How Do Dogs and Cats Get Worms?

Puppies and kittens are born with intestinal worms. This occurs because worms resting within the mother's body are stimulated to grow by hormones secreted during pregnancy. The newly developed worms within the mother pass through the placenta (transplacental) and into the young before they are born. In addition, worms are passed through the mother's milk (transmammary) to the young. Puppies, kittens, and female dogs that are nursing should be wormed routinely.

Adult dog and cats pick up worms from eggs that stay in the soil after pets have defecated. Some worm eggs survive for years in soil. Pets also pick up worms from:

  • Eating fleas
  • Catching prey, such as mice and snails
  • Eating feces of other pets and farm animals
Types of worms in dogs and cats

Worms are internal parasites that drain pets of blood and nutrients. Dogs and cats get worms that can be classified by shape into round or flat. Three types of round-shaped worms (nematodes) live in pet intestines: roundworms, hookworms, and whipworms. Two types of flat-shaped tapeworms (cestodes) live in pet intestines and other organs, including the liver: echinococcus and taenia. Dogs commonly get hookworms, whipworms, roundworms, and tapeworms. Cats commonly get roundworms, hookworms, and tapeworms, but not whipworms.

Pets can also get lungworms, esophageal worms, bloodworms, kidney worms, liver flukes, and intestinal protozoa. The most common pet worms are roundworms, and hookworms. Heartworms (Dirofilaria immitis) are not intestinal parasites but are parasites that live in the heart. Heartworms are not spread like regular intestinal worms, but are spread by mosquitoes. They infect both cats and d ogs and can cause death.

Key facts about worms in dogs and cats
  • Over ¾ of fecal exams do not find parasites present in feces.
  • Because puppies & kittens are born with worms, they should be dewormed regularly.
  • Some worms that infect pets also infect people.
Which pets are most at risk for worms?

Almost universally, puppies and kittens have intestinal worms. Puppies and kittens whelped in large kennels or in unhygienic conditions have the greatest worm burdens. Pets using pet parks, doggy day cares with communal potty areas, farmyards, and city streets where feces is on the sidewalk are prone to having worms. Pregnant and lactating females have worms. Pets kept in humane shelters generally have intestinal worms.

Recommended products for dogs and cats with worms:
Max's Tip

To prevent human infections, pets in homes with children, immune-compromised individuals, or elderly persons should be dewormed at least every three months.