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Nature of the disease
Hydatid disease (echinococcosis) is a parasitic infection caused by tapeworms Echinococcus spp., 4 species have been associated with echiniococcosis. The disease in intermediate hosts is caused by hydatid cysts growing in the body. Hydatidosis is a severe zoonosis. 
OIE List B disease
Susceptible species
The definitive hosts are dogs, wild dogs and foxes. Sheep, pigs, goats and some macropods can be intermediate hosts. 

Humans and cattle can be infected, but do not cause infection in the definitive host.

For Echinococcus granulosusn, the dog–sheep cycle is the most important cycle of infection.

For Echinococcus multilocularis, the fox-rodent cycle is the most important.

For Echinococcus oligarthrus, the wild felids-large rodent cycle is the most important.

For Echinococcus vogeli, the bush dogs-large rodent cycle is the most important.

E. granulosus is widely distributed and is found in most of the important sheep and goat rearing regions of the world. It occurs in Africa, North and South America, Europe, the Middle East and Asia. In the Pacific, hydatids occurs in Australia and New Zealand where it has not been recorded since 2000.

E. multilocularis seems to be only found in cold countries; E. oligarthrus and E. vogeli are only found in Central and South America.

Clinical signs (E. granulosus)
Most dogs with hydatids show no signs of infection. If a large number of tapeworms are present in a dog, diarrhoea may be seen, but this is uncommon. 

Clinical signs are also not obvious in sheep and the disease is rarely diagnosed before slaughter. Sometimes, depending on the localisation of the cysts, the following signs can be seen:

  • Bronchopneumonia,
  • Hepatic disorders leading to ascites and jaundice,
  • Heart failure,
  • Slow growing, weakness and lameness.

In humans, hydatid cysts can establish in the brain, kidneys, bone, liver and other tissues. The disease is caused by hydatid cysts growing in the body. Clinical signs can take months to years to develop and become more apparent as the cysts grow. As the cysts increase in size they can cause the body to become distended. When the cysts grow in vital organs, they may disrupt the function and lead to signs of disorders related to disruption of the organ functions. The most serious development is when the cyst ruptures and causes an anaphylactic reaction, which may be fatal.

Post-mortem findings (E. granulosus)
There is little to be seen in dogs, since the adult tapeworms attached to the dog’s small intestine are only 6 mm long.

In intermediate hosts, the characteristic lesions are fluid filled cysts. These grow slowly but may eventually reach the size of a football or larger. Most cysts are found in the lungs and the liver. Other sites are the brain, kidneys, heart, omentum, spleen and bone.

In Equids cysts are almost exclusively found in the liver.

Differential diagnosis (E. granulosus)
Other tapeworms with ruminant intermediate hosts include:
  • Taenia ovis 
  • Taenia saginata 
  • Taenia hydatigena 
Specimens required for diagnosis (E. granulosus)
In dogs, diagnosis is based on microscopic identification of E. granulosus eggs in a sample of duodenal mucus shed in the faeces. However, E. granulosus cannot be differentiated from other Echinococcus spp. and Taenia spp. eggs.

Samples of intestinal contents can be obtained by purgation with arecoline (1-2 mg/kg) and microscopic observation permits to observe adult worms.

In intermediate or accidental hosts serological tests can be performed out from blood using ELISA, IFI, IDR or immuno-electrophoresis. ELISA tests also exist for dogs.

Transmission   (E. granulosus)
Dogs are commonly infected by ingesting cysts containing protoscolices (by eating contaminated offal). Cysts can be either fertile or sterile. The proportion of sterile cysts varies with the host — 90% or more of cysts in cattle, 20% of cysts in pigs and 8% of cysts in sheep are sterile. If cysts burst in the intermediate host, new cysts are formed by the protoscolices.

After ingestion by dogs, the protoscolices attach to the small intestine and develop into adult tapeworms. At about seven weeks after infection, dogs start shedding gravid tapeworm sections. These sections release eggs as they travel down the gut. The eggs then contaminate the faeces and are spread in the environment.
Intermediate hosts such as sheep become infected by ingesting eggs. The embryo penetrates the intestinal wall and is carried in the blood to the liver by portal circulation. About 20% are then carried to the lungs and another 20% to other areas of the body such as the brain, kidneys, heart, omentum, spleen and bone.

Humans usually become infected by ingesting eggs that have contaminated the general environment. Eggs may be present on vegetables and fruit contaminated by dog faeces. Humans can be directly contaminated by petting dogs or being lick by dogs. Humans are not infected by eating meat containing hydatid cysts.

Risk of introduction   (E. granulosus)
Hydatid tapeworms are most likely to be introduced to a previously free country through the importation of infected dogs. These are capable of producing large number of eggs that could contaminate the environment and set up an infection cycle if ruminants are exposed. Dogs coming from an infected country should be treated with praziquantel.
Importation of sheep could also pose a risk. If these come from endemic areas, they could be harbouring hydatid cysts. If dogs get access to infected offal, an infection cycle could become established.
Control / vaccines  (E. granulosus)
There is no treatment for sheep with hydatid cysts.

In humans, surgical removal of cysts is the treatment of choice.

Dogs can be treated with anthelmintics. Praziquantel (‘Droncit’) is highly effective in removing the tapeworms, but provides no protection against reinfection. 

The activities of dogs should be controlled to help prevent transmission of the parasite. Measures to stop the dog–sheep cycle include:

  • Preventing dogs from eating infected offal,
  • Preventing infected dogs from defecating on pastures grazed by sheep.

For human protection, dogs should be kept out of vegetable plots to prevent contamination of the vegetables by eggs from the dog’s faeces. Hygienic measures should also be observed (prevent dog licking hands, hand washing before heating).

  • BUSSIERAS J, CHERMETTE R, Helminthologie In Parasitologie Vétérinaire, Ecole Nationale Vétérinaire D'Alfort, 1992, p 49-53; 111-116
  • Office International des Epizooties, 2002
  • SOULSBY EJL, Helminths, Echinococcus In Helminths, Arthropods and Protozoa of Domesticated Animals, Lea and Febiger Inc, 7th ed, 1982, Philadelphia, p 119-125
  • Tapeworms, In Merck Veterinary Manual, National Publishing Inc. Eight ed, 1998, Philadelphia, p 320-321