Many of you already know that chocolate can make your cat or dog sick, but did you know that onions can kill? I learned this in my second year in veterinary school. But I didn't really appreciate it until the big onion incident that occurred during my senior year. Well, maybe the incident wasn't all that big; it involved only one dog. But it was my own dog, Max, a 72-pound adult boxer. And it nearly killed him.
Depending on their size, pets may not have to eat much onion to get sick. One-fourth of a cup can make a 20-pound dog sick, and several cups may be needed to make a large dog sick. Cats are even more sensitive.
These onions can be fried, as in onion rings; dehydrated, as in Lipton soup;
or prepared in some other tasty form, such as sauteed with mushrooms and steak. In a scattered rash of cat cases in the late 1990s, the culprit was baby foods flavored with onion powder.
Veterinarians often feed meat baby food to sick cats that won't eat their regular foods. When baby food formulations suddenly changed, some cats took a turn for the worse while under veterinary care. Because of public concern the companies involved no longer include onion powder in their baby foods.
In Max's case, the onions were fried, dried and then left on the coffee table by my roommate before she left for the weekend. I never saw the pound or so of deadly cuisine. All I found was an empty bag and drool on the floor.
TEST RESULTS
If I had known what was in the bag, I would have taken Max to my veterinarian immediately. Instead I took him two days later, after the normally boisterous prankster collapsed while exercising.
We performed a bunch of diagnostic tests, and on examining the blood work, found the telltale signs -- little purple clumps in his red blood cells that virtually screamed onion toxicity.
Onions cause toxicity by oxidizing an oxygen-transporting protein called hemoglobin in the red blood cells. When oxidized, hemoglobin forms clumps that can't carry oxygen as well. These small clumps, called Heinz bodies, can be seen in the red blood cells when the blood is viewed under a microscope.
Although a number of other compounds can cause these clumps, when veterinarians see Heinz bodies in many cat or dog red blood cells, onion toxicity is top on their list.
Normally, in dogs with onion toxicity a moderate number of red blood cells may contain Heinz bodies. In Max's case, most of the red blood cells carried the protein clumps.
Heinz bodies don't usually cause life-threatening problems themselves; the red blood cells can still carry oxygen, just not as efficiently. Heinz bodies cause problems by decreasing the red blood cell life span. As a result, the onion eater becomes anemic.
If a large amount of onions is eaten at one time, the pet may develop a sudden anemia several days afterward. If the dog or cat eats a small amount of onions every day for many days, he may gradually develop anemia over weeks to months.
Onion toxicosis is not a tremendously common occurrence. It's a good thing, because patients that do develop toxicosis often need to be hospitalized for several days. In cases of severe anemia, they may even need a lifesaving blood transfusion. Max did. Luckily, like Max, most victims of onion over-ingestion respond well to treatment and recover.
Relatives in the allium genus such as garlic and chives can cause the same problems as onions, but since they're used in small amounts, dogs and cats aren't likely to ingest a toxic quantity.
Onion toxicosis is characterized by signs associated with anemia and low oxygen, such as lethargy, weakness, red urine, decreased stamina and pale or bluish gums, especially with exercise. Although they are not a common cause of these signs, consider onion toxicosis if you see these signs and know that your pet has gotten into onions recently.
DON'T WAIT
If by some freak occurrence, your dog or cat does engage in an onion feast, bring him to your veterinarian immediately. She may induce vomiting or administer a product to help decrease the absorption of the onions. If you take this trip in time, your onion eater may be spared many or all of the hazardous sequelae of onion ingestion, and you may be spared the much larger bill associated with intense hospital monitoring and a several-night stay.
Incidentally, a few other human foods -- chocolate, coffee beans, macadamia nuts and extremely fatty foods -- can cause serious problems when fed in relatively small amounts. And ingestion of large amounts of grapes or raisins has been associated with kidney failure. Toxicologists don't know whether the grape is the problem or a residue or a contaminant is to blame.
For more information visit the ASPCA National Animal Poison Control Center at
www.aspca.org. To consult with a veterinarian at the Center's emergency hot line for a $45 fee, call (888) 426-4435.
Written by Sophia Yin, DVM, a small-animal veterinarian in Davis
