Toxocara canis

Toxocara canis are about 7 -10 cm long and the most common roundworm of the dog. They live in the dog’s intestine where they consume partly digested food.

The dog can become infested when it accidently eats the microscopic eggs. These hatch in the intestine and the larvae burrow through the wall of the intestine and travel in the blood and body tissues to the lung where they are coughed up and swallowed and eventually develop into adult worms in the gut. These adults lay eggs which pass out in the stools and the life cycle is completed.

In the bitch, some of the migrating larvae form cysts in the muscles. These are stimulated to continue their development in the latter stages of pregnancy and can pass to the puppies across the placenta and in the colostrum. Thus almost all puppies are born with worms.

Toxocara worms are not particularly harmful to adult dogs, though in large numbers can cause vomiting, diarrhea, weight loss and a pot-bellied appearance in puppies. Occasionally adult worms can be seen in the vomit or faeces, but generally diagnosis is confirmed by finding eggs in the faeces by microscopic examination.

Can Toxocara canis affect humans?

Yes; if a person (usually a young child) accidently ingests the eggs, there is a risk that they may hatch in the intestine and the larvae may penetrate the wall of the gut and migrate through the body. Find out more.
How are roundworms controlled? Find out more.


Whipworms, Trichuris vulpis, are about 7 cm long and are roundworms that live in the large intestine of dogs where they cause severe irritation to the lining of these organs.  This results in watery, bloody diarrhoea, weight loss, and general debilitation. Microscopic eggs are passed in the faeces. These are swallowed and return to the lower intestinal tract to complete the life cycle.

Infestation is more common in kennels, particularly those with grass runs. Diagnosis is confirmed by identification of eggs in the faeces by microscopy. Whipworms do not affect humans.


Hookworms are roundworms about 3mm in length that attach to the wall of the intestine by hooked mouthparts. Dogs can become infected by larvae penetrating the skin (often between the toes), followed by migration to the gut. In addition larvae can pass from bitches to puppies via the placenta and the colostrum.

Adult worms suck blood from vessels in the intestine and if in large numbers can cause anaemia, bloody diarrhea and weight loss. Skin irritation and itching can be one of the common signs of a heavily infested environment. Kennels can sometimes have a problem with hookworms.

Diagnosis is confirmed by identifying eggs in the faeces by microscopy. Adult hookworms do not infect humans; however, the larvae can burrow into human skin where it causes irritation, though the worms do not mature into adults.  Direct contact of human skin with moist, hookworm infested soil is required.  Fortunately, this does not occur very often if normal hygiene practices are observed.


Heartworm disease is a serious and potentially fatal disease in dogs caused by a worm called Dirofilaria immitis. Transmission by mosquitoes is essential and so the disease is restricted to geographic areas where these are present.

This is an important consideration if you are intending to take your dog on holiday to these areas. Find out more.


The adult worm Angiostrongylus vasorum lives in the main arteries of the lungs in dogs and foxes. The females lay eggs which are carried in the blood and lodge in the tiny capillaries of the lung where they hatch into larvae. These are coughed up, swallowed and pass out in the faeces. They are then ingested by slugs and snails where they develop further. Eventually these infected snails and slugs are eaten by dogs or foxes and the life cycle is completed. Direct transmission from dog or fox to dog is not possible.

The disease can be very serious and death can result. Signs include a persistent cough and breathing difficulties. However, there may also be poor blood clotting with hemorrhages, seizures, abdominal pain and lethargy. Your veterinarian can confirm the diagnosis by identifying the larvae in the faeces.

Not all worming products will kill lungworm, and some of the effective treatments may be relatively toxic in some dog breeds. So it is important to consult your veterinarian for the best advice. Attempting to control slugs and snails using slug bait is potentially dangerous as these products are toxic to dogs.



The most common tapeworm of dogs is Dipylidium caninum.  This parasite attaches to the small intestinal wall by hook-like mouthparts.  Adult tapeworms may reach 20 cm. in length, made up of many individual segments. The terminal segments break off and are passed in the faeces.

They look like grains of rice and contain eggs which are released when the segment dries.  Mobile segments may sometimes be seen crawling near the dog’s anus, or dried segments may be stuck to the hair. For the life cycle to continue, the tapeworm egg must be swallowed by a flea larva. The dog becomes infected when it subsequently swallows a flea and the new adult worm is released to attach to the wall of the intestine.

Dipylidium is generally not that harmful though can cause weight loss, vomiting and diarrhea if in large numbers. The dog may drag its anus across the ground or carpet because the segments are irritating to the skin in this area. This parasite does not generally affect humans, and should not be confused with pinworm infections in children. There are very rare reports of children being infected following ingestion of fleas.

Diagnosis is usually made by recognizing the characteristic grain of rice like segments. There are a number of effective medications available for treatment, and clearly flea control is an important part of the control programme.

Echinococcus and Hydatid disease

Another group of tapeworms is called Echinococcus and this is of particular concern as a threat to human health. The adult tapeworms live in the gut of dogs and other carnivores and the eggs are passed out in the faeces. These eggs are ingested by an intermediate host where they form hydatid cysts within the body.

The intermediate hosts of Echinococcus granulosus include sheep, goats and wild herbivores. A dog becomes infected when it eats a sheep carcass containing hydatid cysts. Worm heads within the in the hydatid cyst grow into a small tapeworm in the gut of the dog and produce eggs. The intermediate hosts of Echinococcus multilocularis are generally small rodents. Find out more.


The brief summary above indicates this is very important, but that there are a number of considerations and different programmes may be more suitable in varying situations.

There are now many effective products on the market, some of which are given by tablet, some as “spot-on” and some by injection. Not all products kill the full range of worms; some might have the advantage that they also control other parasites such as fleas, ticks or mites.

Important questions:

  • Where do you live?
  • Where will you visit for holidays?
  •  Do you have a breeding bitch and puppies in the home?
  •  Do you have young children?

The answers to all these questions will have an impact on the best choice of programme for your particular situation. Your veterinarian is best placed to advise you.

Fortunately there are effective medications available and these together with hygienic precautions will help to make the real hazards posed a very low risk to your dog and your family.



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