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The dog roundworm Toxocara canis is a worm that affects dogs throughout the UK. It can cause serious disease in puppies and can be transmitted to humans. Roundworm control is the most important consideration in puppy parasite management. By the end of this module you will:

  • know how puppies can become infected with roundworm
  • understand why puppies need to be wormed
  • know the recommended worming schedule for puppies
  • know what to check before selling a wormer.
  • The most common way for puppies to become infected with roundworm is by transmission from the mother before birth.
  • In adult dogs infected with roundworm, the larvae (immature forms of roundworm) may be present in a dormant state in the dog's tissues. This usually causes no harm to the dog.
  • During pregnancy, the larvae may become activated.
  • The larvae can pass from the mother to the liver of the puppies via the placenta.
  • In the puppies the roundworm larvae migrate from the liver to the lungs. This causes the puppy to cough and swallow the larvae.
  • In the stomach the larvae then develop into adult worms.
  • Roundworm larvae can also be transmitted to the puppies in the mother's milk, but this is a less important route of infection in puppies. The swallowed larvae develop in the stomach into adult worms.
  • Adult worms lay eggs in the puppy's intestines and are then passed out in the faeces.

Roundworm infection in puppies may not be noticeable, or it can lead to mild signs such as a pot-bellied appearance and a cough. Puppies infected with high numbers of worms can be lethargic and fail to grow or gain weight. Severe roundworm infection in young pups can result in sudden death at a few days of age because of migration of large numbers of larvae to the lungs, or obstruction of the intestines by large numbers of worms.

As well as causing severe illness in the puppies, roundworms lay eggs in the puppy's intestine and these can end up in the environment in the faeces of the puppies. The puppies' mother can also become reinfected with roundworm resulting in eggs being deposited in her faeces.  The presence of roundworm eggs in the environment increases the chance of people being infected with roundworm. 

Roundworm infection occurs when people (usually young children) ingest infective eggs in contaminated soil or sand, or from unwashed hands or vegetables, or toys that have been in the garden, or from direct contact with pets, including puppies. 

Roundworm infection in humans can result in serious, and even fatal, disease. Some people are more vulnerable than others to roundworm infection: young children are more likely than others to accidentally ingest infective eggs; people who are immunosuppressed (because of illness or medication) might be more likely to develop infection than people with a strong immune system.

Good hygiene (including house training puppies and handwashing) and reducing environmental contamination with roundworm by picking up faeces are all very important for preventing spread of roundworm. Worming medicines also play an important role in controlling roundworm.

The aim of worming puppies with worming medicines is to prevent roundworm disease in the puppies and to suppress roundworm egg output.

Puppies need to be given a wormer that is effective against roundworm when they are 2 weeks old and then every 2 weeks until 2 weeks after weaning, then every month until they are 6 months old.  Bitches often become reinfected with roundworm during the suckling period, so parasite specialists recommend roundworm treatment should be started in nursing bitches at the same time as their puppies.

After 6 months of age, dogs should be wormed regularly, usually every 3 months, or monthly if they hunt or live with people who are more susceptible than normal to roundworm infection.

Non-prescription products for controlling roundworm contain one or more of the following drugs:







A few products are licensed for the control of roundworm in puppies from the age of 2 weeks (see the table below) There are also products that contain a drug that is active against tapeworm as well as roundworm for use in puppies from the age of 2 weeks, and many more products licensed for use in puppies from the age of 6 to 8 weeks. Wormers come in the form of tablets, liquids, pastes, granules and spot-ons. It is worth finding out if the owner has a preference because this might affect how likely they are to use it properly. It is usually easier to give a liquid or paste rather than tablets or granules to a 2-week old puppy. There is no need to continue with the same wormer used by a breeder. If the puppy is imported, there is the possibility of infection with exotic parasites and the owner should be referred for veterinary advice.

Puppies may become infected with other common roundworms such as hookworm and whipworm. Regular worming to control Toxocara roundworm will usually be sufficient to control these other roundworms. Some products are specifically licensed to control hookworm and whipworm as well as Toxocara roundworm. Check the product information.

Adverse effects (side effects) are rare with non-prescription wormers when used at the recommended doses. They sometimes cause mild and short-lived vomiting or diarrhoea. 

There are certain things you should check before selling a worming product:

  • Which parasites the product is licensed to cover. Although different products might have the same ingredients, they may have different licensed uses.
  • What species the product is intended for.
  • That the product is suitable for the animal's age. 
  • That the dose is correct (for the animal's weight). It is essential to weigh the puppy accurately for each dose.
  • How often it should be used.
  • The expiry date.

Remind the owner to read the product information before using the product.

Practical exercise

Become familiar with your product range. Find out what products there are for worming puppies. Check the package information for the minimum age and the parasites covered by the product.


You can listen to a complete podcast of the module below by pressing play or use the download link on the right hand side of the player to download the podcast to your mobile device.

Test yourself

To do the CPD quiz and receive your certificate, just hit the play button on the video below and enter your name and email address before you start.


ESCCAP. Worm control in dogs and cats. ESCCAP Guideline 01 Second edition, September 2010.

Fahrion AS et al. Patent Toxocara canis infections in previously exposed and in helminth-free dogs after infection with low numbers of embryonated eggs. Veterinary Parasitology 2008; 177: 186-9.

Fisher MA et al. Studies on the control of Toxacara canis in breeding kennels. Vet Parasitol 1994; 55: 87-92.

Jacobs DE. Control of Toxocara canis in puppies: a comparison of screening techniques and evaluation of a dosing programme. J Vet Pharmacol Therap 1987; 10: 23-9.

Jacobs DE, Fisher MA. Recent developments in the chemotherapy of Toxocara canis infection in puppies and the prevention of toxocariasis. In: Lewis JW & Maizels RM (Eds), 1993, Toxocara and toxocariasis: Clinical, epidemiological and molecular perspectives. Institute of Biology. London  pp: 111-6.  

Overgaauw PAM, Van Knapen F. Veterinary and public health aspects of Toxocara spp. Vet Parasitol 2013; 193: 398-403.

Schnieder T et al. Larval development of Toxocara canis in dogs. Vet Parasitol 2011; 175: 193-206.