Understanding Roundworms in Pets: Causes, Symptoms, and Prevention

Roundworms (Toxocara spp.) are among the most common intestinal parasites in dogs and cats, and they are readily visible in feces or vomitus due to their large, white appearance.

How Pets Get Infected

Mother dogs can pass the parasite to their developing puppies either in utero or through milk during nursing. Kittens are not infected in utero, but can become infected while nursing.

Adult roundworms reside in the intestines, where they lay eggs. Infected pets shed these eggs in their feces, which become infective once they reach the environment. Other animals can become infected by ingesting contaminated soil, licking the ground, or eating prey such as rabbits, rodents, or birds.

• Pot‑belly in puppies and kittens
• Coughing
• Dull, thin coat
• Vomiting
• Diarrhea
• Failure to gain weight

Roundworms are zoonotic parasites, meaning they can be transmitted from animals to humans. Children are especially vulnerable, typically acquiring infection by ingesting contaminated soil. In humans, migrating larvae can cause a range of conditions—known as larva migrans—including liver, lung, and nervous system involvement, and even eye damage that can lead to blindness.

Prevent infection by encouraging children to wash their hands after handling pets or playing outside, and keep sandboxes covered when not in use.

Diagnosis

Veterinary professionals usually detect roundworm infection by examining microscopic eggs in a fecal sample. Owners often discover visible worms in their pet’s vomit or stool, prompting a veterinary visit.

Treatment

Young pets are typically treated with an antiparasitic medication during their first veterinary visit. Most monthly heartworm preventatives also target roundworms and other intestinal parasites. Even if a fecal test is negative, a veterinarian may recommend deworming, as roundworms can sometimes be missed.

Prevention

Roundworm eggs remain infective in the environment for months to years, even under harsh conditions. Fresh feces are not infectious, but should be removed and disposed of immediately. A monthly preventative that includes roundworm coverage provides year‑round protection, and annual fecal exams are advised to confirm parasite freedom.

Sharing litter boxes or outdoor bathroom areas can spread roundworms between pets, so new animals should be tested for parasites before introduction to the household.

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About the Author: Siri