Echinococcus tapeworms in dogs – infection and echinococcosis

Overview

Echinococcus canadensis occurs in parts of northern Europe. Its natural cycle involves wolves and deer-family animals. Dogs can also acquire this infection.

Echinococcus multilocularis is a different species that has not been detected in animals in some countries. Some countries hold official infection-free status for this parasite. However, E. multilocularis occurs in Sweden and Estonia, for example.

Carrying adult worms in the intestine and disease caused by larval cysts growing in tissues are different situations. The severe tissue form in dogs, alveolar echinococcosis, is rare. Infection is treated even in a dog without symptoms because of the risk to people.

E. canadensis has been found in particular areas of northern Europe. Since 2017, northern European records have also identified it in moose and wolves west of its previously recognised local range. One northern European surveillance programme examines 300–500 foxes and raccoon dogs annually for E. multilocularis.

Causes

Prey and its internal organs transmit intestinal infection

A definitive host is an animal in whose intestine the tapeworm becomes an adult. Larval cysts instead develop in an intermediate host's body. A dog acquires intestinal infection by eating prey containing cysts or its raw internal organs.

Rodents are important intermediate hosts for E. multilocularis, and dogs may catch them outdoors. For E. canadensis, a possible source is an organ containing parasitic cysts from a moose or reindeer, for example. Adult E. multilocularis is only around 1.2–4.5 millimetres long.

Adult E. granulosus tapeworms are around 2–7 millimetres long. The interval from Echinococcus infection to egg shedding may be 1–2 months. Maturity and egg shedding can begin as early as 4–5 weeks.

Swallowing eggs can cause the rare tissue form

Eggs are infective immediately after passing into the environment with faeces. If a dog swallows E. multilocularis eggs, it may develop the tissue form rather than the usual intestinal infection. Larvae can then grow into multilocular cystic lesions in the liver.

The sticky egg surface helps eggs adhere to animal coats and objects, for example.

Risk factors

A free-roaming hunting dog may be exposed by eating an infected rodent in an area where E. multilocularis occurs. A hunting dog's access to raw game offal increases possible exposure. Travel destination and the dog's scavenging habits also affect risk.

Intestinal infections are found more often in young dogs than older ones. The mean age of dogs with the tissue form in Europe and Canada has been around 3–4 years. It has been identified in a dog as young as 1 year. No clear breed predisposition has been demonstrated.

Older dogs can also acquire another infection because there is no evidence of protective immunity. Drinking water contaminated with eggs or eating wild canid faeces may expose a dog to the tissue form.

Typical symptoms

Ordinary intestinal carriage of adult worms usually causes no signs, even with a heavy burden. The small segments almost always go unnoticed by the naked eye.

The following signs relate to the rare tissue form, in which larvae grow particularly in the liver.

• Abdominal girth gradually increases, sometimes despite otherwise relatively good health.

• Appetite declines and your dog leaves meals uneaten.

• Your dog may vomit and seem nauseous.

• Your dog loses weight and has less stamina.

• Breathing may become difficult.

• Intermittent diarrhoea may occur.

Fever is a possible but uncommon sign of the tissue form. Bloody diarrhoea has occasionally also been described with adult worms living in the intestine.

Complications and consequences

Liver damage relates to the tissue form

Alveolar cysts can invade surrounding tissues like a malignant tumour. Lesions can spread from the liver to the lungs or brain, for example. Severe liver damage can cause fluid accumulation in the abdomen, called ascites.

The tissue form causing haemorrhagic liver lesions and organ failure has a poor outlook. Early detection and effective treatment influence survival prospects.

A symptom-free carrier can infect people

People can become infected by swallowing eggs originating from a dog's faeces or coat. In a person's body, larvae can form cysts particularly in the liver and lungs. Human tissue disease caused by E. multilocularis can be life-threatening.

Simply touching a dog's tissue cyst is not the usual human transmission route: infection comes from eggs. However, a dog with the tissue form may also have an intestinal infection shedding eggs.

Diagnosis at the vet

Faecal testing often requires species confirmation

The investigating vet first assesses travel history and access to rodents, game and raw offal. Routine faecal microscopy can miss infection. Sensitivity for detecting E. multilocularis eggs with centrifugal flotation has been described as only around 30%.

Under the microscope, the eggs resemble those of other Taenia-group tapeworms. Finding tapeworm eggs alone therefore does not confirm the Echinococcus species. Faecal PCR looks for parasite genetic material and can distinguish different Echinococcus species.

Handling a suspected Echinococcus sample requires particular care because the eggs are infective. PCR is performed by diagnostic laboratories offering the method.

Eggs are shed intermittently, making infection harder to detect from a single faecal sample.

Liver lesions are investigated separately

Tissue-form cysts may resemble liver tumours on ultrasound or radiographs. PCR of tissue or cyst fluid can be used for confirmation. Parasite structures may also be visible in the sample.

Fine-needle sampling is planned carefully because parasite material escaping from a cyst can spread lesions within the abdomen. Cyst leakage can also cause a severe allergic reaction, called anaphylaxis. With the tissue form, faeces are also tested for possible concurrent intestinal carriage.

Histology, microscopic assessment of tissue structure, can help identify a parasitic cyst. A cyst sample does not always contain recognisable developing worm structures even when the lesion is parasitic. Antibody tests are not routinely used in domestic animals. Cross-reactions with other Taenia tapeworms may complicate interpretation.

Treatment

Intestinal infection is treated with a veterinary-selected medicine

Praziquantel is effective against adult intestinal worms, and the vet decides on its use. Treatment aims to stop environmental contamination with eggs and protect people and other animals. It also involves preventing hunting and the eating of raw, high-risk offal.

Medication does not protect against reinfection if the dog later eats another infection source. Eggs may still be shed for 3 days after treatment. During this time, activity is restricted according to veterinary instructions and faeces are collected particularly carefully.

The dog's coat is shampooed to remove adherent worm eggs. Those caring for an infected animal use gloves and protective clothing appropriate to the situation.

The tissue form needs long-term specialist care

Praziquantel does not treat E. multilocularis larvae growing in tissues. Medication for the tissue form may include albendazole under close veterinary monitoring. Medical care may continue for a prolonged period.

Advanced disease may require lifelong treatment. Albendazole can suppress bone marrow function, so blood cell counts are monitored. A cystic lesion that can be completely removed may be treated surgically alongside medication.

With inoperable disease, prolonged medication may suppress cyst growth or extend survival. Effectiveness also depends on how far the disease has progressed.

Prevention

Do not allow your dog to catch rodents or eat carcasses and raw game offal. A lead or secure fenced exercise area reduces access to prey. Remove a suspected infected dog's faeces promptly from the environment.

Wash hands thoroughly after handling faeces and before eating. Eggs may also reach the mouth through unwashed vegetables or contaminated surface water. Eggs withstand ordinary freezing even at −20°C, so a home freezer is not considered a reliable decontamination method.

Some destinations require veterinary-administered treatment against E. multilocularis for incoming dogs. Exemptions apply to some direct travel routes. Where required, treatment and its timing are recorded in the pet passport.

Dispose of moose and reindeer offal, particularly lungs, so that dogs and wildlife cannot access it. Cook moose or reindeer internal organs thoroughly before giving them to a dog. Wear gloves and wash hands when handling hunted wolves, foxes or raccoon dogs.

Some national guidance does not restrict picking or using wild berries because of Echinococcus. Keep canids away from growing areas and prevent their faeces contaminating surface water. Use good-quality water for irrigation and washing produce.

E. multilocularis eggs have survived for 2–8 months in the environment under German climatic conditions. Under some conditions, eggs can remain infective for 2 years or longer. Wear protective gloves when handling soil and rinse edible vegetables before use.

Important for dog owners

Before the appointment, record travel countries and dates and whether your dog has eaten rodents or game offal. Bring the pet passport and previous parasite test results. Mention the suspicion when booking so faecal sample collection and delivery can be planned safely.

The infection risk from handling eggs also affects veterinary and laboratory staff. If infection is confirmed, you should also discuss possible personal exposure with a healthcare professional.

Travel-related parasite treatment does not replace other entry requirements. Medication given before departure alone does not prevent your dog acquiring infection later abroad.

Check current treatment and documentation requirements for your route with the relevant national veterinary authority before departure. Agree with your vet how the plan changes if the route or return date changes.

Some countries require owners to report suspected E. multilocularis infection in a canid promptly to an official vet. Official veterinary services may then notify the relevant public-health doctor of confirmed infection.

Frequently asked questions

Can a dog that looks completely healthy carry Echinococcus?

Yes: intestinal carriage of adult tapeworms usually causes no visible signs. The dog can still shed eggs in faeces that are infective to people. Veterinary risk assessment therefore also considers hunting habits and access to raw offal.

Do different Echinococcus species have the same distribution?

Echinococcus canadensis occurs in parts of northern Europe. E. multilocularis has not been detected in animals in some countries. Some countries hold official freedom from this parasite. Distinguishing these species matters when assessing hunting-dog risks and travel requirements.

Can Echinococcus be seen in a dog's faeces?

Usually not, because adult worms and their segments are very small. Even routine microscopy cannot distinguish Echinococcus eggs from Taenia tapeworm eggs. Faecal PCR can confirm the species by looking for parasite genetic material rather than relying on appearance.

Does worming medication prevent a new Echinococcus infection?

No, if the dog can eat another source after medication. Intestinal treatment is therefore combined with preventing hunting and eating high-risk offal. Praziquantel also does not treat larvae growing in the dog's tissues: its effect targets intestinal worms.

Can a parasitic liver cyst in a dog infect people?

People become infected by swallowing infective eggs, rather than simply touching a dog's tissue cysts. However, a dog with the tissue form may simultaneously have an egg-shedding intestinal infection. Faeces are therefore also tested for concurrent intestinal infection even when the main finding is in the liver.