Although most owners prefer not to think about it, worms are a frequent problem in our pets. Most dogs will be affected at some time in their life, often more than once. The most common type of worms in dogs are intestinal worms. Other types of worms can affect the lungs and heart, and dogs that travel abroad are exposed to an even wider range of parasites.  Puppies and young dogs are much more likely than older dogs to have worms and to develop signs of illness because of them. Some canine worms can also cause problems in humans, especially young children.

What are the signs of an infestation?

Common signs of an intestinal worm infestation in your pet might include;

  • weight loss or, in puppies, reduced growth,
  • a pot-bellied appearance,
  • diarrhoea,
  • vomiting
  • chewing or rubbing around their bottoms due to irritation.

Occasionally affected pets will develop a mild cough. Severely affected puppies can become very unwell as they cannot absorb all of the nutrition they need due to the worms. In very large numbers, worms can sometimes cause an intestinal blockage that can be life threatening and requires urgent surgery.

Signs of an obstruction might include severe vomiting, loss of appetite and abdominal pain. Some pet owners notice worms in their dog’s stool or in vomit. However, this generally only happens when the pet has a very large infestation and shouldn’t be relied upon. Mildly infected dogs may show no signs at all. 

What worms are we talking about?

There are two main types of worm that infect the guts of dogs in the UK and these are:

Roundworms (Toxocara canis and Toxocara leonina)

These are thin, white and look typically worm shaped. They are a common problem in young dogs and puppies. Eggs from these worms are passed in faeces and live for a long time in the environment. They can occasionally be swallowed by children where they have the potential to cause serious problems including blindness. Roundworms can infect dogs if they hunt and eat rodents, or from eggs in the environment. Puppies can also be infected across the placenta and via their mother’s milk. This is why regular worming of pregnant and nursing bitches, as well as their pups is vital. It is important to note, not all products are safe for use in pregnancy and lactation so veterinary advice should be sought before treatment in these cases.  

Tapeworms (Echinococcus granulosus, Dipilydium caninum and Taenia species)

The second type of worms are called tapeworms and as the name suggests their shape resembles a flattened tape, which is made up of small segments.  Sometimes these small segments will be spotted either on bedding or around a pet’s bottom and resemble a grain of rice. Occasionally the Echinococcus tapeworm can infect people and cause dangerous cysts on internal organs. Tapeworms come from two main sources depending on their species – fleas and eating raw meat, rodents or carcasses.  Farm dogs are especially likely to be infected and should be wormed more regularly.

Heart and lungworms

There are several species of lungworm that affect dogs in the UK.  The most important of these is Angiostrongylus vasorum. Dog’s who are infected with this lungworm initially show signs of coughing, lethargy and sometimes difficulty breathing. In some cases the parasite can cause a problem with blood clotting. Affected pets may bruise more easily, suffer nosebleeds or unusual bleeding from elsewhere, and in the worst cases the condition can be life threatening. This form of lungworm is spread by slugs and snails. It is more common in younger dogs partly due to their curiosity and the likelihood of them ingesting these creatures.  Other forms of lungworm tend to cause milder disease – mainly coughing or even no signs at all. 

Treating and preventing worms

Many different worming products are available to treat worm infestations. However, not all products are effective against all worms so it is really important to select the right product at the right time. Worms such as tapeworms and lungworms often need very specific products to treat infestations. Oral wormers (eg tablets, liquid or pastes) often have little or no residual activity. This means they will kill or remove worms that are present at the time of treatment, but provide no ongoing protection so pets need treating regularly according to their level of risk. 

Herbal and homeopathic remedies, as well other “natural wormers” e.g. feeding rabbit ears, are not effective at treating worms and leave dogs at risk of severe infestation and illness. Practising good hygiene by picking up dog faeces, regular flea treatment and preventing hunting and scavenging will all reduce the likelihood of your dog being infected. If in doubt contact your veterinary practice for advice about the best worming regimen for your pet.

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