Hydatid disease (echinococcosis)

Victorian statutory requirement

Notification and school exclusion are not required.

Infectious agent

Echinococcus granulosus (dog tapeworm) is the causative agent.

Identification

Clinical features
Hydatid disease in humans is produced by cysts that are the larval stages of the tapeworm Echinococcus. Brood capsules are formed within cysts,cysts containing 30–40 protoscoleces. Each of these is capable of developing into a single tapeworm. Symptoms depend on the location of the cyst within the body and develop as a result of pressure, leakage or rupture. The most common site for the cysts is the liver. Less commonly brain, lungs and kidneys are affected. The heart, thyroid and bone are uncommonly affected.

Cysts in the body may remain viable or die and calcify. They may be detected on routine X-rays. The prognosis is generally good and depends on the site and potential for rupture and spread. Sudden rupture of the brood capsules and liberation of the daughter cysts may cause fatal anaphylaxis. Persons who have a calcified cyst detected on X-ray may still have active infection.

Method of diagnosis
Diagnosis mayDiagnosis may be made r by plain X-ray, ultrasound or CT scan. If a cyst ruptures, appropriate examination for protoscoleces, brood capsules and cyst wall in sputum, vomitus, faeces orfaeces or urine should be undertaken.

The Casoni skin test has now been replaced by serological tests for hydatid disease. These include fluorescent antibody (FA) and indirect haemagglutination antibody testing.

Incubation period

The incubation period varies from months to years.

Public health significance & occurrence

Hydatid disease occurs worldwide and is mainly associated with sheep farming.

Notification of hydatid infection ceased in Victoria earlyVictoria early in 2001. In the decade prior to 2001 there was an average of 16 notifications per year. Most of these represented infections acquired overseas. Occasional cases of recently acquired hydatid infection have been identified in visitors to rural areas in Victoria where there are infected sheep or dingoes. Urban dogs which accompany travellers are often suspected of being an intermediary of the cycle of transmission to humans. People who trap wild dogs are similarly at risk.

Reservoir

The domestic dog and other canids, definitive hosts for E. granulosus, may harbour thousands of adult tapeworms without being symptomatic.

Felines and most other carnivores are normally not suitable hosts for the parasite.

Intermediate hosts include herbivores, sheep, cattle, goats, pigs, horses, kangaroos, wallabies and camels. Sheep are the major intermediate hosts. Sheep eat the worm eggs from pasture contaminated with dog faeces. These hatch inside the sheep, forming cysts. The life cycle is completed when dogs are infected through eating the offal of infected livestock or wild animals, particularly the liver and lung.

Mode of transmission

Human infection occurs by hand-to-mouth transfer of tapeworm eggs from dog faeces. The larvae penetrate the intestinal mucosa, enter the portal system and are carried to various organs where they produce cysts in which infectious protoscoleces develop.

The important life cycle is dog-sheep-dog. A dingo-wallaby-dingo (or wild dog) sylvatic cycle also occurs. A dog-wild pig-dog cycle has been recognised and poses a special risk for wild pig-hunters.

Period of communicability

Hydatid disease is not transmitted from person to person.

Dogs pass eggs approximately seven weeks after infection. In the absence of reinfection this ends within one year.

Susceptibility & resistance

Young children are more likely to be infected as they are more likely to have closer contact withcontact with infected dogs and they are less likely to have appropriate hygiene habits. There is no evidence to suggest children are more susceptible to infection than adults.

Control measures

Preventive measures
Basic hygiene such as washing hands with soap after gardening or touching the dog and washing vegetables that may have been contaminated by dog faeces, are are important in prevention of this disease.

Control of case
Surgery is often the treatment of choice for infection with Echinococcus granulosus, sometimes combined with prolonged high-doses of the drug albendazole. Percutaneous drainage with ultrasound guidance plus prolonged high-dose albendazole theraphytherapy has been effective for liver cysts. Praziquantel followed by prolonged high-dose albendazole theraphytherapy is used if there is cyst spillage from trauma or surgery. Consult the current version of Therapeutic guidelines: antibiotic (Therapeutic Guidelines Limited). Specialist infectious disease advice should be sought.

Control of contacts
Persons carrying the infection are not contagious to others. Encourage contacts to practice appropriate hygiene and to report early any compatible symptoms.

Control of environment
Dogs kept in and around the case’s house may require veterinary screening for infectionfor hydatid infection.

In general, dogs should be treated with an anti-tapeworm medication such as praziquantel every six weeks in rotation with a broad spectrumbroad-spectrum de-worming preparation to prevent disease in dogs and break the life cycle of the parasite.

Review practices that may have led to infection. In particular, restrict dog access to raw offal from infected sheep or kangaroos to prevent the life cycle continuing. Incinerate or deeply bury infected organs from dead intermediate animal hosts.

Outbreak measures

Not applicable.

Additional sources of information

Victorian Department of Primary Industries
www.dpi.vic.gov.au
Victorian Department of Sustainability and Environment
www.dse.vic.gov.au

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