The Most Common Internal Parasites

The most common internal parasites in dogs are roundworms (especially the Toxocara species), hookworms (primarily Ancylostoma) and whipworms (Oxyuris). Reports suggest that more than 80 percent of all puppies will be born with, or quickly acquire, roundworms. These parasites live in the intestines and drain vital nutrients that growing puppies need. On rare occasions a puppy will vomit up roundworms, but worms are normally diagnosed when your veterinarian checks a fecal sample. Whipworms do not pass as many eggs as roundworms or hookworms, so repeated fecal checks may be necessary. Your veterinarian may elect to treat for them anyway based on clinical signs. Picking up after your dog is very important to reduce the chances of internal parasites being spread.


Roundworms can infect puppies before they are born and can also be transmitted via the dam's milk. Adult dogs get roundworms by accidentally ingesting eggs deposited on the ground. The immature larvae migrate through your dog's body and can cause damage to the liver and lungs. Puppies with roundworms often show a bloated abdomen, dull coat, diarrhea, and possibly intestinal blockages. Adult dogs develop some resistance, but even they can show the effects of roundworms.

It is very important that all puppies be checked for roundworms and dewormed. These parasites can also infect people. While they don't reproduce in humans, they can cause serious damage, even blindness, while migrating through tissues. Young children who play in dirt are at greatest risk.


Hookworms are nasty parasites. They are smaller than roundworms but with a set of mouth hooks that dig into the intestines and drain nutrients and blood. Again, puppies can be infected in utero or via their dam's milk. Hookworms can be ingested and can also penetrate the skin, and they cause skin lesions in people as they migrate through the body. Because of their voracious nature, hookworms can actually kill a puppy by making it severely anemic. Dogs with hookworms will show anemia, possibly bloody diarrhea, weight loss, and poor coats.


Luckily whipworms are not as prevalent as roundworms or hookworms. These are small intestinal parasites with a whiplike, tapering tail (hence the name). The eggs need to be ingested to complete their life cycle, but they can survive in the ground for long periods of time. Whipworms cause diarrhea, often with mucus and blood. Dogs with whipworms may defecate frequently and strain to do so. A large number of whipworms can be a serious drain on an adult dog, let alone a puppy. Whipworms are resistant to treatment, so repeated treatments may be necessary. It is also important to clean up the environment, or your dog can easily become reinfected. Cement runs may be bleached, while dirt runs may need to be dug up and replaced with fresh soil.

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