Toxocara (Roundworms) and Your Dog | Companion Care
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Roundworms And Your Dog

Toxocara is more commonly known as roundworms

Roundworms are very common in the UK – in fact studies have shown that over 20% of dogs and cats may be actively infected at any one time! This means that your dog can be at risk of picking up worms whenever you head outside. Picked up from contaminated faeces, or even from the soil, roundworms can cause diarrhoea and poor growth, and also have human health risks.

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More about roundworms and your dog

Roundworms are white, round-bodied worms, and can get up to 18cm long! These worms spend most of their life within the gut of dogs, feeding on intestinal contents. Roundworms reproduce by laying eggs within the intestine. These eggs are passed out with faeces, mature for up to seven weeks, and then become infectious. Dogs then ingest these infectious eggs, which hatch into larvae. Importantly, larval roundworms can travel out of the gut to a wider range of tissues, including multiple organs such as the liver and lungs, skeletal muscle and the gut wall, where they may form cysts. This allows dogs to maintain a level of infection, and bitches can pass on infections to their puppies via the placenta or milk. This infection of puppies is the most common route of infection.

Sadly, toxocara can also infect humans and, while usually harmless in adults, can cause serious damage to children’s eyesight.

A roundworm infection, also called toxocariais, can be picked up by a dog in one of four ways:

  • By eating infectious eggs, in contaminated soil or faeces
  • By eating another infected animal, which can include rats or birds
  • Puppies can get roundworms through their mother's milk
  • Puppies can be born infected if their mother is infected

With so many sources of infection, and a high prevalence of toxocara infection in dogs in the UK, roundworms are a risk for all dogs. Certainly, it would be impossible to keep a dog away from all sources of infection, as this can include soil!

In a healthy, adult dog there may be no outward signs of a roundworm infestation beyond visible adult worms in the faeces or vomit. However, in severe infestation, or in dogs that are very young or have a poor immune system, you may also see:

  • A pot belly
  • Diarrhoea
  • Weight loss, or poor growth
  • Poor coat quality

Sadly, a heavy infestation in a young puppy can even be enough to kill.

If your dog is experiencing any of these signs and you suspect that they might have worms then you should make an appointment with your local Companion Care as soon as possible.

Thankfully, although you can’t stop your dog being exposed to roundworms, there are lots of options for preventing an infestation developing. Worming treatments can come in the form of tablets or spot-ons, and often manage a range of parasites including roundworms.

The best parasite protocol for your dog will depend on you, your dog, your lifestyle and even the season, and your vet can help you decide which regime works best for you.  However you choose to manage worms in your dog, make sure to speak to a vet about the best anti-parasitics on offer, as many over the counter treatments have poor efficacy. 


If you think your dog might have a roundworm infection, the best thing to do is to go to your vet. They can do a full physical examination, and check your dog over from nose to tail! If there is a risk your dog may have worms, your vet will prescribe a worming treatment suitable for your pet, which should eliminate the worms. They can also help you plan a worm prevention plan going forward too, to make sure your dog stays protected. 

If there is any doubt, your vet may recommend a faecal test. This will look for evidence of worms, such as eggs, and may also look for bacteria within the faeces. 

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Sadly, humans can also become infected with toxocara, and this includes toxocara found in dogs and in cats. Infection is actually not uncommon – one study estimated that over 13% of the population of the USA had antibodies to toxocara! In the UK the incidence is lower, about 2%, but this is still one in fifty of us!

Many people who are infected with toxocara roundworms show no signs at all. However, some people, especially those who are young, or have a poor immune system, can develop problems as the larvae can migrate to the organs and the eyes. This can cause a range of signs depending on the body systems affected, however if an eye is affected (a condition called ocular larval migrans) a possible outcome is blindness. 

Advise to protect you and your family’s health:

  • Make sure your pets are kept up-to-date with their worming treatments
  • Promote handwashing after playing with pets, or playing outside
  • Clean up after your pet as quickly and frequently as possible – as Toxocara roundworm larvae take time to mature in faeces, fresh faeces is not a risk for human infection
  • Teach children it can be dangerous to eat soil
  • Cover sandpits when not in use – pets and wildlife can use sandpits as bathrooms, making them hotbeds for infection.