A large percentage of puppies are born with roundworms or ascarids in their tissues. These larvae are introduced to the developing puppy either through the mother's milk or in the mother's uterus before being born. Roundworms are most commonly found in puppies and may cause varying amounts of diarrhea, vomiting, and weight loss, often with an increased appetite. Some dogs will develop a bloated abdomen with roundworms or other types of worms. On occasion, dogs may even vomit up visible roundworms as well.
Hookworms are small, thin worms that attach to the wall of the small intestine and suck blood. Severe hookworm infestations may even kill puppies, as these worms can make puppies severely anemic. In older dogs, chronic hookworm infection may cause low stamina, decreased appetite, and weight loss. Other symptoms of hookworms in dogs include bloody diarrhea, anemia, and weakness.
Another common worm seen in dogs, tapeworms typically infect dogs that ingest fleas, or eat wildlife and rodents. In many cases, tapeworms cause no severe clinical symptoms, but are often diagnosed by finding tapeworm segments in the stool or near the rectum of affected dogs.
Whipworms are thread-like worms which typically live in the large intestines of dogs, and may cause symptoms such as mucousy or bloody stool, low appetite, and weight loss. These worms also suck blood and cause anemia. Whipworms are difficult to diagnose, as a microscopic exam of several fecal samples may be necessary to detect them. Whipworms can also be one of the most difficult worms to eliminate but they are both treatable and preventable.
Coccidia are intestinal parasites that overgrow typically in young puppies from boarding or pet store facilities, and may cause varying degrees of diarrhea, often with blood. Coccidia are not as readily seen in adult dogs, since they seem to have a more innate immunity to these parasites.