Pet Factsheets

Deworming your dog

It can be alarming to discover that your dog 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 deworming 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 onto humans.

Echinococcus granulosus: adult ©Sheelagh Lloyd

There are two important types of parasitic worm in dogs – roundworms and tapeworms. Roundworms can grow up to 15 cm long and are white in color. 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 dog’s intestines along with two other types of smaller worm (similar to roundworms) called whipworms and hookworms. However, these rarely affect dogs in the UK. In some countries there are parasitic worms that can live in the dog’s lungs, heart, stomach or bladder but these are rarely seen in Europe.

Intestinal worms help themselves to your dog’s food and can damage the gut causing loss of blood. Worms can also cause diarrhea, dehydration and anemia, and this may make your dog run-down and susceptible to other diseases. If there are a lot of worms your dog may cough, lose weight, have a rough, dry coat or a ‘pot-bellied’ appearance. In puppies a worm infection can be more 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 dog) and this may be fatal.

Roundworms grow in the intestine laying thousands of eggs which pass out in the feces (droppings). 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 dog) or indirectly, (after being swallowed by a rodent which is then eaten by the dog). Immature worms also survive in the tissues of an infected dog. Immature worms can be passed from a mother to her puppies 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 in the feces. These segments look like grains of rice and many wriggle like a maggot for a short time before they dry up (sometimes still attached to your dog’s fur). The most common type of tapeworm moves on to a new dog by way of fleas. Immature fleas pick up infection from dog feces in the environment and dogs are then infected if they accidentally swallow an adult flea during grooming. There is also a less common type of tapeworm which uses mice, other rodents and rabbits to complete its life-cycle. This parasite lies dormant in the muscle or other organs of a small rodent or rabbit and dogs are infected if they eat these animals.

Apart from the general effects on health described above, signs of infestation are to be found in your dog’s feces (droppings). Puppies may vomit or pass round worms (looking like string) in their feces. Segments of tapeworm (looking like grains of rice), can often be seen in the feces or in the fur around the tail base and back legs. Roundworm eggs can only be seen by using a microscope to examine the feces.

There are some highly effective treatments which will kill worms. These are available as liquids, pastes, tablets or powder. 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 dog. Worms are so common that it is safe to assume that all puppies, dogs with fleas, and animals which regularly catch wildlife will be infected. Puppies should be treated with dewormers every two weeks, from four weeks to 16 weeks of age, and older dogs should be treated about every three months. You should discuss with your vet the most appropriate treatment regime for your pet.

The common roundworm found in dogs is a rare but potentially serious cause of human disease. The larval stages of this worm 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.

Apart from regularly deworming your pets, there are a number of other measures which can stop worms being passed on from dog to dog, or from dog to people.

• If your dog uses your garden as a toilet, clean up the feces and bury them or put them inside a sealed bag in your dustbin.
• Check your dog for signs of fleas and treat them regularly using the product recommended by your vet. Fleas are more numerous during summer and autumn, although will survive all year round in centrally heated homes.
• 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 any open areas which may have been used as a toilet by dogs. Remember the greatest risk of children being infected with worms is from other children, not your dog.