Parasiticides for cats and dogs: a rational approach. Module 4. Kitten worming

Why we are doing this module

The cat roundworm Toxocara cati is an intestinal nematode with ubiquitous presence in the UK.  It can cause significant disease in kittens and can be transmitted to humans to cause toxocariasis, an important zoonosis. Roundworm control is the most important consideration in kitten parasite management.

There is no strict definition of the term roundworm. In these modules we use it for ascarids, which include dog and cat roundworm (Toxocara spp.), hookworm and whipworm. T. cati is commonly known as the cat roundworm.

Adult worms live in the small intestine and shed eggs into the environment via the faeces of infected cats. When first shed the eggs are unembryonated and are not infective, so fresh faeces do not present a zoonotic risk. Ingestion of eggs that have developed to the embryonated stage is needed for infection, a process that takes 3-4 weeks at room temperature, longer at cooler temperatures (Fisher 2003).

Although cats may be infected by ingesting embryonated eggs or infected paratenic hosts, the most common route of infection in kittens is transmammary (Overgauuw & van Knapen 2013). This can result in a high prevalence of T. canis infection in kittens not treated with an endoparasiticide.

In lactating queens, infective larvae may be passed to kittens during suckling. These develop to adulthood in the intestine. If embryonated eggs are ingested from the environment, larvae released from the eggs cross the gut wall and migrate to the lungs via the liver. Once in the lungs the larvae migrate to the trachea, are coughed up, swallowed and complete development to adult worms in the small intestine.

In older kittens and adult cats the larvae that hatch from ingested eggs are more likely to migrate to various tissues including the liver, central nervous system, lungs, heart and muscle, where they encyst and can remain dormant for years (Overgauuw & van Knappen 2013). At any time, some of the dormant larvae may reactivate, migrate back to the gut, complete development to adults and start producing eggs. In kittens over 3 months old, the liver-lung pathway for larval migration is thought to become less likely and tissue migration more likely. Larvae ingested through consumption of a paratenic host do not migrate but continue their development to adulthood in the gut.

Roundworm infection in kittens may be subclinical or may lead to mild signs such as a pot-bellied appearance and transient cough. High exposure to infection via embryonated eggs in the environment from infected queens or litter mates can lead to significant migration of larvae to the lungs and severe respiratory signs. It is thought that the lung damage caused by the migration of larvae to the lungs might contribute to feline bronchitic syndromes (Dillon et al 2013). Kittens infected with high numbers of worms may present with lethargy, poor weight gain and failure to thrive. Severe infections in young kittens can result in sudden death at a few days of age due to intestinal obstruction or intussusception.

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. After ingestion, hatched larvae penetrate the small intestine wall and are carried in the circulation to the liver where they may lodge and cause a granulomatous response. Some migrate to other tissues, including the lungs, striated muscle, heart, brain and eye. Infection is usually asymptomatic and the larvae die without causing serious problems. But there can be generalised symptoms (such as fever and urticaria), eosinophilia and focal signs related to the migration of larvae (such as bronchospasm or granulomatous swelling in the eye) and occasionally death due to heart or brain involvement. Rarely, larvae survive in the tissues for years, causing symptoms long after the initial infection.

Some people are more vulnerable than others to infection: young children are more likely than others to accidentally ingest infective eggs; people who are immunosuppressed might be at increased risk of infection.

Good hygiene and reducing environmental contamination with Toxocara eggs are central to the control of human toxocariasis. Although there are many sources of environmental contamination with Toxocara spp eggs, the contribution from cats infected with T. cati is thought to be significant (Fisher 2003). Toxocara spp eggs are very resistant to adverse environmental conditions and can survive in the environment for years. There is no practical way of reducing the number of eggs in the environment once they are present, and removal of cat faeces is impractical,  so deworming cats is key to controlling T. cati.

The zoonotic potential of T. cati, its ubiquitous presence and the potential for disease associated with high worm burdens, make roundworm the key parasite to consider in kittens. The aims of deworming kittens are to prevent disease in the kittens and to suppress T. cati egg output.

ESCCAP guidelines recommend that kittens are dewormed at 3 weeks of age and then every 2 weeks until 2 weeks after weaning and then monthly until they are 6 months old (ESCCAP guideline 2010). The later starting age for the treatment of kittens (at 3 weeks) compared with puppies (2 weeks) is because kittens, unlike puppies, do not become infected before birth. The pre-patent period (the time taken for infective eggs to develop into egg-producing adults) of T. cati in adult cats is around 8 weeks, (Fisher 2014) and so deworming every 4 weeks is expected to prevent most patent feline roundworm infections. However, as the transmammary route of Toxocara infection can produce patent infection every 2-3 weeks,  deworming every 2 weeks in young kittens is recommended. (ESCCAP guidelines 2010)

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. (ESCCAP guidelines 2010) One product (Profender spot-on, which contains emodepside + praziquantel) is authorised for the treatment of queens in late pregnancy to prevent lactogenic transmission to the kittens.

Kittens may be infected through the oral ingestion of eggs from other common types of roundworm such as Ancylostoma tubaeforme and Toxascaris leonine. These worms have no zoonotic potential and regular deworming to control T. cati should be sufficient to control clinical signs caused by these other roundworms.

Drugs that are active against roundworm*

benzimidazoles (febantel, fenbendazole)


macrocyclic lactones (eprinomectin, milbemycin, moxidectin, selamectin)



tetrahydropyrimidines (oxantel, pyrantel)

*check the SPCs for authorised uses of commercial products.

Any parasiticide product licensed for the control of an endoparasite infection (including with Toxocara spp) must have been shown in clinical trials to reduce adult worm counts by at least 90% (for more on this, see Module 1). On this basis, use of any product licensed for the treatment of adult roundworm in kittens at the recommended frequency can be expected to prevent levels of infection likely to cause significant disease. Deworming kittens initially every 2 weeks and then every 4 weeks after weaning will be sufficient to suppress patent infection. The Parasiticide Guide will show you all the UK products authorised for control of roundworm in cats, together with the minimum age and weight for which the products are authorised.

The authorised indications of most worming products for cats specify that they are active against adult T. cati worms. In contrast, the indications for a few newer products (spot-on solutions containing moxidectin + imidacloprid; eprinomectin + fipronil + S-methoprene + praziquantel; emodepside + praziquantel) specify activity against larval stages as well as adult T. cati worms. At present the relevance of these differences to the comparative efficacy of products in the control of T. cati is not clear. In practice the correct and regular use of products by the owner are probably more important factors.

The summaries of product characteristics (SPCs) of endoparasiticides authorised for use in kittens indicate that adverse effects are rare when the products are used at the recommended doses. The benzimadazoles (febantel and fendendazole) can cause self-limiting gastrointestinal signs. Macrocyclic lactones (such as milbemycin, moxidectin and selamectin) can rarely cause systemic neurological signs (tremors, ataxia) and gastrointestinal upset. To give the correct dose it is essential to weigh the kitten accurately for each dose.

When deciding which product is appropriate, there are several points to consider:

  • Choice of formulation –  Products are available as tablets, liquids, granules and spot-ons. If the client is going to be administering the product, it is worth asking which type of formulation they prefer because this might affect compliance. For example, a client might find it difficult to comply with a need for frequent dosing or be put off a particular formulation because of a previous experience of an adverse reaction to a product. There is no need to continue with the same dewormer used by a breeder or other vet.
  • A need to treat and prevent other parasite diseases – It is appropriate to consider other parasites that might affect kittens, such as fleas and ear mites. The required coverage can be achieved with a single product or a combination of products. Search the Parasiticide Guide to see what’s available. If a combination product is used, it’s important to consider if the treatment frequency needed for roundworm is too frequent for other parasites, in which case separate products might be more suitable.
  • Specific licence claims – Treatments for T. cati are likely to control other intestinal roundworms but if a breeding establishment is known to have other roundworms present in the environment such as Ancylostoma tubaeforme or Toxascaris leonine then products authorised for control of these nematodes should be used.
  • Cost –  The product(s) should be affordable to the client throughout the treatment period. Some products such as kitten suspensions are more economical for treating large numbers of kittens. Combination products may be more economical for treating several parasites in a kitten.  


If you prefer, you can listen to the whole audio presetation of puppy worming module using the following podcast. Don't forget that you can also download the podcast to your iPod, music player, tablet or smartphone using the Download link on the right of the audio player.

Goal of activity: Update knowledge; help clinical decision-making

Authors/disclosures: Veterinary Prescriber editorial team/no conflict of interest

Specific learning objectives: to improve knowledge and understanding of the use of parasiticides in cats and dogs.

Click the button below when you are ready to answer the CPD questions based on the parasiticides for cats and dogs module from Veterinary Prescriber.

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Some of the following CPD questions make use of our Parasiticide Guide. You may wish to use this link to open the guide in a new window now before attempting the questions.

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Dillon AR et al. Lung histopathology, radiography, high-resolution computed tomography, and bronchio-alveolar lavage cytology are altered by Toxocara cati infection in cats and is independent of development of adult intestinal parasites. Veterinary Parasitology. 2013; 193: 423-26.

ESCCAP. Worm control in cats and dogs. ESCCAP guideline 01 second edition. September 2010.

Fisher M (2003) Toxocara cati: an underestimated zoonotic agent. Trends in Parasitology 19: 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.