HEAVY METAL TOXICITY IN PSITTACINE BIRDS
Aizenberg I.1 Miara L.2 and Ulman O.2
1. Hebrew University of Jerusalem, School of Veterinary Medicine
2. 'Kol-Hay' Veterinary Clinic, Rehovot
Heavy metal toxicities are of major concern in wild and captive avian species. In wild birds it is impossible to fully control heavy metal toxicity, nevertheless it is our responsibility to prevent it in captive species. Of the heavy metals, lead and zinc are the most important in captive birds since they are common in their immediate environment. Clinical signs of lead and zinc toxicity (LZT) are very similar but are not specific since many disease conditions can show the same signs. Therefore a thorough history should be taken followed by a physical examination, radiographs, blood tests and blood and plasma levels of lead and zinc. Specific treatment is indicated with a good prognosis according to the severity of the poisoning.
A case of zinc toxicity in a pair of Cacatua Alba (White Cockatoo) will be discussed.
Metal toxicosis is a major problem affecting both wild and captive avian populations (1,2,3,4). Historically, toxicities involving lead, zinc, iron, or copper appear to have the greatest clinical impact on birds. For example, lead and zinc toxicities are commonly recognized causes of illness in pet psittacine birds, birds in zoological collections, and waterfowl (2,5,6,7). Lead toxicosis due to ingestion of lead shot is claimed to be the cause of death of more than 1.6—2.4 million ducks annually. (8)
Parrots are known as very curious and active creatures who like to chew anything in their environment. Since there are many objects in their immediate environment which contain zinc and almost as many that contain lead they are prone to LZT. (5,6)
Objects that contain zinc are galvanized cages, food and water dishes, toys, jewelry, chains etc. Objects that contain lead include batteries, curtain weights, PVC, toys etc. Clinical signs of LZT are regurgitation, diarrhea, anorexia polydipsia and polyuria, dyspnea, depression, weakness, ataxia, seizures, weight loss and death. (9) The final diagnosis is made by measuring the levels of lead and zinc in the blood. Normal blood lead levels are considered to be less than 0.2ppm, and normal plasma zinc levels are less than 2ppm. (9) Radiography is a useful method for imaging metallic objects in the gastrointestinal tract. Endoscopy can aid in finding metallic objects in the ventriculus as well as for extracting them. Complete blood count (CBC) may show heterocytosis, and anemia. Blood chemistry can show dehydration and elevated uric-acid levels. Treatment includes supportive care, the use of specific chelating agents and bulking and cathartics. Chelating agents used are Ca-EDTA (calcium disodium ethylene diamine tetraacetic acid), DMSA (Dimercaptosuccinic acid) and D-Penicillamine. (9)
A pair of 2.5 year old white cockatoos was presented with clinical signs of depression, regurgitation, diarrhea, dyspnea and weakness. The male was more affected than the female. Both were housed in a galvanized mesh cage locked by a galvanized lock. Radiographs revealed small metallic objects in both parrots. The only abnormality in the blood tests was mildly elevated uric acid (11.3mg/dl, normal: 3.5-9.3).
Fecal examination did not reveal any pathological finding. Chlamidial IFA was negative. Plasma zinc level of the male was above 3ppm (there was not enough plasma from the female to meet the laboratory requirement). A final diagnosis of zinc toxicity was made. Initial treatment included parenteral fluids (lactated Ringer), oral D-penicillamine (25 mg bid for 5 days), and intramuscular Ca-EDTA (35 mg bid for 5 days). The birds also got psyllium and metoclopramid (Pramin) before each meal. Both cockatoos showed a marked improvement after 2 days. No radiograph follow-up or plasma zinc levels were done since the parrots were fully recovered according to the owner.
Heavy metal toxicities are more common than it seems. Since the environment of the captive birds is full of material made from zinc and lead we must investigate for LZT in addition to other diseases. (2,3,5,6) Clinical signs of LZT are not pathognomonic but are common to many other conditions, therefore LZT should always be a differential diagnosis. A thorough history is probably the most important step in the diagnosis. Radiography, plasma zinc levels and blood lead levels can lead to a final diagnosis. CBC and blood chemistry might support the diagnosis. A correct diagnosis will lead to the appropriate treatment and will improve the prognosis. Misdiagnosis will probably lead to the death of the bird.
An important part of the treatment is the prevention of reoccurring toxicities. Owners should be advised about the risk of hazardous materials in the birds' environment.
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