Worms in Dogs and Cats

Worms are internal parasites and numerous species affect dogs and cats. They occur in a variety of organs, including lungs, heart, blood vessels, kidney, eye, but mainly in the bowel. The most common worms are classed into two main groups; roundworms and tapeworm that live in the bowel. Although quite common, worms rarely cause serious disease. Infected pets are a source of infection to other pets and people.


These include ascarids, hookworms and whipworms.

a) Ascarid (also called roundworms) infections are extremely common, and it is safe to assume that all puppies are infected. Heavy infections are most common in kennels and catteries especially under conditions of poor hygiene. Bitches can infect puppies in the womb, through milk or saliva. Whole litters of puppies can die within 2 to 3 weeks of age as a result of lung and bowel damage. In less severe cases, puppies and kittens are generally unthrifty, pot bellied, have intermittent diarrhoea and possibly anaemia. Roundworms produce microscopic eggs which are shed in the faeces of infected pets and are a source of infection to other pets and humans. Pets can also be infected by eating an infected animal, such as a mouse or rat, which has eaten eggs. Roundworms are short, white and rounded bodied and are sometimes seen when passed by or vomited by infected puppies. Toxacariasis (also called Visceral Larval Migrans) is a serious disease which occurs in humans as a result of infection with these worms, and young children are most susceptible.

b) Hookworm infection occurs frequently during the summer, particularly in dogs confined to small areas of wet ground such as dog runs. The main signs of disease are anaemia, stunted growth, skin disease and weakness. Puppies are most severely affected and infection can occur in the womb or during nursing. Heavy infections also occurs in cats and are associated with recurrent diarrhoea, poor growth and a poor coat. Cutaneous Larval Migrans is a human skin condition resulting from hookworm infection.

(c)  Whipworms infect many dogs but in most cases the number of worms involved causes little apparent disease. However, severe infections are not uncommon, particularly in dogs up to 18 months old. The signs are of profuse diarrhoea, weight loss, lack of thrive and death. Whipworm infection in cats has not been reported in Ireland.


Three types of tapeworm affect dogs and cats. The most common type occurs on flea infested pets which have swallowed a flea infected with a tapeworm cyst. The other types are picked up by eating raw flesh or meat from infected animals. In most cases treatment is only effective if the pet is properly treated for fleas. Tapeworms are long flat worms composed of many individual segments whereas whereas tapeworms release mature segments (which again contain eggs) from the end of the worm into the faeces. These segments sometimes look like grains of rice and are mobile. They can occasionally be seen on the hair around the anus of the cat or in the faeces.

Lung Worm in Cats

These live in the small airways of the lungs. Cats become infected by eating infected snails or other animals which have eaten infected snails, such as rodents, frogs or birds. Infection is common, but signs of disease are rare. The main signs are coughing, breathing difficulty and weight loss.


Laboratory examination of your pet’s stool is the best way of determining if and what types of worms it has, although tapeworm eggs are rarely found in the stool.


If your pet has been diagnosed as having worms an appropriate treatment should be given. Otherwise, all pets should be treated regularly for worms every 3 months. It is very important to use an effective treatment at that the correct dosage.Many over-the-counter and pet shop worm treatments are not effective. Most treatment is given on a weight basis so it is helpful if you know your pet’s weight before treatment.

As puppies can be infected with roundworms from a very young age it is important that worming is started early and repeated regularly. Tapeworms are more likely to be a problem in adult cats and at this age less frequent but still regular worming is required.

A suitable protocol for worming cats of all ages is

Puppies & Kittens: Treat for roundworm weekly from 4 weeks to 6 months of age.

Dogs & Cats: Routine treatment every 3 months.

Pregnant Bitches: Treat for worms before mating. It is also important to treat her for roundworms during pregnancy and when nursing the puppies.

All Animals: Check regularly for fleas and treat if necessary. Do not allow your pet to eat raw flesh or meat. Clean up dog and cat stool from your garden, yard, or kennels, etc.

Puppies from 4 to 16 weeks of age
Treat every two weeks with a product active against roundworms, e.g. pyrantel.

Dogs from 6 months of age and older
Treat every two to six months

Public Health

To reduce the possibility of human infection with worms, pet owners should worm their pets regularly and make sure that dogs in particular do not soil in public areas, such as streets, or parks. If this should happen the onus is on you, the owner, to remove and dispose of it safely.

Due to the potential human health hazard, as well as the possible ill-health to the cat, regular worming of cats is important. In addition, careful disposal of litter from litter trays is important, and ideally the tray should be disinfected weekly with boiling water.

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