By Margaret A. Wissman, DVM, DABVP, Avian Practice
Photo Courtesy Lori Welbourne, Canada
Heavy metal toxicosis is a common type of poisoning found in pet birds.
Zoe, a peach-faced lovebird, was quite ill. She was losing weight, drinking too much water and concurrently urinating excessively; she was weak and just not her busy, inquisitive self.
The owner just had built an outdoor summer cage so Zoe could enjoy the fresh air and sunshine. Unfortunately, the cage was constructed of hardware cloth, which can have lead and zinc in the welds. When I asked, the owners confirmed that, sure enough, there was a light coating of a white powder on the wire. And Zoe, being a lovebird and prone to chewing, had been exploring the new cage and chewing on the wire, eventually ingesting enough lead and zinc to make her very ill. There is actually a name for this: New Wire Disease.
Poisoning from lead and zinc, technically known as heavy metal toxicosis, is probably the most common type of poisoning found in pet birds. There are many sources of lead and zinc that a bird may become exposed to and then ingest. Galvanized wire, clips and chains may all contain lead and/or zinc. Some galvanized coatings contain 99.9-percent zinc while others are 98-percent zinc and 1-percent lead.
Zinc is also present in many items found around the house, including some adhesives and some plastic items that may leech out zinc (which won’t show up on radiographs). In the U.S. today, all paint sold is lead-free. However, lead may be present in toxic levels in the drying agents. So, unless the paint label states “lead free,” lead should still be a consideration.
Lead and zinc toxicosis are more commonly encountered in inquisitive birds, birds that tend to chew on the cage and birds that and destroy toys, resulting in the ingestion of pieces. But any bird is susceptible to poisoning by heavy metals.
Diagnosing heavy metal toxicosis requires a thorough investigation of the bird’s environment. The cage, toys and cage equipment need to be examined for evidence of toxic materials. If a bird is allowed out of the cage unsupervised, then it may take some super sleuthing to uncover potential sources of toxins around the home.
Because metals show up on radiographs (X-rays), one would think that diagnosing heavy metal toxicosis would be as simple as evaluating radiographs, looking for suspicious little flecks of metal in the gastrointestinal tract. Unfortunately, it isn’t always that simple. This is because, after time, lead may be dissolved completely from the GI tract, where it was initially lodged and instead become deposited in other tissues, such as bone. It may cause GI signs, nervous system signs, renal signs, and it may cause bone marrow problems.
Diagnosis is based on the history, examination of the cage, toys and equipment, radiographs, CBC (complete blood count), plasma chemistry analysis and any other tests deemed necessary. There are specific blood tests for lead and zinc. However, the volume of blood necessary for the test may be prohibitive in the smaller birds, as approximately 0.5 milliliters of whole blood is needed for each test. As a general rule, one can take approximately 1.0 milliliters per 100 grams of healthy bird weight. So with smaller birds, it might be necessary to make a choice and to run only one blood test for lead or zinc. With little birds, blood testing might not be possible due to the small volume of blood that can be safely withdrawn.
Anemia, usually low-grade, is often a clue in diagnosing chronic lead toxicosis. There may be signs of the body trying to make new red blood cells, called regenerative anemia.
If lead or zinc poisoning is suspected, it might be necessary to begin treatment prior to receiving test results. If the history or initial bloodwork supports a heavy metal toxicosis diagnosis, time is of the essence to minimize damage to the internal organs.
Support care, which might include fluid therapy, antibiotics or antifungals to treat any secondary infections present, heat and humidity, an iron injection, vitamin B complex injections and nutritional support, is vital in cases of heavy metal toxicosis. Lead-induced seizures can be controlled with anticonvulsants. Support care can include an oral nutritional supplement called DMG, which can help with seizures by increasing the threshold for seizures, and may help with detoxification as well.
Treatment is called chelation therapy, which is designed to remove lead or zinc circulating in the bloodstream. Calcium disodium ethylene diamine tetracetate (CaEDTA) or calcium disodium versenate are commonly used as chelation agents. Given as an injection, it is usually administered twice daily for 10 days, into the pectoral muscles. It can cause kidney damage and GI problems, so it should be administered for the least amount of time necessary to resolve the intoxication. If increased urination or increased water consumption occur, or if protein or blood is found in the urine, it might be necessary to discontinue the medication for five to seven days, and then therapy can be reinstituted once the patient has stabilized.
D-penicillamine (PA) is an effective chelator for lead, and it can be administered orally. In some cases, both CaEDTA and PA may be administered together until a bird is asymptomatic, and then PA may be used alone until the clinical signs are resolved. Dimercaprol (BAL) is the best agent for removing lead from the central nervous system. It is rarely used, however, because it can be highly toxic if not precisely dosed. DMSA (dimercaptosuccinic acid) is the preferred oral chelator for both lead and zinc poisoning and may be used in conjunction with CaEDTA.
In addition to chelation therapy, oral cathartics may be useful in removing particles containing lead or zinc from the GI tract. Mineral oil, peanut butter, barium sulfate, psyllium, sodium sulfate or corn oil have been used, usually as a slurry that can be gavaged into the crop, and may be repeated until toxic pieces are gone from the gut. Diarrhea will usually result from the administration of any of these items. Activated charcoal may be administered to bind small particles of lead from the GI tract; however, activated charcoal will be inactivated by the concurrent administration of mineral oil.
In some cases, surgery may be required to extract metal pieces embedded in the wall of a portion of the gastrointestinal tract. Endoscopy can be a useful tool for removing heavy metal particles from the GI tract, as well. In some cases, an anesthetized bird may have heavy metal fragments flushed out of the GI tract by tilting the bird at a 45-degree angle, head down, and then pumping warmed saline into the ventriculus to mechanically flush out any toxic particles.
With heavy metal toxicosis, the disease may be characterized as either acute or chronic. The toxin may be ingested as one large dose, or it may be ingested a little bit at a time until a toxic level is reached. The presence and severity of clinical signs often depend on the amount of toxin ingested, the surface area of the particles and length of time that the particles remain in the GI tract.
Clinical signs of heavy metal toxicosis can be vague and may require a thorough history and work-up in order to correctly diagnose the problem. If organ damage is not severe, it can often be reversible, and a pet bird suffering from heavy metal toxicosis can return to excellent health. Early diagnosis and treatment offers the avian patient the best chance for total recovery.