Roundworms in cats are common intestinal parasites, particularly in kittens and cats that have access to the outdoors. The most common species is Toxocara cati, although Toxascaris leonina may also be present. In dogs, the situation is similar — see internal worming in dogs.
What do roundworms in cats look like?
Adult worms are elongated, cylindrical, white or cream-coloured, and may resemble thick threads or spaghetti. They may appear in the faeces or in vomit. The eggs are microscopic and cannot be seen with the naked eye.
How does a cat become infected?
- By ingesting eggs present in soil, sand, paws, fur or contaminated objects.
- By hunting small mammals or birds carrying larvae.
- Through their mother’s milk, in the case of kittens.
The eggs passed in the faeces need to mature in the environment. After that, they can remain in the soil for long periods.
Why it is necessary to repeat the worming treatment
This is the part that causes the most confusion: a worming treatment acts on the worms currently present in the gut. It does not provide protection against a new infection the following week, nor does it eliminate the eggs already spread throughout the environment.
There is a practical detail here that is worth its weight in gold. The eggs are not infectious the moment they are passed in the faeces — they need weeks in the environment to mature. In the case of the dog roundworm, Toxocara canis, the Merck Veterinary Manual states that it takes around 2 to 4 weeks for the egg to become infectious. This is precisely why removing faeces from the litter tray every day is so effective: it removes the eggs before they become a hazard. Cleaning the litter tray just once a week gives the eggs plenty of time to mature inside your home.
What are the signs?
Many adult cats show no symptoms. In kittens or in severe infections, the following may occur:
- a distended abdomen;
- poor growth or weight loss;
- dull coat;
- diarrhoea or vomiting;
- loss of appetite;
- visible worms;
- coughing whilst the larvae are migrating.
How is the diagnosis made?
Diagnosis usually involves microscopic examination of the faeces. In certain situations, antigen tests or molecular methods may be used. A single negative result does not always rule out infection, particularly if eggs have not yet been laid.
How often should deworming be carried out?
There is no one-size-fits-all schedule for all cats — it depends on their age and lifestyle. As a guide, the Merck Veterinary Manual describes the following schedule for kittens: treatment at 2 weeks of age, repeated every 2 weeks until 12 weeks, and then monthly until 6 months. The mother should be treated at the same time as the litter, as she can pass on larvae through her milk.
For adult cats, the same source indicates that the frequency should be based on a risk assessment of the animal’s environment: a cat that hunts and goes outdoors does not need the same treatment plan as a cat that lives indoors in a flat. It also recommends a faecal analysis at least once a year to confirm that the treatment plan is working.
These figures are general guidelines, not a prescription. It is the vet who determines the product, the dose and the interval, as they know your cat’s weight, age and medical history.
Treatment and prevention
Treatment should be determined by the vet based on your cat’s age, weight, clinical condition and risk. Do not use products intended for dogs on a cat: some substances can be toxic to cats.
To reduce the risk:
- remove faeces from the litter tray daily;
- wash the litter tray regularly;
- wash your hands after cleaning;
- keep children away from the litter tray;
- limit the consumption of game and avoid raw meat or offal;
- follow the parasite control programme and have the recommended faecal tests carried out.
You can find a range of cat litter and hygiene products, but no accessory can replace veterinary care.
What if the cat never leaves the house?
The risk is lower, but it’s not zero — and it’s a common mistake to assume that an indoor cat doesn’t need any preventative measures. The eggs are microscopic and hardy, and can enter the home in various ways: on the soles of shoes, in pots containing garden soil, or brought in by a second pet that goes outside.
There are also two scenarios that often go unnoticed: kittens born already infected via their mother, and indoor cats that catch prey that has entered the home — a bird that flew onto the balcony or a rodent. Therefore, even for an indoor cat, the decision on whether to treat for worms and how often remains with the vet, and is not something to be automatically overlooked.
Roundworms or tapeworms? They’re not the same thing
It’s worth distinguishing between them, as prevention differs. Roundworms are the long, cylindrical worms described above, which resemble spaghetti. Tapeworms (notably Dipylidium caninum) are flat and segmented: what you see around the anus or in the cat’s bedding are loose, small, whitish segments, resembling grains of rice or cucumber seeds.
The practical difference lies in how they’re transmitted: the most common tapeworm in cats is transmitted when the cat swallows an infected flea whilst grooming itself. In other words, if these segments appear, the problem cannot be resolved with an internal worming treatment alone — the fleas must also be treated, otherwise re-infection will occur. Always check with your vet to confirm which of the two you are dealing with, as the treatment is not the same.
Can roundworms in cats affect people?
Yes. Toxocara cati is of zoonotic importance. Human infection usually occurs through the accidental ingestion of eggs present in a contaminated environment, rather than through casual contact with the cat. We explore this further in ‘Should pet owners give their animals worming treatment?’. Hand hygiene and the prompt removal of faeces are important measures.
Children are the group most at risk, particularly in parks and outdoor litter trays, as they put their hands in their mouths more frequently. Washing hands after playing in the dirt and covering outdoor litter trays when they are not in use are simple measures that make a real difference.
When should you seek help straight away?
Contact your vet if your pet has repeated vomiting, severe diarrhoea, blood in the stools, a painful or very distended abdomen, dehydration, weakness, pale gums, persistent refusal to eat, or if a kitten has a lot of worms.
Sources
- ESCCAP — Toxocara infection
- Merck Veterinary Manual — roundworms in small animals
- CDC — human toxocariasis
Informative content, revised in August 2026. This is not a substitute for a veterinary consultation.