Definition of Lead Poisoning in Dogs
Lead is one of the most basic chemical elements. It has atomic number 82, atomic weight 207.19 and goes by the symbol Pb. Dogs can be poisoned when they ingest lead – especially if they have repeated exposure to the substance. Lead is found in a number of places and in a number of different things, including insecticides, paint, golf balls, newspapers, linoleum, grease, lead weights, lead shot, oil, batteries, fishing sinkers and other household objects. Toxic levels of lead affect a dog’s central nervous system and digestive tract. The signs of lead poisoning can come on slowly or suddenly and primarily include abdominal pain, vomiting, diarrhea and seizures. Many dogs that are poisoned by lead become depressed and wander around aimlessly. They can also become blind and develop dark, chalky diarrhea. Lead poisoning is fairly common in companion dogs in the United States, especially those living in urban settings because of the frequency of lead in the environment, often from older paint. Lead-based paint apparently tastes sweet and is increasingly attractive to dogs as it weathers.
Causes of Lead Poisoning in Dogs – Biological Progression
Lead poses a serious health hazard to dogs and to people worldwide. Dogs get lead poisoning by licking or eating something that contains lead. While lead intoxication affects a number of different bodily systems, in dogs it targets the central nervous system and gastrointestinal tract. Lead poisoning can occur suddenly (acutely) or gradually (chronically), depending on the amount and duration of the dog’s exposure to the toxin. Lead is particularly dangerous because it has the ability to substitute for other substances, such as calcium and zinc, and bind to cells (especially red blood cells) and tissue in their place. When lead competes with calcium, it often settles inside a dog’s bones, where it is stored and can be mobilized at a later time. This adversely affects nerve and muscle transmission. Lead that is absorbed through the gastrointestinal tract enters the dog’s blood stream and soft tissues, eventually making its way into the animal’s bones. How much lead is absorbed is directly affected by a dog’s circulating iron and calcium levels and other dietary factors. Eventually, at the end of the day, lead is eliminated in the feces or urine.
Causes of Lead Poisoning – In Real Time
Many things can contain lead and be potential sources of poisoning for domestic dogs. These include one or more of the following:
- Lead-based paint, paint chips and paint dust (often ingested during self-grooming by dogs living in older homes that are being renovated)
- Lead weights
- Fishing sinkers
- Toys and trinkets
- Bullets and lead shot
- Car batteries
- Grease and oil
- Combustion residue from burned buildings
- Stained glass framing
- Older board-game tokens
- Plumbing materials and supplies
- Drywall (sheetrock)
- Tar paper
- Lead foil
- Golf balls
- Drapery weights
- Leaded glass
- Contaminated foliage growing along roadsides or near smelters
Prevention of Lead Poisoning
The only way to prevent dogs from becoming poisoned by lead is to keep them away from anything that contains lead. Because most dogs are mouthy and naturally curious creatures, they tend to investigate things by licking or chewing on them. Owners must be diligent keeping all lead-containing items well out of their dog’s reach.
In the United States, lead-based paint was banned for use in residential dwellings in 1977, and was largely restricted from use even earlier in the 1960s. However, older houses are still likely to be contaminated with lead-based paint, which can contain up to 50% lead by weight. In 1991, the Center for Disease Control estimated that 74% of private residential homes in the United States that were built before 1980 still contained hazardous levels of lead-based paint.
Lead Poisoning in Dogs – Symptoms and Signs
Chronic lead intoxication is more common in dogs than in cats and other companion animals. It usually occurs after repeated exposed to lead over a long period of time, which causes the toxins to build up in the bloodstream. Most dogs poisoned by lead develop neurological and gastrointestinal symptoms, including vomiting, diarrhea, anorexia, belly pain, lethargy, weight loss, behavioral changes and intermittent seizures. In a nutshell, dogs with lead poisoning just feel plain lousy.
Owners of dogs suffering from lead poisoning may notice one or more of the following clinical signs, which are fairly nonspecific and can develop gradually (this is called being “insidious in onset”):
- Loss of appetite (inappetence; anorexia)
- Weight loss
- Abdominal pain; nausea (often severe)
- Mental dullness; stupor
- Hysteria; excitation; agitation
- Aberrant (peculiar) behavior
- Lack of coordination (ataxia)
- Blindness; other vision abnormalities
- Tremors; uncontrollable symmetrical shaking and/or twitching; asymmetric neurologic signs are inconsistent with lead poisoning
- Seizures (often intermittent)
- Anemia; pallor (pale mucous membranes)
- Excessive thirst/water intake (polydipsia)
- Excessive urine output (polyuria)
- Abnormal vocalization (barking, whining)
Dogs that live in older buildings which may or may not have been renovated have an increased chance of coming into contact with toxic amounts of lead, because they are at increased risk of being exposed to lead-based paint. Young dogs (puppies less than one year of age) also are at higher risk, because they absorb lead more easily through their digestive tract than do adults. Lead also crosses the blood-brain barrier in immature dogs more readily than it does in adults, putting puppies at a greater risk of developing central nervous system damage from exposure to toxic lead levels. Dogs that are deficient in calcium, iron, zinc or vitamin D tend to absorb lead more quickly than other dogs, because lead has the ability to bind to cells and tissues that otherwise would be bound to those substances. Lead poisoning can occur in dogs of any breed or mixed breed and in either gender predisposition.
Lead Poisoning in Dogs – Diagnosis and Test
The effects of lead poisoning often take days to weeks to develop to the point where a dog is noticeably sick. Even then, the signs usually are non-specific – such as vomiting, diarrhea and general malaise – which could be caused by many things other than lead poisoning. A veterinarian who is assessing a dog that has ingested lead usually will not find anything especially remarkable during the initial physical examination. Blood tests (a complete blood count and serum chemistry panel) and urine tests (a urinalysis) are routinely recommended for dogs that simply “aren’t doing right.” The results of these tests may suggest that the patient has gastrointestinal and/or neurological abnormalities, but then again they may not. Blood work and a urinalysis certainly won’t identify lead as being the culprit. However, they can reveal blood abnormalities, such as nucleated red blood cells, which are present in about half of the dogs with lead poisoning. It is extremely important for owners to tell their veterinarian about any history of their dog’s possible exposure to lead. This includes letting the veterinarian know if their house has been undergoing renovation, repainting or remodeling. Unfortunately, most of the time the owner will not have observed the dog licking or eating the lead-containing item. The owner may not even be aware that certain items have potentially toxic levels of lead in them –like golf balls, linoleum, foil and older game-board tokens.
A dog being evaluated for lethargy, vomiting, diarrhea and general depression could be suffering from a number of different things, such as parvovirus infection, food allergies, encephalitis, liver disease, pancreatitis, antifreeze toxicity, kidney failure, cancer (neoplasia) or simple dietary indiscretion, to name just a few. The veterinarian’s task is to work through the various differentials and narrow the list down to the most likely potential causes of the dog’s condition. In addition to routine blood and urine tests, the veterinarian may recommend abdominal X-rays (radiographs) and/or a serum bile acids test as part of the initial work-up. The results of those tests and procedures can be extremely helpful to rule out many of the possible causes of the dog’s symptoms. However, these tests are not specific and can’t be used to confirm a diagnosis of lead poisoning.
The gold standard for diagnosing lead poisoning is to measure the concentration of lead in the dog’s blood. This is referred to as the “blood lead level,” or “BLL.” A BLL test should be done in all cases where lead poisoning is suspected. The test is virtually non-invasive, relatively inexpensive and performed at a medical laboratory on a fresh sample of the dog’s whole blood. Blood lead levels greater than 35 mcg/dL, together with appropriate clinical signs, are diagnostic of lead poisoning. BLLs between 10 and 35 mcg/dL reflect significant exposure and probable lead poisoning if accompanied by appropriate clinical signs. A normal BLL result is less than 10 mcg/dL.
Dogs suffering from chronic exposure to lead (multiple exposures over a long period of time) may have low blood lead levels, because much of the lead has been sequestered into their bones.
Goals of Treating Dogs with Lead Poisoning
The primary goals of treating a dog that has been poisoned by lead are to stabilize the animal and manage its clinical signs, especially seizures and blood abnormalities such as anemia. An equally important goal is to remove any identifiable sources of lead that may still remain in the dog’s stomach or intestinal tract. Fortunately, treating dogs with lead poisoning is usually very successful.
Treatment Options for Dogs with Lead Poisoning
The first treatment task is to control any seizures and other neurological symptoms that the dog is having. Seizures, tremors and twitching are fairly common in dogs that have been poisoned by lead. This can be done with several different drugs, including diazepam and pentobarbital. The dog’s hydration status must also be managed, which may require placement of an intravenous catheter and administration of intravenous fluids. Once the dog is stabilized, any identifiable lead-based objects should be removed from its gastrointestinal tract. These typically are detected radiographically (by taking X-rays of the dog’s belly). Lead-based objects can be removed by stimulating vomiting (emesis), administering enemas, irrigating the whole bowel or removing the items surgically.
A number of different compounds are available to remove the remaining lead from dogs with lead poisoning. These compounds chelate or bind to lead molecules and remove them from the dog’s bloodstream. Eventually, the chelating agents and sequestered lead are excreted in the dog’s urine or feces. Many lead chelators can cause kidney damage and actually increase the absorption of lead from the digestive tract. Succimer (meso-2,3-dimercaptosuccinic acid [DMSA]) is the current treatment of choice in most cases; it is the least harmful to the kidneys, can be given orally or rectally and does not enhance gastrointestinal absorption of lead. Calcium disodium ethylenediaminetetraacetic acid (Ca EDTA) can also be used, and is especially useful in dogs with intractable vomiting that cannot tolerate oral medication. Activated charcoal, which binds to many toxins, does not absorb lead well and is not particularly useful in cases of lead poisoning.
Prognosis and Outlook
Dogs with mild to moderate symptoms from lead poisoning have a fairly good prognosis, as long as their condition is diagnosed and treated appropriately. Dogs that have lead embedded in their soft tissues and bones, and those that are showing neurological signs, have a more guarded prognosis.