Part of the Communicable Disease Control Manual
Chapter reviewed and updated in December 2017. A description of changes can be found at Updates to the Communicable Disease Control Manual.
- Epidemiology in New Zealand
- Case definition
- Spread of infection
- Notification procedure
- Management of case
- Management of contacts
- Other control measures
The larval (cystic or hydatid) stage of the dog tapeworm Echinococcus granulosus causes hydatid disease in humans and cattle. The Ministry of Agriculture and Forestry declared New Zealand provisionally free of hydatids in 2002.
More detailed epidemiological information is available on the Institute of Environmental Science and Research (ESR) surveillance website.
Cysts usually develop in the liver or lung (occasionally the spleen, brain, heart, kidney or bones) and slowly grow to 5–10 cm in length. They may persist for years or decades without symptoms and often are detected incidentally. Local pressure effects in a confined space may lead to symptoms. Rarely, cysts rupture into the biliary tree or a bronchus causing obstruction, secondary bacterial infection, an allergic reaction or secondary spread.
Even asymptomatic cysts should be notified.
Radiologically, hydatid cysts are single or multiple and may have a rim of calcification. There may be peripheral blood eosinophilia.
Laboratory test for diagnosis
Laboratory definitive evidence for a confirmed case requires at least one of the following:
- identification of E. granulosus in cyst fluid or, rarely, sputum
- positive serological tests for E. granulosus (eg hydatid haemagglutination or complement fixation test) in the context of radiological or other organ imaging evidence of characteristic cystic disease.
- Under investigation: A case that has been notified, but information is not yet available to classify it as probable or confirmed.
- Probable: Not applicable
- Confirmed: Histopathological or other demonstration of E. granulosus cysts or radiological or other organ imaging evidence of characteristic cystic disease with a positive serological test.
- Not a case: A case that has been investigated and subsequently found not to meet the case definition.
Definitive hosts are dogs and other canids; intermediate hosts include sheep, cattle, goats, pigs and horses.
Years to decades, depending on number and location of cysts and how rapidly they grow.
Mode of transmission
In New Zealand, the definitive host has been the dog. E. granulosus adult tapeworms inhabit the dog’s intestines, and eggs are excreted into the environment. Sheep, cattle, goats, pigs, horses and humans accidentally ingest these eggs, which hatch in the intestine, and the resultant onchospheres penetrate the mucosa, migrate to tissues and multiply within cysts. Hydatids is not directly transmitted from person to person.
Period of communicability
Dogs begin to pass eggs 5–7 weeks after infection. Most infections resolve in 6 months, although occasionally adult worms survive 2–3 years. Eggs are particularly resistant to environmental conditions and may survive months in paddocks or gardens.
Attending medical practitioners or laboratories must immediately notify the local medical officer of health of suspected cases. Notification should not await confirmation.
Obtain a history of travel and dog contact, especially farm dogs. Ensure serological diagnosis has been attempted.
Advise the case and their caregivers of the nature of the disease and its mode of transmission.
Identification of source
In instances where recent infection is suspected (within 2 years), liaise with the Ministry for Primary Industries to investigate potential dog infection in the region. See ‘Reporting’ below.
The slaughtering of cows, sheep, deer, goats and pigs must be carried out in an approved killing facility within a dog-proof enclosure to prevent dogs from having access to uncooked viscera. The offal from these animals must not be fed to dogs unless it is first cooked by boiling for a minimum of 30 minutes.
Follow local territorial authority or regional council regulations on dog worm treatment.
Imported livestock should be tested and tracked.
Encourage hand washing after contact with dogs or dog faeces, especially before eating. Young children are especially at risk.
Ensure complete case information is entered into EpiSurv. All species of Echinococcus are notifiable organisms in New Zealand under the Biosecurity Act 1993.
On receiving a notification, medical officers of health should immediately notify the Director of Public Health at the Ministry of Health.
The Ministry of Health will inform the appropriate staff in the Ministry for Primary Industries so that further investigation of the source can be undertaken.