Intestinal parasites, or worms, are a plague to both dogs and cats. Most pets will harbor worms at some point in their lifetime. Puppies and kittens have a high incidence of intestinal parasites, and most receive de-worming treatment as part of their routine care. Roundworms, hookworms, and whipworms are the most common culprits of these infections.

“Roundworms are the most common intestinal parasite infecting dogs. Cats can get roundworms too, but it is not as prevalent,” says Dr. Allan Paul, a veterinary parasitologist at the University of Illinois College of Veterinary Medicine in Urbana.

Roundworms are spread when animals eat feces or soil contaminated with roundworm eggs. Mothers can also infect puppies through the placenta. Roundworms are spread to kittens through their mother’s milk. Adult roundworms set up shop in the intestine and live off ingested food. They multiply rapidly; one female can lay up to 200,000 eggs per day! A few eggs can lead to a large infestation.

Diarrhea and vomiting, leading to dehydration, are commonly seen with roundworms. Infected puppies have a distinct potbelly appearance. Adults are not seriously affected by roundworms. Puppies and kittens can become quite sick; they are more sensitive to dehydration.

“The warm temperatures of spring and summer are ideal for roundworm eggs to become actively infectious. Roundworm eggs are hardy. They are resistant to environmental changes and can remain alive outside for many years. There are no chemicals that effectively kill them. Live flame kills roundworm eggs, but most people are against torching their backyard!” says Dr. Paul.

Hookworms are also a problem for dogs and cats. These worms hook themselves to the intestinal wall and feed on blood. They are acquired by adults through skin penetration and ingestion of larvae. Puppies and kittens can be infected across the placenta and through milk.

Blood loss is the worst consequence of hookworms. Severe anemia—a decrease in red blood cells—is the result of extensive blood loss. Hookworms feed at several sites in the intestine. They release an anti-coagulant so clotting does not occur. The feeding sites continue to bleed after the worm moves on, and the result is a black, tarry stool. Bacteria can invade the body through these open wounds and cause infection.

Whipworms are a problem in the canine world, but cats do not become infected. “Whipworm eggs are tough organisms. They can survive adverse environmental conditions and are extremely resistant to drying,” says Dr. Paul.

Adults whipworms live in the large intestine and eat blood meals by attaching to the intestinal lining. The worms are passed in the feces. They can cause inflammation, anemia, and weight loss. Whipworms are a common cause of bloody diarrhea in dogs.

Veterinarians diagnose worms by taking a fecal sample and identifying any eggs found there. Consult with your veterinarian on how often feces should be screened for worms.

The good news is it is easy to get rid of worms with medication. Your veterinarian has de-wormers that should clear up the problem in a few weeks. Re-checking the feces is important to make sure all worms have been eliminated. To prevent or control intestinal parasites, consult your local veterinarian.