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Roundworms in Dogs

The most common parasite found in the intestines of dogs is the Roundworm. There are actually two types of Roundworms found in dogs, Toxascaris leonine and Toxocara canis, with the latter being the more common of the two. These unwelcome little guests can find their way into a dog in one of four ways:

By ingestion of Roundworm eggs. If a dog eats soil or feces containing Roundworm eggs, the eggs will hatch and the larvae will enter the walls of the small intestine. After moving through the circulatory system they then head towards either the respiratory system or other organs, and are often coughed up and reswallowed. Larvae still inside the stomach will mature into adults that will lay more eggs to be passed into the dog's feces.

By ingestion of another host. This is similar to the first case except that here the dog eats another animal already infected with Roundworms. Once digested, the larvae are released into the dog's system.

By larvae through the uterus. Once inside a dog's system, Roundworm larvae can seal themselves inside internal tissue, a process called encysting, where they can remain for months or even years. A bitch infected with encysted Roundworm larvae can pass them on to her litter, the larvae moving through the uterus and placenta and infecting the pups.

By larvae consumed through breast milk. A bitch infected with Roundworm larvae can also pass them onto her litter through breastfeeding.


A single female Roundworm can produce some 200,000 eggs per day, and the eggs themselves only take around 4 weeks to mature into adult Roundworms. The most common and obvious sign that a dog has Roundworms is the appearance of an enlarged belly, especially in puppies. The coat may also become noticeably dull and some dogs may tend to vomit and develop diahoreah. In more severe cases Roundworms can actually be seen in the vomit or feces, and are typically between 3-8 inches in length. More seriously, if the larvae have migrated to the lungs, this can lead to pneumonia.

Precautions and Treatment

The best way to deal with Roundworms is to consult with a qualified vet, as any medication will need to kill both the Roundworms and any larvae. They will normally recommend several courses of a suitable worming agent (some heartworm medications contain an ingredient that kills Roundworms).

People can also become infected with Roundworms, more commonly children who often play with soil and put their hands in their mouths. To reduce the risk don't allow kids to play in areas where dogs excrete. Note that direct contact with an infected dog rarely leads to human infection because eggs need to be ingested.

Submitted by Mike Thompson June 2012.