It can be alarming to discover that your cat has worms but it should not come as a surprise. All pets are affected at some stage in their life and many will be re-infected unless they are given regular, routine worming treatment. Except in rare cases, worms are unlikely to cause serious harm. Getting rid of worms is relatively simple and inexpensive so regular treatment is strongly recommended, particularly as some types of worm can be passed on to humans.

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What kind of worms do cats suffer from?

There are two important types of parasitic worm in cats – roundworms and tapeworms. Roundworms can grow up to 15 cm long and are white in colour. As their name suggests they are round (like string) whereas tapeworms are flat (like ribbons). Tapeworms can grow up to 60 cm long.

Both roundworms and tapeworms live in the cat’s intestines along with two other types of smaller worm, similar to roundworms, called whipworms and hookworms. These only rarely affect cats in the Ireland.

What damage do worms cause?

Intestinal worms help themselves to your cat’s food and can damage the gut causing loss of blood. Worms can also cause diarrhoea, dehydration and anaemia, and this may make your cat run-down and susceptible to other diseases. If there are a lot of worms your cat may cough, lose weight, have a rough, dry coat or a ‘pot-bellied’ appearance.

In kittens a worm infection can be serious, causing poor growth and sometimes, even death. If there are large numbers of worms the intestine can become blocked (although this is rare in an adult cat) and this may be fatal.

How are worms passed on?

Roundworms grow in the intestine laying thousands of eggs which pass out in the faeces. The eggs can survive for months or even years in the soil and need to lie in the environment for some time before they can infect another animal. They find their way into a new host either directly, when eaten by a cat or indirectly after being swallowed by a rodent which then is eaten by the cat.

Inside the rodent – and sometimes in people – the egg hatches inside the gut, burrows through the intestine wall and lodges as a resting larval stage somewhere within the body. Immature worms also survive in the tissues of an infected cat. If that cat is female and has kittens they make their way to the cat’s breast and are passed to the kittens in the milk.

Tapeworms are anchored by their head to the intestine wall and grow a continuous ribbon of segments, each packed with eggs. The segments gradually break off and are passed out of the cat’s anus. They may wriggle like a maggot for a short time and then dry up (sometimes still attached to your cat’s fur).

The most common type of tapeworm re-infects your cat by way of fleas. Immature fleas live in the environment and eat a variety of solid food including cat faeces and tapeworm eggs. The next cat will become infected when it swallows an adult flea whilst grooming itself. There is also a less common type of tapeworm which uses mice and other rodents to complete its life cycle.

The eggs passed out in the cat’s faeces are eaten by the rodent and form inactive cysts in muscle or other organs. Your cat is then infected when it hunts and eats the rodent.

How can I tell if my cat has worms?

Apart from the general effects on health described above, signs of infestation are to be found in your cat’s faeces. Segments of tapeworm looking like grains of rice can often be seen in the faecesor in the fur around your cat’s rear end. You may be startled to see them move. Roundworm eggs can only be seen by using a microscope.

How can worms be destroyed?

There are some highly effective treatments which will kill worms. These are available as liquids, tablets or ‘spot-ons’. However, not all the products are equally good and some work against certain types of worms and not others. Your vet will be able to advise you on which product is best for your cat.

Worms are so common that it is safe to assume that any kitten, cat with fleas, or animal which regularly catches rodents will be infected. Kittens should be dosed every two weeks from four weeks to 24 weeks of age and older cats should be treated about every three months. Some cats, e.g. cats that hunt, will need more regular treatment than others. You should discuss with your vet the most appropriate treatment regime for your pet.

Can I or my family or I be affected?

The common roundworm found in dogs is a rare but potentially serious cause of human disease. The larval stages burrow through the gut wall and become embedded somewhere within the body and can cause serious damage if they end up, for example, in the eye.

There are occasional reports of the victim, usually a child, being blinded in one eye. However, the type of roundworm normally found in cats is much less likely to cause problems in humans and most of the parasites found in cats are unable to survive at all in people.

What can I do to reduce the risk?

Apart from regularly worming your pets, there are a number of other measures which can stop worms being passed on from cat to cat – or from cat to people. If a cat uses your garden as a toilet clean up the faeces and bury them (if your cat has not done so already) or put them inside a sealed bag in your dustbin.

If your cat normally uses a litter tray, remove the faeces every day and disinfect the tray every week using hot water. Check your cat for signs of fleas and treat them regularly using the product recommended by your vet. Fleas are more numerous during summer and autumn. Discourage your cat from hunting rodents by keeping it indoors at night. Children will put dirty fingers and other objects into their mouths and this may bring them into contact with worm eggs.

Make sure that they wash their hands after playing in a garden or other open areas which may be used as a toilet by cats. Remember the greatest risk of children being infected with worms is from other children not your cat.