Some potentially lethal canine worms are not found in stool samples, although stool samples should still be a part of a dog's regular checkup. Many dog worms live in other organs other than those of the digestive system. When the worms release their eggs, the eggs often go into the blood, tears or urine instead of the dog's stool, according to "Dog Owner's Home Veterinary Handbook."
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Heartworms
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Heartworms can be lethal to dogs. Heartworms travel in a dog's bloodstream and eventually wind up in first the lungs and then the heart, according to the American Heartworm Society. Only blood tests can be done to test for adult or juvenile heartworms (known as microfilaria.) Stool tests will not work. Medication to kill microfilaria will not kill adult heartworms, and medication for adult heartworms will not kill microfilaria. This is why dogs receive blood tests for adult heartworms before being placed on a microfilaria prevention program.
Renal Worms
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Several species of tiny worms can infect a dog's kidneys. The most common are Capilliaria plica and Dioctophyma renale, according to veterinarian . Bari Spielman, writing for PetPlace.com. Dogs become infected by eating earthworms, frogs or fish that already are infected by the worms. Since the worms live in the urinary system, they deposit their eggs in the dog's urine and not the stool. Eggs appear in the urine, but not the stool.
Eyeworm
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Thalazia californiensis is a worm 1/2 to 3/4 of an inch long that lives in the dog's tear ducts. It releases its eggs in the dog's tears, to be drunk by flying insects such as flies, so the eggs will have no chance of winding up in the dog's stool. The eggs hatch in the insect and grow into larvae. When the insect drinks from another dog's face, the larvae crawl to the eyes. These worms can produce chronic conjunctivitis or other eye inflammations. Diagnosis is difficult, but examining the tears of a dog should reveal eggs of this worm.
Whipworms
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One family of worms, whipworms, do leave eggs in a dog's stool, but these eggs are incredibly difficult for even experienced vets to find, according to "Dog Owner's Home Veterinary Handbook." Examining several stool samples may not show signs of eggs. To diagnose whipworms, veterinarians often skip a stool test and look at the characteristic diarrhea they cause in a dog. Mucus and blood covers the stool. Dogs left untreated lose weight and become anemic. Several prescription deworming medications kill canine whipworms and other types of worms.
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