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Answers from vets about your pet:

What are Roundworms and Why Should I Care?

Reviewed by Peter Kintzer DVM, DACVIM on Monday, April 14, 2014
Posted December 16, 2013 in Dog Diseases & Conditions A-Z


Dr. Mike Paul offers advice on how to choose a veterinarian that suits your needs and the needs of your pet(s).

What are they?

Roundworms are the most common intestinal parasite in dogs and cats. The adult worms are round and range in size from less than two inches to almost 6 inches in length. According to the Companion Animal Parasite Council, a survey conducted in 1996 using samples collected from across the United States found that more than 30% of dogs younger than 6 months of age were shedding roundworm eggs and other studies have shown that virtually all pups are born infected. Other surveys have found more than 25% of cats infected.

How does my pet get roundworms?

Because the larval stages of the worms migrate inside the animal, some of the worms become encysted and lie dormant in the host animal’s organs. When the female becomes pregnant, those hidden parasites can become active, mature, and be passed to the puppies or kittens across the placenta before they are ever even born. Sometimes the worms pass into the mother’s milk so the young ones are exposed again when they are nursing. Cats and dogs can also become infected by licking and/or eating grass and dirt and other soiled items that contain infective eggs or by eating prey animals that have already been infected.

Puppy RunningWhat disease does it cause in my dog or cat?

The migrating larvae travel through the body causing damage primarily to the liver and the lungs with most of the clinically significant damage occurring in the lungs and resulting in coughing and respiratory problems. Once adult worms form in the gastrointestinal tract, your puppy or kitten may develop vomiting, diarrhea , bloating and abdominal discomfort.

Can my pet give the worms to me?

Roundworms are not transmitted between people to other people. And they are not directly passed from dogs and cats to people. Affected dogs and cats shed eggs in their feces. The eggs mature into the infective stage of the parasite in the environment and are then swallowed with dirt that is either eaten on purpose (pica) or inadvertently (through inadequate care and hygiene). The infective larva do not progress to adult worms in people but the migrating larvae leave the intestines and find their way to other organs such as lungs, liver, or eyes and cause damage and disease

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Mike has more than 35 years of experience in companion animal veterinary practice and is a valued member of IDEXX’s Pet Health Network team since 2013.