Canine Intestinal Parasites – Dogs with Roundworms

Roundworms are the most common dog intestinal parasites – and especially so in young puppies, which are often infected at birth, or soon thereafter.

The larvae of one of the roundworms – Toxocara canis – lie dormant in the tissues of most of the adult female dogs. Hormonal changes during pregnancy can activate these larvae, which then migrate through the placenta to infect the unborn puppies.

Some immature forms of canine roundworms can also be transmitted through the nursing mother’s milk, although this is a less common route of parasite infection. Puppies can also become infected by eating dirt or feces containing worm eggs and larvae, by licking contaminated fur or paws, or even by drinking contaminated water. Most adult dogs become infected through contact with worm eggs and larvae in the environment.

The life cycle of canine roundworms in dogs

After being swallowed, the roundworm eggs hatch in the dog’s stomach. The larvae then invade the stomach wall, and are carried by the blood to the liver.

From there, they migrate to the lungs, are coughed up, and are re-swallowed.

The parasites worms eventually make their way to the small intestine, where they spend their adulthood and produce eggs (more than 100,000 eggs per day!).

In adult dogs, canine roundworm larvae can migrate to tissues and become dormant. The dormant larvae are reactivated during pregnancy and are spread through the placenta to the unborn puppies.

While most infected adult dogs show no sign of infection, they continue to shed worm eggs and larvae in their feces, and can quickly contaminate a large area, contributing to the spread of infection.

Worm eggs and larvae can survive for many months in the environment, even in extreme conditions – which may help explain why intestinal worm infections are so widespread.

More about the symptoms of roundworms in dogs