Heavy Metal Poisoning (Lead and Zinc)
Description: Zinc and lead poisoning are probably the most common types of poisoning found in pet birds. The ingestion of these toxins that poison birds may also be known as New Wire Disease which usually occurs in curious, inquisitive birds that tend to chew on their cages or destroy toys, which results in the ingestion of some of the materials. All birds are susceptible to heavy metal toxicosis if exposed to the toxins. Galvanized cage wire has both lead and zinc in the welds and the white, powdery substance found on new wire also contains these heavy metals. Certain cage clips also contain zinc. Some plastic toys contain zinc which can leach out if pieces are ingested. Adhesives can also contain zinc. Galvanized dishes and containers are other sources of zinc contamination, and pennies minted in the United States since 1982 contain 96-98% zinc coated with copper. Lead poisoning is also called plumbism, from the scientific periodic table abbreviation for lead (Pb).
Lead exposure may occur through the inhalation of fumes from lead-containing gasoline. Some candles have a wick that contains lead and other metals to stiffen the wick, and when burned, this can release lead and other toxins into the air.
Diagnosing zinc or lead poisoning first includes a review of the bird’s surroundings, including the cage, toys and other equipment directly around them. Anything the bird may come in contact with outside of the cage must also be evaluated in case that any of the objects contain the metals. Home lead test kits are available that can be used to detect lead in environmental samples. Commercial laboratories can also be utilized to detect lead in samples.
Once ingested, lead may have already been dissolved in the bird’s GI tract and dispersed to other tissues; therefore they may not show in a radiograph (x-ray). With zinc, this element will not become deposited into tissues, so removing the source of the zinc will eliminate the poisoning symptoms, often without chelation therapy (but if the bird is showing clinical signs of zinc toxicosis, chelation should be instituted as soon as possible).
Clinical signs of lead toxicosis include: lethargy, depression, decreased appetite, chronic weight loss, weakness (such as droopy wings), diarrhea, regurgitation, increased urination, ataxia, anemia, blindness, circling, head tremors, head tilt, seizures or death. Amazons suffering from lead toxicosis may demonstrate blood or hemoglobin (the red pigment from ruptured red blood cells) in their urine, as many other species, including African Grey parrots.
Zinc toxicosis also targets the kidneys and signs of these problems include: increased urination, increased water consumption, GI problems, depression, weight loss, diarrhea, high blood sugar, bluish mucous membranes, seizures, lack of coordination and death.
The symptoms a bird shows will depend on the amount of zinc or lead the bird has been exposed to and for how long. A bird can have acute or chronic metal poisoning. Acute intoxication occurs when the bird is exposed to a large amount of zinc or lead at one time and chronic intoxication occurs when the bird is exposed to small amounts over a longer period of time. Lead can dissolve from the GI tract and become deposited into bone and other tissues, rendering it invisible on radiographs.
Immediate Care: If heavy metal toxicosis is suspected, it might be necessary to begin treatment before the clinical test results are back from the lab. It is possible to run tests to quantitate the levels of both lead and zinc in the bloodstream of birds; however the amount of whole blood necessary to run each test is prohibitive for the smaller birds. Chelation therapy is used to remove lead and zinc that is circulating in the bird’s bloodstream. Chelation agents, such as CaEDTA (calcium disodium ethylene diamine tetracetate) and calcium disodium versenate, are used to treat birds poisoned by zinc or lead. These agents are administered as injections to the pectoral muscles twice daily for 10 days. The agents can cause kidney and GI problems and should be used for the shortest amount of time necessary to affect a cure. Usually chelation is administered for ten days, with injections being given 2-3 times per day.
For both lead and zinc poisoning the oral chelation agent DMSA (dimercaptosuccinic acid) is the preferred treatment and can be used in conjunction with CaEDTA.
Long Term Care: If a bird develops increased urination or water consumption, or has protein or blood in the urine while receiving the chelation agents, the treatment may need to be discontinued and restarted after the bird is stabilized.
An avian veterinarian may administer certain cathartics by gavage tube to help expedite the removal of any metal particles from the gastro-intestinal tract. Often, peanut butter, psyllium, mineral oil, corn oil or barium sulfate may be given to help objects pass out of the GI tract. In some cases, the toxic material can be flushed out of the crop or ventriculus (grinding stomach) under anesthesia using specialized equipment. If a piece of wire containing lead or zinc, for example, has perforated or penetrated into a portion of the GI tract, surgery or an endoscopic procedure might be necessary to remove the offending object.
In addition to chelation therapy, support care is also necessary. Any bird with signs of dehydration or polyuria/polydipsia (increased urination and water consumption) will benefit from fluid therapy. Antibiotics or antifungals may be necessary to treat secondary infections. Since lead may result in anemia, often iron dextran and vitamin B complex are administered to help the bird’s body replace red blood cells. Nutritional support may be necessary if the bird is not eating or not taking in enough calories to maintain adequate body weight. It is also a good idea to provide adequate heat and humidity for a bird in a weakened state from heavy metal toxicosis.
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