, as seen in the macaw of the present report, is indicative of a disease of the gastrointestinal tract, with proventricular dilatation disease being the top differential diagnosis.² Other causes of proventricular dilation include parasitism, candidiasis, macrorhabdosis, mycobacteriosis, foreign body, neoplasia, and heavy metal toxicoses.² In birds for which subjective assessment for radiographic evidence of proventriculus dilation is equivocal, the proventricular diameter-to-maximum dorsoventral keel height ratio could be assessed because results > 0.52 (reference limit, < 0.48) indicate dilation of the proventriculus; however, there is no correlation between the magnitude of the ratio and short-term survival time.⁴ For the macaw of the present report, the proventricular diameter-to-maximum dorsoventral keel height ratio was 0.78, and dilation of the proventriculus with gas was an atypical finding, compared with soft tissue or fluid dilation that is usually seen with proventricular dilatation disease.⁵ Other portions of the gastrointestinal tract (eg, crop, ventriculus, and small intestines) may also be distended; however, none are specific for proventricular dilatation disease, and the degree of distention radiographically evident varies.^2,4 Positive-contrast radiography of the upper gastrointestinal tract may be performed in birds with otherwise unclear findings and facilitates determining gastrointestinal luminal size and position and monitoring gastrointestinal transit time; however, increased transit time is not specific or sensitive for proventricular dilatation disease.^2,5

Detection of avian bornavirus relies on the amplification of the viral genome with a reverse transcription PCR assay, serologic assays for detection of antibodies against the virus, or identification of histopathologic findings characteristic of an infection with the virus. As was the case in the macaw of the present report, false-negative results for bornavirus PCR assays performed on blood or fecal samples may occur. Conversely, detection of bornavirus by PCR assay on blood or feces may occur in birds without clinical disease. Further, an indirect fluorescent antibody assay and Western blot assay can identify exposure to bornavirus but cannot determine whether exposed birds are clinically affected or otherwise healthy.^2,3 Histologic examination, ideally of crop biopsy samples, is currently the diagnostic test of choice for diagnosis of proventricular dilatation disease.⁶ Unfortunately, histologic examination can also lack sensitivity because not all ganglia in the sampled area will be affected.^2,3,5 A study⁷ shows that 22 of 29 (76%) birds with clinical proventricular dilatation disease had lymphoplasmacytic ganglioneuritis identified on histologic examination of crop biopsy samples that included a blood vessel and nerve. Although more proventricular or ventricular tissue, compared with crop tissue, may be affected, these structures are not typically biopsied because of higher risk for subsequent perforation and death.⁷ Usually, all of these antemortem diagnostic procedures are used in conjunction to accurately diagnose proventricular dilatation disease. Clinical signs of proventricular dilatation disease and associated inflammation may be eased by administration of NSAIDs; however, life expectancy of affected birds cannot be predicted.^3,5

Results for the macaw of the present report highlighted the importance of radiography in birds with nonspecific clinical signs, such as weight loss. Proventricular dilatation disease can be difficult to diagnose, and results of radiographic examination of this macaw helped us prioritize the disease as the primary differential diagnosis.