Dog - Common Canine Worms

Most dog owners are aware that roundworms and tapeworms are common intestinal parasites of the dog.  With the relaxation of quarantine regulations with the introduction of the PETS travel scheme, combined with our warmer summers, some other parasitic worms are now becoming more commonly seen in the UK.

This handout gives a general overview about the problem of endoparasitic worms.  Separate handouts are available on roundworms, tapeworms, heartworms, hookworms, lungworms and whipworms.

What are the different sorts of parasitic worms that infest the dog?

Broadly, the most well known intestinal worms are Toxocara canis, the intestinal roundworm and the tapeworm Dipylidium caninum.  Today, largely due to the development of safe, effective worming preparations, the health risks for our dogs from these two particular worms has diminished considerably.  However, their place is being taken by other worms that until recently were largely unknown in the UK.

Dirofilaria immitis the heartworm, considered an important problem in small animal practice in the United States, are also being seen more frequently in the UK.  Other worms are also being seen more frequently such as Angiostrongylus vasorum, the canine lungworm which does not normally live in the lung at all but in the pulmonary (lung) blood vessels and sometimes the right side of the heart.

With tapeworms (cestodes), Dipylidium caninum was always considered the most common, but other species are also encountered including Echinococcus which is zoonotic (i.e. can infest humans).  This is one of the reasons for the mandatory tapeworm treatment for any dog entering or re-entering the UK under PETS.

It is not all bad news, however.  Whipworms which used to be a problem particularly in kennel dogs, has reduced considerably with the advent of regular, safe, broad spectrum worming programmes.

Roundworms

Toxocara canis, the intestinal roundworm is free living in the bowel. This can infect humans and can cause blindness.  In puppies roundworms can present problems if not controlled with effective worming.  In large numbers they can stunt growth, cause serious digestive upsets and result in considerable gas formation.  This results in a typical pot-bellied appearance.  Roundworms spread directly from dog to dog via infective eggs passed in the faeces, there is no intermediate host.

Tapeworms

Tapeworms require an intermediate host.  Dipylidium caninum is the common tapeworm of the dog in the UK.  It causes few problems in the adult host but in the growing puppy can result in digestive upsets and stunting.  Dipylidium caninum is spread by the flea as intermediate host and effective treatment must also cover environmental flea control, that is the dog catches the worm from the flea, not directly from other dogs.

Echinococcus spp., another type of tapeworm, is important because of its zoonotic potential as humans can be infected.  Sheep and sometimes man can act as the intermediate host in which the immature forms of Echinococcus develop inside cysts which grow in various organs.  In man the usual organs affected are the lungs and the brain.

Control measures involving regular de-worming of the dog together with an avoidance of feeding raw or under-cooked offal are obvious precautions.

Tapeworms found in adult dogs usually cause few problems, however occasionally puppies are infested and depending on the type of worm involved, their sheer volume can cause serious blockages to the bowel.

Heartworms

Heartworm disease is caused by Dirofilaria immitis a large worm, measuring up to 16 cm (5½ inches).  This worm is a major problem in parts of Southern Europe and in the United States.  The condition is being increasingly diagnosed in the UK, probably as a result of the relaxation of quarantine restrictions which now allow British dogs to travel to areas where heartworm is a problem and return to the UK without having to undergo quarantine.

Heartworm disease is one of the most important canine conditions seen in some parts of the US.  The development to the adult stage takes about six months after infection following a bite by a mosquito carrying the infective larvae, Microfilariae.  Typical signs are fatigue on exercise, coughing and poor condition.

Hookworms

Hookworms, particularly Ancylostoma spp are one of the most pathogenic (disease causing) parasites of the dog.  Although not a major problem in British dogs at present, this tropical hookworm, approximate size 1-2 cm (½ to 1 inch) attaches itself to the lining of the bowel and as a result of blood sucking activities can cause severe anaemia.  Infective larvae enter the host either through the mouth or through the skin (particularly of the feet).  Eczema and secondary bacterial infection can result due to the irritation as they burrow through the skin.

Following increased foreign travel by British dogs under the Pet Passport Scheme hookworm disease is now being diagnosed regularly in the UK.

Lungworms

Angiostrongylus vasorum the canine lungworm lives usually in the pulmonary (lung) blood vessels or sometimes the heart of the dog rather than in the lung tissue itself.  Affected dogs are often asymptomatic, show no signs at all, or merely minor exercise intolerance, lethargy and coughing.  Since the worm usually affects younger dogs these signs may be noticed.

Canine lungworm has been known to exist in southern England and Wales for many years but cases are now occurring in all parts of the UK.  This may in part be due to milder weather since to complete the life cycle Angiostrongylus depends upon molluscs, slugs or snails, which as a result of mild winters maybe much more common in the UK.  Please see a separate handout on Lungworms and consult us if you have any concerns.  Remember that not all multi- worming preparations are effective against lungworm.  We will be happy to supply an appropriate preparation if required.

Whipworms

Whipworms, Trichuris vulpis, are approximately 7 cm (3 inches) long and live in the large intestine (caecum and colon) of dogs.  The eggs, passed in the dog's faeces, are very resistant and can last for years on the surface of the ground.  Today, due to effective endoparasiticides whipworms are relatively uncommon.

Treatment against worms

Today many effective drugs are available to control worms in the dog.  Many of these are available over-the-counter without prescription.  However, effective worm control involves the choice of an appropriate preparation which has to be regularly repeated.  Please contact us and we will be happy to advise and supply suitable preparations together with appropriate dosing instructions.