Abstract

The San Diego Zoo parma wallaby collection has had a 19.2% prevalence (23/119 animals) of megaesophagus over the last 25 years. A retrospective review included 23 necropsy records and 61 clinical records. Records were reviewed for evidence of megaesophagus including regurgitation, swelling in the cervical region, weight loss and dilation of the esophagus on radiographs or necropsy along with histopathologic findings. A prospective study included eight animals in the current collection that were immobilized for routine exam, CBC/chemistry, acetylcholine titer, lead levels, toxoplasmosis titers, mineral panels, and contrast esophagrams. To determine the prevalence of megaesophagus amongst other institutions, a survey was sent out to 30 zoos. The retrospective study did not identify a cause but did elucidate presenting clinical signs for affected animals and that clinical signs are not seen until the disease is advanced. Necropsies ruled out vascular anomaly as a cause. The prospective study revealed megaesophagus and severely delayed esophageal transit time in all eight animals examined. Myasthenia gravis, lead, toxoplasmosis and thyroid disease were ruled out as possible causes. One other institution reported a single case of megaesophagus which is currently under treatment. In conclusion, myasthenia gravis, lead toxicity, hypothyroidism, toxoplasmosis and vascular ring anomaly have been discounted as possible causes of disease in our parma wallaby collection. Parma wallabies often have no clinical signs until severe and chronic dilation of the esophagus is present.