How to Tell If a Dog Has Worms

Unless a dog has a severe worm infestation, he might not show any physical symptoms. Don't assume an apparently healthy dog is worm-free unless you know he's been tested or is up-to-date on a veterinarian-recommended deworming program. One reason your veterinarian asks you to provide a fecal sample at your dog's regular checkups is so she can test for the presence of worms. Most worms affecting dogs -- and their eggs -- are too small to see without a microscope.

Puppy playing tug of war
A puppy is playing tug of war outside.
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Roundworms, or ascarids, usually are passed from the mother to her puppies during gestation, or in her milk. Affected puppies experience diarrhea, general unthriftiness, and the classic "potbelly" appearance. You might spot worms in the feces or in vomit. Your vet diagnoses roundworms by the puppies' physical appearance and by testing fecal samples. Puppies can receive roundworm dewormers as early as 2 weeks of age, with repeated dosing over the next weeks and months. While older dogs can become infested, most healthy adult canines have developed some resistance.


If your dog is over 7 months of age, your vet will conduct a blood test to determine if he's been exposed to heartworm. Your vet can start younger dogs on a preventive, since an infected dog takes at least six months to show symptoms. Dogs require another test six months after the initial one, with an annual test thereafter. Heartworm medication requires a veterinary prescription. Monthly heartworm preventive also gets rid of most other canine intestinal parasites. If your dog tests positive for heartworm, treatment depends on the severity of his infection. Generally, your dog receives a series of injections to kill off the heartworms, along with rest and limited activity for up to three months. Canines with large numbers of long heartworms can die not only from heart or lung disease but from related renal or liver failure. Even those with fewer, shorter heartworms -- who might not show clinical signs of illness -- can succumb from the infection.


Whipworm infestation is tough to diagnose, since these tiny creatures lay relatively few eggs. Your vet might require several stool samples to reach a definite diagnosis. Symptoms of heavy whipworm infestation include weight loss, diarrhea or bloody or mucous-covered feces. Whipworms can cause anemia in some canines. Your vet can prescribe medication for whipworm elimination.


Often, dogs with tapeworm infestation show no physical signs. Some might lose weight or experience diarrhea. An affected dog might engage in some butt-scooting. If you notice small, rice-like particles in your dog's feces or around his anus, he's probably got tapeworms. Standard dewormers usually won't eradicate tapeworms. Your vet can provide you with medication to get rid of these parasites, or give him a shot to kill off tapeworms. Avoid future infestations by using topical or oral monthly flea preventives on your pet, along with keeping him away from the carcasses of dead birds or animals.


These tiny worms latch on to your dog's small intestine, sustaining themselves on blood. As with roundworm infestation, puppies often become infested in utero or through mother's milk. In puppies, hookworm infestation can result in anemia and death. Symptoms include severe diarrhea or tarry feces. Adult canines can suffer from weight loss, weakness, lack of stamina and bloody diarrhea. Your vet can prescribe a dewormer to eliminate hookworms.