Roundworms of the Dog

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What is it?

Ascariasis is a parasitic infection of the small intestine caused by ascarids (a.k.a. roundworms), which are large non-segmented nematodes.

Toxocara canis is the most common roundworm of the dog. Toxascaris leonina occurs less commonly.

Baylisascaris procyonis is a roundworm of the racoon, but can occasionally infect the dog.

Eggs are extremely resistant in the environment, and can survive for years. 

Where can it be found?

It can be found worldwide.

How does infection occur?

Infected dogs pass unembryonated eggs through their feces into the environment. Eggs become embryonated (develop into third-stage larvae) and infectious in the environment. Another dog can then become infected by ingesting an embryonated egg with infective third-stage larva from the fecal-contaminated environment (direct life cycle). Another way in which infection can occur is by a dog ingesting a paratenic host (a host that harbors larvae in its tissues, e.g. rodents, rabbits, and birds) containing an infective third-stage larva in its tissue (indirect life cycle). Transmammary (through the mother’s milk) and transplacental (through the mother’s placenta) transmission are possible. Migration can lead to encysted larvae within the dog’s tissues, pulmonary (lung) damage and hepatic (liver) fibrosis.

What are the clinical signs?

It may be asymptomatic (have no clinical signs). If there are clinical signs, clinical signs include diarrhea, weight loss, failure to thrive or stunted growth in puppies, abdominal distension (“potbelly” appearance), poor haircoat, vomiting, and adult worms in feces or vomitus. Intestinal obstruction, intestinal rupture, and death are rarely possible. Coughing due to lung migration is also possible.

How is it diagnosed?

Diagnosis is commonly made via fecal flotation or freshly passed adult roundworm in feces or vomitus. Other diagnostic tools include ELISA (enzyme-linked immunosorbent assay) and PCR (polymerase chain reaction).

What are the treatment options?

Some of the medications your veterinarian may prescribe are pyrantel pamoate, fenbendazole, milbemycin oxime, or a combination product.

A follow-up fecal flotation is recommended 1 to 2 weeks following treatment.

How can it be prevented?

Prevention consists of deworming pregnant and nursing dams, deworming puppies, keeping your pet on good quality anthelmintic monthly prevention, as well as picking up feces promptly from the environment to help limit environmental contamination and spread of disease. Prevent your pet from coming into contact with another animal’s feces. Predation prevention to help prevent infection via ingestion of a paratenic host. 

The Companion Animal Parasite Council recommends monitoring for disease by performing fecal flotations approximately 4 times in the first year, and then approximately 2 times per year for patients on good quality monthly prevention. 

Can my dog infect humans or cats?

Zoonosis (infectious disease transmissible from non-human animals to humans) is possible, e.g. visceral larva migans, (VLM), ocular larva migrans (OLM), and neural larva migrans (NLM). Children typically become infected by putting contaminated soil or sand in their mouths. Dogs can infect cats.

For Veterinary Professionals, refer to our app, VetpocketTM, for more in depth reference material including treatment dosing guidelines.

*Disclaimer: The information is not intended to replace clinical judgment or guide individual care in any matter. Please check any information and values prior to use and use at your own risk.