When to see a vet urgently
Seek urgent care if your cat develops any of the following:
- repeated vomiting with an obviously painful or swollen abdomen;
- difficulty breathing or marked breathing effort;
- collapse, unusual weakness or very pale gums and other mucous membranes;
- rapid deterioration in a kitten, with refusal to eat and severe diarrhoea.
Do not assume that parasites alone explain the symptoms. You can find a vet near you.
Overview
Roundworms are white or yellowish, round-bodied parasites up to 10 cm long that live in a cat's small intestine. They feed on the intestinal contents and physically damage the lining, causing inflammation and digestive problems. In a heavy infection, worms can form clumps that block the intestine, causing an intestinal obstruction. Larval migration through the body is also dangerous: larvae can damage the lungs and liver.
Larval migration does not mean that every infected cat develops liver disease. Clinically significant liver damage is rare in this situation. An adult cat may remain symptom-free while shedding eggs into the environment.
Roundworms do not attach to the intestinal wall in the same way as blood-feeding hookworms. Hookworms can also cause intestinal symptoms, but they are different parasites. Cats can carry Toxascaris leonina as well as Toxocara cati. These species have different life cycles, so worm infections in dogs and cats cannot all be treated as the same condition.
Causes of infection
Cats can acquire roundworms in several ways:
- swallowing eggs from the environment, including soil, sand and contaminated objects;
- eating rodents and birds that act as transport hosts (paratenic hosts), with larvae in their tissues;
- kittens acquiring infection through their mother's milk;
- direct contact with infected animals.
Infection does not usually pass simply through being beside another animal. A cat must swallow an infective egg or tissue containing larvae; milk can also transmit infection to a kitten. In a shared environment, animal contact and exposure to faeces may occur together. Toxocara cati in cats does not normally cross the placenta in the same way as Toxocara canis in dogs.
An egg passed in faeces is not immediately infective. The larva must first develop inside the egg in the environment. Prompt removal of faeces therefore reduces the chance of infective eggs building up. Invisible eggs can remain in soil even after the faeces have broken down.
Roundworm eggs remain viable in soil for several years.
Risk factors
- kittens, especially those under six months old;
- cats that go outdoors;
- hunting cats that eat rodents;
- animals without regular parasite control;
- poor hygiene conditions.
Age particularly affects how likely an infection is to cause symptoms. Adult cats are not completely protected against infection either. A cat that eats prey has different exposure from an indoor cat that does not eat raw meat. Prevention is assessed against these actual exposures, rather than simply whether your cat has previously appeared healthy.
A faecal study from northern Europe published in 2024 found relatively few intestinal parasites in pet cats but considerably more in rescue cats. Toxocara cati was among the parasites found in pet cats in the study. The animals were over six months old, so the findings do not directly describe infections in young kittens. One study cannot establish that an indoor cat never needs parasite testing.
Symptoms
Symptoms vary with the worm burden:
- in kittens: a pot belly, tiredness, slow growth and a dull coat;
- vomiting, sometimes with visible worms;
- diarrhoea or alternating constipation and diarrhoea;
- reduced appetite and weight loss;
- coughing and difficulty breathing as larvae pass through the lungs;
- anaemia and wasting in severe cases.
A list of symptoms alone cannot confirm a parasitic infection. A pot belly and slow growth can be associated with roundworms, but diarrhoea, vomiting and weight loss have other causes too. Anaemia also needs separate investigation; pallor or weakness is not always caused by ascariasis.
A visible worm in vomit or faeces is a useful observation for your vet. However, the absence of worms in faeces examined with the naked eye does not rule out infection. The eggs are microscopic, and a lack of symptoms does not confirm that your cat is not shedding them.
Possible complications
A heavy parasitic infection can cause serious complications:
- intestinal obstruction;
- intestinal inflammation and severe diarrhoea with dehydration;
- damage to the liver and lungs from larvae;
- physical weakness and reduced immune defences;
- a zoonotic risk to people, particularly children: Toxocara cati can cause visceral or ocular toxocariasis.
People usually acquire toxocariasis by swallowing eggs that have become infective in the environment. The main risk involves faecally contaminated soil and material transferred from hands to the mouth. This does not mean that every contact with a cat causes infection. Protect children by preventing them from eating soil and ensuring that they wash their hands.
In people, larvae can migrate into tissues and the eye. Different professionals assess illness in cats and people: your vet treats your cat's infection, while you should discuss any symptoms of your own with a healthcare professional. Cat worming medicine must not be used to treat people.
Diagnosis at the vet
Diagnosis is based on:
- a faecal sample, examined microscopically for eggs;
- a clinical examination and history;
- imaging, such as ultrasound or X-rays, when needed to assess complications.
During faecal testing, eggs are separated from the sample and identified under a microscope. The result detects an egg-producing infection. Early in infection, however, a cat may have developing parasites that are not yet shedding eggs. A negative egg test alone therefore cannot rule out infection in every situation.
Some laboratories also use faecal parasite antigen or PCR tests. An antigen is an identifiable substance produced by the parasite, while PCR looks for its genetic material. These tests can complement microscopy, for example when there are few eggs or they are not yet being produced. Your vet chooses the appropriate test based on symptoms and exposure.
Tell your vet about hunting, diet, previous parasite findings and any parasite treatments given. For a kitten, information about infections in the mother and littermates can also help. Ask the laboratory or veterinary practice for sampling instructions. Examination of a cat with severe symptoms should not be delayed to collect a sample.
Treatment and monitoring recovery
Effective medicines are available for roundworm infection. The choice depends on your cat's age, weight and health, and on which parasites need treatment. Parasite medicines do not all cover the same species or developmental stages. Use only a product suitable for cats, following your vet's instructions.
When treating a kitten or a cat with severe symptoms, your vet also assesses hydration, nutrition and other possible illnesses. Suspected intestinal obstruction requires examination; giving a wormer at home cannot replace this. Your vet also decides whether a follow-up sample or repeat treatment is needed.
Make sure the medicine is successfully given as instructed. If your cat vomits it, administration fails or symptoms continue, ask the practice for further advice. Do not double the dose or switch products yourself. Continuing diarrhoea does not automatically indicate drug resistance, as re-exposure or another illness may be responsible.
Monitor a kitten's growth, appetite, activity and stool quality. In an adult cat, weight trends can help reveal a persistent problem. Successful treatment does not give permanent protection: your cat can become infected again from the same prey animals or contaminated environment. Treatment and reducing exposure therefore go together.
Prevention
Preventing ascariasis is straightforward and effective:
- regular parasite control as advised by your vet;
- parasite treatment for kittens from an early age;
- good hygiene, including washing hands after handling animals or the litter tray;
- preventing hunting and eating raw meat;
- keeping your home and the litter tray clean.
The prevention plan is tailored to the individual. It takes account of outdoor access, hunting, raw feeding, previous infections and household members, particularly young children. Parasite control for a kitten and its nursing mother is planned together. Testing and treatment intervals depend on your vet's risk assessment.
Remove faeces from the litter tray promptly and clear droppings from outdoor areas too. Ordinary disinfectants do not reliably destroy hardy roundworm eggs, making physical removal of visible dirt essential. Do not try to replace cleaning with strong chemicals that could harm your cat.
Keep children's sandpits protected from animal faeces and teach handwashing after outdoor play and before meals. Limit hunting and avoid feeding uncooked meat or offal. These measures reduce both your cat's re-exposure and environmental contamination.
This text provides general information and does not replace veterinary care. Contact your vet if your cat develops symptoms.
Frequently asked questions
Can a cat without symptoms have roundworms?
Yes. Adult cats in particular can carry parasites and shed eggs without obvious illness. Testing and prevention are therefore assessed using lifestyle and previous infections too.
Is one negative faecal sample enough?
Not in every situation. Developing parasites may not yet produce eggs. Your vet may recommend repeat testing or an additional test method if symptoms and exposure give grounds for suspicion.
Can people catch roundworms by stroking a cat?
Toxocariasis requires infective eggs to enter the mouth. Prompt removal of faeces, handwashing and protecting children from contaminated soil are key preventive measures. Simply being near a cat is not the same as this route of infection.
This article is for general information only and is not a guide to treatment. If you notice the first signs of illness, contact your vet.
Paw4care editorial team
Sources
- Ascarid, Companion Animal Parasite Council, accessed 2026-11-05.
- Worm Control in Dogs and Cats: Guideline 01, Seventh Edition, June 2025, ESCCAP, accessed 2026-11-05.
- Toxocara cati – Learn About Parasites, University of Saskatchewan, accessed 2026-11-05.
- Low intestinal parasite prevalence in Finnish pet dogs and cats, Acta Veterinaria Scandinavica, accessed 2026-11-05.
- Gastrointestinal Parasites of Cats, Merck Veterinary Manual, accessed 2026-11-05.
- Gastrointestinal Parasites of Cats, Cornell University College of Veterinary Medicine, accessed 2026-11-05.
- Initial Triage and Resuscitation of Small Animal Emergency Patients, Merck Veterinary Manual, accessed 2026-11-05.