Zinc Toxicosis in Hispaniolan Amazon Parrots (Amazona ventralis)
Susan E. Little and Anne Smith
Department of Medical Microbiology and Parasitology, College of Veterinary Medicine, The University of Georgia, Athens, Georgia 30602 USA (Little) and Department of Natural and Environmental Resources, Rio Abajo Aviary, PO Box 439, Arecibo, Puerto Rico 00613 (Smith)
Abstract. In late summer of 1996, several Hispaniolan Amazon Parrots in an aviary collection in Puerto Rico developed weakness, lethargy, and vomiting. Over a four week period, four birds died and were submitted to the Southeastern Cooperative Wildlife Disease Study (Athens, Georgia, USA) for necropsy. Moderate to pronounced hemosiderin deposition was present in the hepatic parenchymal cells, renal tubular epithelium, and intestinal epithelial cells. Liver zinc levels ranged from 93 to 216 ppm. The presence of severe hemosiderin deposition as the predominant histologic finding in these birds underscores the extent of hemolysis associated with zinc toxicity. In addition, these cases illustrate that a history of exposure to zinc containing materials, together with histologic evidence of severe hemolysis, indicate zinc toxicosis should be considered as a diagnosis.
Key Words: Amazona ventralis, Avian, Hemosiderosis, Hispaniolan Amazon parrot, Zinc toxicosis
Introduction
Zinc toxicosis occurs in caged birds following ingestion of zinc from the environment, usually from caging material. 1 Clinical signs of zinc toxicosis in birds include weakness, polyuria, polydipsia, vomiting, and weight loss. 2 Limiting the extent of morbidity and mortality due to zinc toxicosis in an aviary is dependent upon accurate, timely diagnosis of the condition and rapid identification and removal of the source of zinc to the birds. Definitive diagnosis requires submitting appropriate tissue to a toxicology laboratory for heavy metal analysis and comparing levels with those of appropriate control animals.
In 1990 zinc toxicosis was diagnosed in a mortality event involving several Hispaniolan Amazon Parrots (Amazona ventralis) held in flight cages at the Rio Abajo aviary in Puerto Rico. Birds were obtaining zinc by consuming precipitate which formed on the galvanized wire caging material. 1 A change in management practices to include routine stringent washing of the cage material to remove excess zinc prevented further mortalities; however, in 1994 several birds in flight cages again developed weakness, lethargy, vomiting, and diarrhea. Four of these birds were submitted to the Southeastern Cooperative Wildlife Disease Study for necropsy.
A gross necropsy examination was performed on each of the birds. Sections of brain, kidney, skeletal muscle, liver, spleen, crop, proventriculus, ventriculus, intestine, heart, gonad, lung, and air sac were fixed in 10% neutral buffered formalin, embedded in paraffin, sectioned at 3 µm thickness, and stained with hematoxylin and eosin. Replicate sections of each tissue were stained with Perls' iron stain. 3 Samples of liver were submitted to either the Athens Diagnostic Laboratory (Athens, Georgia, USA), the UGA Soil Testing and Plant Analysis Laboratory (Athens, Georgia, USA), or the Tifton Veterinary Diagnostic Laboratory (Tifton, Georgia, USA) for determination of zinc levels according to standard techniques.
At gross examination, one of the four birds had renal urate deposition and another had a focal ulcerative lesion in the ventriculus. Radiographs of the carcasses did not reveal any radiodensities consistent with ingested metallic objects. No substances other than food material were found on close examination of the gastrointestinal contents. Histologic examination of tissues from all of the birds revealed diffuse, moderate to pronounced deposition of a golden brown pigment interpreted to be hemosiderin throughout the hepatic parenchyma. In most areas the cells were distended and the cytoplasm heavily laden with hemosiderin (Fig. 1).
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| Figure 1. Hispaniolian Amazon Parrot, Liver, H&E stain. Notice golden-brown hemosiderin deposition in hepatic parenchyma of bird with zinc toxicosis. Size bar = 24 µm. |
Hemosiderin was also present in renal tubular and intestinal epithelial cells. Perls' iron stain of all affected tissues resulted in deep blue staining of the hemosiderin (Fig.2).
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| Figure 2. Hispaniolian Amazon Parrot, Liver, Perls' iron stain. Hemosiderin deposits in hepatic parenchymal cells stain blue. Size bar = 24 µ. |
Liver zinc levels were determined for each of the four birds and ranged from 93 ppm to 219 ppm. Lead was not detected in the liver of three of the birds; lead testing was not performed for the fourth bird.
While severe hemolysis can occur in a number of diseases, zinc toxicosis should be considered in animals with hemolytic anemia or profound tissue hemosiderin deposition and a history of access to a zinc source. 4,5 Confirmation of elevated tissue zinc levels are required before reaching a definitive diagnosis. However, not all diagnostic laboratories can support the rapid response needed in ongoing mortality events. When test results are delayed, characteristic histologic lesions indicating a severe hemolytic crisis together with a history that includes the use of new cages or previous problems with zinc toxicosis in the aviary may allow a preliminary diagnosis of zinc toxicosis. This preliminary diagnosis can allow for short-term management changes to prevent the loss of additional birds while awaiting metal testing results.
Common sources of zinc to animals include cage material such as galvanized wire or cage bolts on pet carriers and pennies minted after 1982. 1,5 Some food dishes and small toys also contain high levels of zinc. 6,7 In cases where these objects are found in the gastrointestinal tract by radiographic or endoscopic examination or at necropsy, diagnosis of zinc toxicity is straightforward. However, animals may also obtain excessive levels of zinc by consuming the white precipitate that forms on or around zinc-based caging material. 8 For this reason, washing of the wire with an acidic solution to remove the precipitate is recommended. Washing of caging will reduce but not eliminate the problems associated with zinc toxicosis. 9
This aviary had experienced mortality due to zinc toxicosis in the past which was attributed to consumption of zinc precipitate from flight cage wire. A program to routinely wash precipitate from the cages was instituted and prevented additional cases of zinc toxicosis for four years. The affected birds described here apparently were drinking zinc-laden water dripping from the cage wire. Removal of the birds from the flight cages and increasing the frequency of cage washing ameliorated the problem, and no new clinically evident zinc toxicosis cases have been recognized at this aviary. Serum zinc levels of birds housed in flight cages were monitored 2 months following this mortality event and ranged from 4.7 ppm to 9.3 ppm zinc, levels considered to be elevated. 1
Acknowledgments
This work was supported through sponsorship from the fish and wildlife agencies of Alabama, Arkansas, Florida, Georgia, Kansas, Kentucky, Louisiana, Maryland, Mississippi, Missouri, North Carolina, Puerto Rico, South Carolina, Tennessee, Virginia, and West Virginia. Funds were provided by the Federal Aid to Wildlife Restoration Act (50 Stat. 917) and through Grant Agreement 14-45-0009-94-906, National Biological Service, U.S. Department of the Interior.
References
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