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The cat roundworm Toxocara cati is a common parasite that can infect cats throughout the UK. It is related to the dog roundworm Toxocara canis. It can cause serious disease in kittens and, like dog roundworm, can be transmitted to people to cause serious, potentially fatal, illness. Roundworm control is the most important consideration in kitten parasite management. By the end of this module you will:

  • know how kittens can become infected with roundworm
  • understand why kittens need to be wormed
  • know the recommended worming schedule for kittens
  • know what to check before selling a wormer.

The most common route of infection with Toxocara roundworm in kittens is via their mothers' milk (transmammary transmission). It can be assumed that every kitten will be infected with Toxocara in this way.

  • Adult cats commonly become infected with roundworm through ingestion of infective eggs in the environment.
  • In adults cats, the larvae (immature forms of roundworm) released from the eggs can migrate to tissues in the body where they remain dormant. This usually causes no harm to the cat.
  • When a female cat becomes pregnant, the larvae migrate to the mammary glands and are excreted in the milk she produces for the kittens.  
  • The larvae develop into adult worms in the kitten's intestines. There they mate and produce eggs, which are deposited in the faeces.
  • The larvae may also migrate from the intestines to the liver and then to the lungs, where they cause the kitten to cough and swallow the larvae.

Kittens infected with roundworm may not show any signs at all, or they might have a mild pot-bellied appearance and/or a cough. If kittens are infected with large numbers of roundworm larvae they might have severe breathing problems, be lethargic, have poor weight gain and fail to thrive. Severe infections in young kittens can result in sudden death at a few days of age if large numbers of worms cause a blockage in the intestines.

As well as potentially causing severe illness in kittens, the eggs laid by roundworms can end up in the environment in the faeces of the kittens. The kittens'  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 kittens. 

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 at increased risk of infection.

Good hygiene is central to preventing roundworm infection in people. Toxocara eggs can survive in the environment for years, so removing faeces from the environment and preventing contamination (for example by covering sandpits) help control the spread of roundworm. However removal of cat faeces from the environment is not usually practical and so using worming medicines in cats and kittens is very important in helping control the spread of roundworm.

Kittens may become infected through the ingestion of eggs in the environment from other common types of roundworm such as Ancylostoma tubaeforme (hookworm) and Toxascaris leonine. Regular worming to control Toxocara roundworm should be sufficient to control these other roundworms. 

The aims of worming kittens are to prevent disease in the kittens and to suppress roundworm egg output.

Kittens need to be given a wormer that is effective against roundworm when they are 3 weeks of age, and then every 2 weeks until 2 weeks after weaning, and then monthly until they are 6 months old.

After 6 months of age, cats should continue to have roundworm protection, either monthly or 3 monthly (see the module on adult cats for more on this).

As queens often become re-infected during the suckling period, starting roundworm treatment in nursing queens at the same time as the kittens is recommended.

The later starting age for the treatment of kittens (at 3 weeks) compared to puppies (at 2 weeks) is because kittens, unlike puppies, do not become infected before birth, only when they are born and suckling.

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




A few products containing fenbendazole or piperazine are licensed for the control of roundworm in kittens from the age of 2 weeks. They are in the form of paste, syrup, suspension or tablets.

There are also products that contain a drug active against tapeworm as well as roundworm for use in older kittens. It is worth finding out if the owner has a preference for the formulation of wormer because this might affect compliance. It is usually easier to give a liquid or paste rather than tablets or granules to a 3-week old kitten. If a wormer has been started by a breeder, it is not necessary to continue with the same product. If the kitten has been imported, there is the possibility of infection with exotic parasites and the owner should be referred for veterinary advice.

Adverse effects (side effects) are rare with non-prescription wormers when used at the recommended doses in kittens. 

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 kitten accurately for each dose.
  • How often it should be used.
  • The expiry date.

Remind the owner to read the product information before use.

Practical exercise

Become familiar with your product range. Find out what products are for worming kittens. 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 cats and dogs. ESCCAP guideline 01 second edition. September 2010.

Fisher M. Toxocara cati: an underestimated zoonotic agent. Trends in Parasitology 2003; 9: 167-70.

Fisher M. Update on Toxocara spp. and toxocarosis. Companion Animal 2014; 9: 465-8.

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