What Does a Roundworm Larva Look Like?

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A roundworm is an internal parasite found in domestic dogs and cats, but also in wild animals, such as raccoons. Roundworm is a zoonotic infection – an animal infection transferable to humans and to which small children are particularly at risk.

Adult Roundworms

Adult roundworms live in an animal's intestine, laying millions of microscopic eggs, often over a short period of time. The eggs are then excreted in the animal's feces. Encysted larvae, or eggs, can remain dormant for long periods in body tissue and the environment, causing a risk of human contamination, particularly when small children put contaminated dirt or objects in their mouths.

Roundworm Larvae

Puppies and kittens can get encysted roundworm larvae from their mothers, at birth or in the milk. Some encysted larvae travel from the stomach into the lungs, are coughed up and then re-swallowed; other larvae move into the intestine and lay more eggs, which are excreted in the animal's waste.

Roundworm Detection

Adult roundworms look like short white tubes, or two to three-inch cut-up pieces of spaghetti, and are evident to the eye in your pet's vomit or feces. But the encysted larvae or eggs are so small they cannot be seen by the unaided human eye, only by microscope.

Finding Encysted Roundworm Larvae

In a fecal flotation test under a microscope, the larvae will appear round and dark in color, with a paler rim (a protective shell) around the far edge. Your veterinarian must do a number of these tests, looking for floating encysted roundworm larvae in your pet's feces.


While roundworms, once detected, can be eliminated from your pet in two or three treatments, you must never stop monitoring your pet for roundworms. The health of your pet and your family is at stake.

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