Roundworm in Dogs

What are roundworms?

Roundworms (Ascarids) are a common intestinal parasitic worm found in many species. There are two species which affect dogs, Toxocara canis and Toxascaris leonina. Toxocara canis is more commonly found in dogs. They feed upon the intestinal contents, competing with the host for food.

Roundworms are around 3 - 5 inches long & spaghetti like in appearance. 

How do dogs become infected with roundworms? 

There are three modes of transmission, all of which occur when the dog consumes the infective eggs. It is possible for larvae to be encysted in the tissues from an earlier infection.  

• Transmammary transmission (Toxocara dogi): When a dog is infected with roundworm, some larvae migrate to other tissues in the body. Pregnancy  re-activates these larvae which migrate to the mammary glands & are passed onto the kittens via the mother's milk.

• Hunting: Rodents can act as intermediate hosts to roundworm & when a dog kills & consumes it's prey.

• Environmental: Dogs ingest roundworm eggs containing infective larvae from the environment such as soil, or when they come into contact with the faeces of an infected dog.

Life cycle of roundworm: 

Eggs are passed in the faeces, at this stage they are not infective. Once in the environment they develop into what's known as "second stage larvae". This takes around three weeks.  It is at this time that they become infective. Eggs can survive in the environment for months. 

The dog ingests the egg containing the infective larvae. Once inside the dog they hatch in the dog's intestinal tract. The larvae migrate to the liver & other organs. In the liver they develop into the third stage. They then enter the bloodstream & migrate to the lungs. Once in the lungs where they develop into the fourth stage larvae. They are coughed up & into the throat & then swallowed, re-entering the intestinal tract for a second time. Once in the intestinal tract they mature & begin to mate. The female lays her eggs which are passed in the faeces & so the cycle begins once again. 

Some of these become encysted in the tissues where they are inactive (or dormant). When a dog is wormed, the worms in the intestines are killed but the encysted larvae. 

In rodents, the animal swallows the roundworm eggs which hatch inside the rodent's intestinal tract & then migrate to the organs where they become encysted. They are not able to complete their life cycle in rodents, but if dogs eat infected prey, they can become infected. 

Life Cycle of Toxascaris leonina:

As with Toxocara canis, the eggs of Toxascaris leonia are passed in the faeces where they develop into the second stage & become infective. The larvae are consumed by the dog they hatch in the dog's intestinal tract. 

There is no transmammary transmission with Toxoscaris leonia. 

What are the signs of roundworms in dogs?

• Poor coat condition

• Diarrhea

• Vomiting (if infestation is heavy there may be worms present in the vomit)

• Pot bellied appearance

• Severe cases can lead to pneumonia & intestinal & bowel blockage

• Coughing

How is roundworm in dogs diagnosed?

Diagnosis is performed by examination of the feces for eggs. 

Are roundworms dangerous to dogs?

If the infestation is severe roundworms can lead to pneumonia & intestinal blockage. Also, as the roundworms are competing with the dog for food, it can result in your dog not receiving enough nutrients & becoming malnourished. This is usually seen in kittens. 

What's the treatment for roundworms?

There are many effective medidogions to treat roundworms.  

Can I catch roundworms from my dog?

Toxocariasis is a disease in humans caused by infection of the roundworm egg. Most cases have been identified as those of T. canis. In humans roundworms can't go past "stage 2" (larval stage). As with infection in rodents, the larvae migrate to various tissues in the body (causing a disease called visceral larva migrans or toxocariasis) including the lungs, brain, eyes & liver. 

There are two forms of toxocariasis: 

• Ocular larva migrans (OLM) results from the larvae entering the eye, causing an inflammatory response, which leads to damage to the eye, in severe cases it can result in blindness. 

• Visceral larva migrans (VLM): The larvae migrate to the various organs and cause an (inflammatory immune response) which leads to damage to the organs.

The larvae can remain alive for many months, causing damage by migrating through tissues.

How do I prevent roundworms in my pet?

• Regular worming

• Preventing hunting behavior

• Regular cleaning & removal of faecal waste in your dog's litter tray

Please note:

The medical articles on this site have not been written by a veterinarian & should not be considered a replacement for a veterinarian visit. The articles are provided for informative purposes only.

Always seek immediate veterinary advice for any problems (health or behavioral) in your pets. 

While great care has been made in the creation of these articles, we cannot guarantee the accuracy or omissions on these pages. If in any doubt whatsoever, seek professional medical advice.