Toxocara canis is a roundworm which primarily affects dogs, and symptoms can be severe in young puppies. Although it doesn’t commonly cause disease in adult dogs. More importantly, Toxocara canis can infest humans as an intermediate host, causing several different syndromes. So what do we need to know and do about it?

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What are Toxocara worms?

Mature roundworms feed on the partially digested food located in a dog’s intestines. The parasite takes nutrients and nourishment away from the dog. Puppies are more susceptible to roundworms, largely because their immune systems are not fully developed. Toxocara is also more common in warm and wet areas.

If your dog is showing symptoms of having roundworms or if you visually see “spaghetti type” worms in his vomit or stool, he should be seen by a veterinarian as soon as possible. Untreated roundworms can cause malnutrition and could lead to intestinal obstruction or rupture.

Toxocara Canis is the most common parasitic roundworm found in dogs. This species of roundworm can be transmitted to people by contact with contaminated faeces or soil.

What is the lifecycle?

When eggs are ingested, they hatch into larvae. Larvae travel through tissues such as lung, liver and muscle. In adult dogs’ larvae often become encysted in tissue and remain dormant. In dogs less than year-old larvae more commonly enter the lungs, where they are coughed up and swallowed. Once back in the intestinal tract these mature larvae become adult worms, which in turn produce more eggs.

Encysted larvae can also be found in intermediate hosts such as rabbits and mice. If a dog ingests these already encysted larvae, they can mature into adult worms in the dog’s intestine, regardless of the age of the dog.

If a dog with encysted larvae were to become pregnant, Toxocara larvae can travel across the placenta to the lungs of the unborn puppies. This in utero transmission doesn’t cause problems until the puppies are born, at which point larvae are coughed up, swallowed, and become adult worms. Likewise, Toxocara larvae can be found in mammary tissue, and can be transmitted to puppies during lactation. For this reason, many puppies will have an active roundworm infection in the first few weeks of life.

Symptoms of Toxocara in Dogs

The symptoms are very variable, and adult dogs especially rarely show signs. However, the symptoms may include:

  • Mild to severe diarrhoea
  • Vomiting
  • Gagging
  • Weight loss
  • Weakness
  • Dull hair coat
  • Poor skin condition
  • Loss of appetite
  • Abdominal pain – Whimpers or cries out.
  • Distended abdomen – Pot belly appearance due to a large infestation of roundworms in the intestines
  • If roundworms have travelled into the lungs, coughing and/or pneumonia may occur.
  • Stunted growth in puppies
  • Visible worms in the dog’s vomit or stool
  • Anaemia
  • Abdominal obstruction or rupture

Causes of Toxocara Canis in Dogs

Toxocara Canis can be transmitted by:

  • The roundworm larvae can be transmitted before birth or through the mother’s milk to the puppies.
  • If the dam ever had roundworms and was treated; she may still carry dormant (encysted) larvae in her tissues.
  • These dormant roundworm larvae can revive and pass on to her puppies. 
  • Dogs can become infected with Toxocara by ingesting faeces or soil which is contaminated with larvae.
  • If the dog eats an infected animal (rat, mice, birds) he may contract the roundworm.
  • Earthworms may also carry roundworm larvae, which can be transmitted to the dog if they are ingested.

Diagnosis of Toxocara Canis in Dogs

The vet will want to know the symptoms you have observed and when they started. They may also want to go over your dog’s medical history, vaccination, and deworming records. The veterinarian will then perform a physical examination on your dog which could include taking the temperature, weight, and blood pressure, listening to the lungs and palpating the abdomen area.  

The vet may recommend a complete blood count and the analysis of a faecal tests. The faecal sample is then examined under a microscope and checked for roundworm eggs. The veterinarian may also choose to run a faecal flotation test. This test mixes the faeces matter with a chemical solution which is placed in a test tube and spun down in a centrifuge.  Roundworm eggs and cysts will float to the top of the test tube.

Treatment of Toxocara Canis in Dogs

Puppies and dogs diagnosed with Toxocara canis will need to be de-wormed. Typically, the wormer is given over a few weeks.  The treatment goal is to kill the mature roundworms and their larvae. Fortunately, the worms are relatively easy to kill with most licensed worming medication available from your vet, a pharmacist, or an SQP being effective. Some medications available over the counter in supermarkets (not those dispensed by a pharmacist or SQP) may be less efficacious, and wouldn’t usually be recommended if there is a suspicion of an active infestation.

Elderly dogs and puppies with a severe infestation of Toxocara canis may need to be hospitalised. Once hospitalised, the patient can receive 24/7 supportive care. Anaemic (low red cell count) dogs may require a blood transfusion, supplements, and B-12 injections.

If there are other pets in the household; they should also be treated for roundworms.

Your pet’s home must also be treated for roundworms. Your dog’s kennel, bedding, blankets and toys should be cleaned. The infected dog’s faeces should be removed from the garden or local area where you walk. Carpets and tile flooring should be thoroughly cleaned. If you have small children who play in the garden, the area should be professionally treated for roundworms. 

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