Dogs are, sadly, subject to a wide variety of unpleasant parasitic worms. These can cause weight loss, diarrhoea, stomach upsets, and even anaemia, liver or brain and eye disease in some cases. However, worms in the gut aren’t the only issue – lungworm is an increasing issue across the UK and Ireland. This worm causes difficulty breathing, blood clotting problems and may result in heart failure as well.

It is vitally important that we control these parasites, in order to keep our pets (and our families!) safe. However, to do so, we need to understand their life cycles.

We can divide the worms we commonly see into three groups:

Gut roundworms

These are worms like Toxocara and Toxascaris, and are fat, round worms (hence the name!) that live in the intestines of our pets. Dogs may be infected by swallowing the larvae passed in the faeces of other dogs, and in some cases, may be infected through their mother’s milk or even across the placenta while in the womb. Once inside, the larvae burrow into the gut wall; some species then return straight to the gut and start breeding, but others go on long migrations around the body, sometimes causing damage to all sorts of internal organs in the process. These worms are potentially transmissible to humans, especially children! Eventually, they return to the gut, breed, and start churning out little larvae to infect other animals.

These beasties most commonly cause weight loss (because they’re eating the dog’s food), sometimes diarrhoea and occasionally vomiting; while small numbers may not be noticeable, the more worms there are, the more severe the symptoms.

Gut tapeworms

There are a number of different tapeworms, but the most common one is Dipylidium caninum. This is spread by fleas (and, rarely, lice), and is really, really common! Most wormers won’t kill this worm – there’s only one active ingredient that works, called praziquantel, which is incorporated into most worming tablets nowadays. However, almost no spot-on products for dogs will kill this worm, which fastens to the gut wall and grows longer and longer. Sadly, with global warming, fleas are now a menace all year round, so we are seeing more and more tapeworm infestations.

The symptoms may be similar to the roundworms (it eats the dog’s food and irritates the gut wall), but often also include an itchy bottom. This is because the individual segments of the tapeworm, when pregnant, break off and crawl out of the dog’s bottom to release their eggs… something that can drive dogs wild!


There’s a lot of public awareness about this worm nowadays, as one drug company has launched a major publicity drive about it. The worms live in the blood vessels of the heart and lungs, and the larvae crawl out into the lungs, are coughed up, swallowed and then passed in the faeces. Dogs become infected by licking or eating a slug, snail, or any of the slime that these molluscs pass.

The symptoms may include breathlessness, blue gums, collapse, heart failure, abnormal bleeding, and often are fatal if untreated. Unfortunately, there are only a handful of drugs available to kill these worms and prevent a fatal infection.

So, how often do I need to worm my dog?

Many vets recommend worming an adult dog every 3 months. There are a number of spot-on products (containing moxidectin and imidacloprid) that will kill roundworms and lungworms, but they don’t kill tapeworms. There are also tablets (containing febantel and praziquantel) that will kill roundworms and tapeworms, but not lungworms.

However, there is now a prescription-only tablet (containing milbemycin and praziquantel) that, if given monthly, kills all three types of worms, preventing infection with roundworms, tapeworms and lungworm.

We strongly advise, therefore, that you worm monthly with this product to protect your pet from all corners. Pop in and see us for more details!