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Understanding the Different Types of Worms which can Affect Dogs and How to De-worm your Dog


This article is intended as a guide only; always follow the advice of your Veterinarian.

Worm infestations are very common in dogs and can cause distress and ill health. The most common are roundworms and tapeworms. With the exception of tapeworms, segments of which can be seen without magnification in the droppings, the best way to diagnose worms in your dog is to have your veterinarian perform a faecal exam. Your veterinarian will examine your dog's faeces under a microscope for the presence of microscopic worm eggs. However, your dog may have worms, yet show no eggs in the stool. This is why regular de-worming is so important.

Common types of worm

Roundworms (Toxocara canis, Toxascaris leonina)

Roundworms (or Ascarids) look like short lengths of spaghetti (around 4 inches in length), curled up into a coil. The adult worms live in the intestines of the dog, feeding on its contents.  Symptoms include a dull coat, lethargy, diarrhoea, vomiting and weight loss. The dog will be undernourished as the worms steal the majority of nutrients the dog consumes. In the adult dog, the worm larvae migrate into the body and form cysts in the muscles. There they may lay dormant for years, only to be activated in times of stress. The most common time of awakening is during pregnancy, when large numbers of worm larvae migrate into the puppy in the uterus, infecting it before it is even born.

The most common roundworm to infect dogs in the UK is Toxocara canis which can also infect humans. Children are particularly vulnerable as they may pick up the worm eggs from contaminated soil while playing. The worm larvae migrate through the child’s body, and can sometimes end up behind the retina where they can cause permanent damage to the child’s eyesight. Worms have also been implicated in epilepsy.

Hookworms (Ancylostoma caninium)

Like Roundworm, Hookworm lives in the intestines and can also be transmitted to humans. Hookworms can affect a dog at any age. They are small, thin worms that hook on to the intestinal wall and sucks the blood from their victims, causing anaemia and in severe cases, death. Due to their sharp teeth, they also cause bleeding in the intestines. Hookworms are not visible by the naked eye, therefore should be diagnosed by a vet. As with roundworm, hookworms also live and grow to adulthood in the intestines. They can also be transmitted to pups while in the mother’s uterus or through her milk. A dog infected with hookworm would experience bloody stool, anaemia, weight loss, pale gums, diarrhoea and low energy level. Skin irritation can be a sign of a severe infestation.

Hookworms can be transmitted to humans by penetration of the skin, making it is possible for people to become infected simply by walking barefoot on infected soil. Hookworms, when transmitted to humans, can cause bleeding in the intestines along with abdominal pain and diarrhoea.   

Tapeworms (Dipylidium caninum)

Tapeworms resemble long, flat ribbons, divided up into segments.  The mature tapeworms head attaches itself to the intestines, segments are filled with eggs, and individual segments break off, to pass via the dog’s faeces into the environment.  Tapeworms, unlike roundworms, need an intermediate host (e.g. flea or mouse – both have different species of tapeworm for different intermediate hosts) that is eaten by the dog.

The most common tapeworm to affect dogs in the UK is the flea tapeworm which uses the flea as an intermediate host in its life cycle.

Swallowing fleas while grooming infects dogs, and once in the gut, the worm larva carried by the flea begins to develop into an adult worm, which can quickly grow to a length of nearly 2 feet.

Adult tapeworms anchor themselves to the gut wall and feed on the dog’s blood. Unsurprisingly, a heavy infestation can cause anaemia (low blood cells), lethargy, loss of appetite and a dull lifeless coat. Unlike roundworms, tapeworms are generally a problem of adult animals.

Tapeworms can also damage human health. The common ones such as the mouse and flea tapeworms are thankfully relatively harmless, but Echinococcus granulosus is a less common tapeworm that can cause serious problems.

Whipworms (Trichuris vulpis)

Whipworms are long, thin (whip-shaped) worms that live in the dog's colon and are not visible to the naked eye. They attach themselves to the intestinal walls and feed off of them which may, in turn, cause intestinal bleeding. Common symptoms of whipworm infestation are anaemia, weight loss, flatulence, diarrhoea with blood or mucus in the stool and lack of energy.

Preventative measures such as immediate removal of faeces from the garden and regular testing of your dog’s faeces to check for infestation are important.

Heartworms (Dirofilaria immitis)

Heartworm, although highly preventable, has the potential to be fatal, if contracted and left untreated.

Heartworm is spread by mosquitoes, mostly during the warm months when mosquitoes are most active. The mosquito becomes infected from biting dogs that carry the disease. These worms destroy the muscle and tissue of the heart, which can cause congestive heart failure and result in death. At this advanced stage, your dog would experience the typical signs of worms such as coughing, lethargy and a dull coat. Unfortunately, there are no symptoms of this disease until it has progressed to an advanced stage. Heartworm is not transmitted in the UK, as we do not have the mosquito vector, therefore treatment and prevention of this worm only becomes important if you are considering travelling abroad.

Lungworms (Angiostrongylus vasorum)

True lungworm - Filaroides osleri, is relatively rare in the UK. It can be a problem in high intensity conditions such as greyhound racing kennels, and can cause bronchial irritation and cough.

Currently there is a lot more focus on Angiostrongylus vasorum, which is also known as French Heartworm. Larvae from this parasite migrate through the gut, lymph nodes, liver, venous system, heart and then lodge in the pulmonary artery. Their eggs then enter the lungs, migrate up the trachea, and are then swallowed. Because of the long migration of the larvae, this parasite causes a variety of problems, from general ill health to excessive bleeding, coughing, or seizures. Severe cases can even lead to death. Because of the variety and vagueness of the symptoms, it can be very difficult to diagnose. The intermediate hosts of Angiostrongylus vasorum are slugs and snails, which dogs may eat accidentally or purposefully.

Prevention of worm infestation

  • Picking up your dog’s faeces when on walks as a standard practice helps prevents soil contamination,

  • Regular visits to the vet and faecal testing is a great way to prevent dog worms, as well as other illnesses. Twice-yearly worm testing is recommended, though most vets in the UK tend to recommend a preventative worming treatment every 3 months in lieu of biannual tests.

  • Make sure your dog is tested for heartworm by your vet before starting a heartworm preventative (this involves blood testing) if you travel abroad with your dog. Dogs travelling to Mediterranean regions of the continent are at increased risk.

  • Flea control is important because fleas are commonly responsible for the spread of tapeworms.

  • Most puppies find faeces quite appetizing. Keep your dog away from faeces: his own as well as others. This is the most common means of worm infestation.

  • Before travelling with your dog to obscure destinations, consult your vet of the potential risks to your dog.

  • Avoid exposing your dog to stray animals, birds and dead rodents, which often harbour immature tapeworms that can mature inside your dog.

  • Try and minimise ingestion of slugs and snails. Regularly clean water bowls and pick up dog toys from the garden and store them securely so slugs and snails cannot creep into the crevices of the toys.

  • Contact your vet if your dog displays any symptoms after receiving worm medication.

Controlling the infestation

Given that worm infestations are so common in the UK, complete prevention over the whole lifetime of your dog is hard to ensure. Control is based on a regular quarterly treatment with a drug that will kill the most common worms (these drugs are called “all-wormers”). These may be given orally as granules, tablets or suspension, and there are spot-ons available that will kill most common worms (only available on prescription from your vet currently).

Not all worm groups are killed by all of the available drugs, so it is important to gain advice as to which products are suitable for your dog’s needs. Tablet wormers will only kill an existing infestation; they do not have residual activity so it is still important to be vigilant for signs of worms in between doses if you are using tablets. Remember to always seek veterinary advice for treatment advice.

  • Granules are tasteless and odourless and can be dissolved into the dogs' food making medication easy.

  • Treats are the same drug in tablet formulation that are given like a treat to the pet.

  • Paste is the same drug in paste formulation so that it can be given directly into the dogs mouth.

  • Suspension is the same drug in a liquid suspension and can be added directly to the food.

  • Tablets often contain a combination of three types of active ingredient, offering complete roundworm and tapeworm coverage for existing infestations.

  • 'Spot-on' preparation, (currently available only through your veterinary surgeon) treats roundworms, fleas and some types of mange, however, It does not treat tapeworm infections.