Hydatid Disease

Human echinococcosis is a zoonotic disease that is caused by a parasite, namely tapeworms of the genus Echinococcus. Echinococcosis occurs in two forms that are of public health relevance in humans: cystic echinococcosis (CE), also known as hydatid disease or hydatidosis, caused by Echinococcus granulosus, and alveolar echinococcosis (AE), caused by infection with E. multilocularis. Only hydatid disease is notifiable in NZ.

CE is globally distributed and found in every continent except Antarctica. The larval (cystic or hydatid) stage of the dog tapeworm Echinococcus granulosus causes hydatid disease in sheep, cattle, goats, pigs and horses which are the intermediate hosts. 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.

AE is confined to the northern hemisphere, in particular to regions of China, the Russian Federation and countries in continental Europe and North America and it is not found in New Zealand. It is not notifiable in New Zealand however imported human cases may occur.

In CE, hydatid 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. Symptoms depend on the location of the cysts and the pressure exerted on the surrounding tissues. Abdominal pain, nausea and vomiting are commonly seen when hydatids occur in the liver. If the lungs are affected, clinical signs include chronic cough, chest pain and shortness of breath. Non-specific signs include anorexia, weight loss and weakness. Rarely, cysts rupture and cause an allergic reaction (possibly life-threatening) and cyst dissemination.

Radiologically, hydatid cysts are single or multiple and may have a rim of calcification. There may be peripheral blood eosinophilia.

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.

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 accidently ingest these eggs, which hatch in the intestine, and the resultant onchospheres penetrate the mucosa, migrate to tissues and multiply within cysts. Humans are aberrant intermediate hosts and CE is not directly transmitted from person to person.

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.

See Appendix 5: Escalation pathways for more information

Obtain a history of travel and dog contact, especially farm dogs. Ensure serological diagnosis has been attempted where there is any doubt that infection may have occurred since 2002, if it hasn’t previously been done.

Nil.

Advise the case and their caregivers of the nature of the disease and its mode of transmission.

Not applicable.

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.

Nil.

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 notify the Director of Public Health at the Ministry of Health if infection is suspected to be acquired in New Zealand after 2002[1].

The Ministry of Health will then inform the appropriate staff in the Ministry for Primary Industries, so that further investigation of the source can be undertaken.

[1] The Ministry for Primary Industries declared New Zealand provisionally free of hydatids in 2002.