Worms in Cats & Dogs

Written by Shula Berg BVSc CertAVP(GSAS) GPAdvCert(SASTS) MRCVS
Clinically reviewed by Elizabeth McLennan-Green BVM&S CertAVP(SAM) MRCVS

- Overview
- Roundworms
- Symptoms
- Causes
- Treatment & Prevention
- Tapeworms
- Symptoms
- Causes
- Treatment & Prevention

Worms are parasites that live in the intestines of cats and dogs. They do not always cause obvious illness, but can cause vomiting, diarrhoea and weight loss. Some worms can also cause problems in humans, so it is important we prevent our pets becoming infected.

There are two types of worms we see commonly in cats and dogs:

Roundworms 

Roundworms are also known as nematodes or ascarids. They are called roundworms due to their shape and are often described as looking like pieces of spaghetti. Roundworms can grow very long, often 3-6 inches in length. They live within the intestines and feed off digested food.

Symptoms

Roundworms can cause:

Vomiting and diarrhoea
Poor growth
Pot-bellied appearance
Discomfort in the abdomen (tummy)
Reduced appetite
Dull coat

Symptoms are worse in young puppies and kittens, and severe infestations can even be fatal. In adult dogs and cats roundworms will not always cause symptoms, so a healthy appearance does not mean there is no infection.

How do pets get roundworm?

Roundworm infections are most commonly caught by ingesting faeces from an infected animal, such as grooming after walking through soil containing faeces, or sniffing another dogs faeces. They can also be spread to puppies and kittens through milk if the mum is infected. Some animals can carry roundworm eggs without being ill (known as an intermediate host), but will infect a cat or dog if they themselves are eaten.

Roundworms can also cause disease in people, especially the dog roundworm called Toxocara Canis. People are most commonly infected by ingesting tiny amounts of animal faeces. It is most common in small children, who may play in contaminated soil then put their hands in their mouth. Eggs are not infectious until 10-21 days after the animal passes them, so fresh faeces is less of a concern. Symptoms of roundworm infection in people can include cough, fever, stomach pain, weight loss, rashes and tiredness. Uncommonly, the parasites can affect the liver, brain or eyes, causing blindness or seizures.

Preventing and treating roundworm

Roundworms can be prevented by regular worming of cats and dogs, using an appropriate product. The frequency of treatment for adult animals is dependent on an individual patient's lifestyle, human interactions and daily activities. Frequent worming is advisable in young puppies and kittens until 6 months of age. Your vet team can advise on the best product and frequency for your pet.

Tapeworms 

Tapeworms are also known as cestodes. They are flat, segmented and can grow up to 30cm in length! Eventually the segments break off and are passed in faeces; they are about 1cm in size and are often described as looking like grains of rice. Tapeworms live within the intestines where they attach to the wall of the gut.

Symptoms

Tapeworms can cause:

Vomiting and diarrhoea
Weight loss
Stunted growth
Intestinal blockage
Irritation around the back end

Symptoms are worse in young puppies and kittens, and severe infestations can even be fatal. In adult dogs and cats tapeworms will not always cause symptoms, so a healthy appearance does not mean there is no infection.

How do pets get tapeworm?

Tapeworm infections are not passed directly between animals. Instead, the eggs must pass through an intermediate host (another animal that can pass the tapeworm without being ill). The most common tapeworm affecting pet dogs and cats is spread by fleas, which are swallowed during grooming. Less common tapeworms can be spread by rodents, rabbits and birds so are seen more in cats that hunt.

Preventing and treating tapeworm

Tapeworms in cats and dogs can be effectively prevented through regular worming and flea control. Your pet’s lifestyle and behaviour, such as hunting, scavenging, or close contact with other animals, play a key role in determining their risk of tapeworm infection. The frequency of treatment for adult pets should be tailored to their individual habits, environment, and interactions with people and other animals. Your vet team can help you choose the most suitable product and treatment schedule to keep your pet protected.

Full worming treatment is included in membership of The Healthy Pet Club.

Disclaimer

Please note that the content made available on this webpage is for general information purposes only. Whilst we try to ensure that at the time of writing all material is up to date and reflects industry standards, we make no representation, warranties or guarantees that the information made available is up to date, accurate or complete. Any reliance placed by yourselves is done so at your own risk.

Page last reviewed: 2^nd September 2025
Next review due: 2^nd September 2027