Hydatid disease (echinococcosis)

Notification requirement for hydatid disease (echinococcosis)

Notification is not required.

Primary school and children’s services centre exclusion for hydatid disease (echinococcosis)

Exclusion is not required.

Infectious agent of hydatid disease (echinococcosis)

Echinococcus granulosus (dog tapeworm) is the causative agent.

Identification of hydatid disease (echinococcosis)

Clinical features

Hydatid disease in humans is produced by cysts that are the larval stages of the dog tapeworm, E. granulosus. Brood capsules are formed within 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 (which may be detected on X-ray). The prognosis is generally good, and depends on the site and the potential for rupture and spread. Sudden rupture of the brood capsules, liberation of the daughter cysts and exposure of parasite antigens may cause fatal anaphylaxis. People who have a calcified cyst detected on X-ray may still have active infection.

Diagnosis

Diagnosis may be suggested by imaging (plain X-ray, ultrasound or computed tomography – CT – scan). If a cyst ruptures, appropriate examination for protoscoleces, brood capsules and cyst wall in sputum, vomitus, faeces or urine should be undertaken.

Diagnosis is confirmed by serological tests for hydatid disease. These include fluorescent antibody and indirect haemagglutination antibody testing. Serology is 80–100 per cent sensitive and 88–96 per cent specific for liver disease (less for lung or other organ involvement). Eosinophilia is not a consistent finding.

Incubation period of Echinococcus granulosus

The incubation period varies from months to years.

Public health significance and occurrence of hydatid disease (echinococcosis)

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

Notification of hydatid infection ceased in Victoria early in 2001. In the decade before 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 that accompany travellers are often suspected of being an intermediary in the cycle of transmission to humans. People who trap wild dogs are similarly at risk.

Reservoir of Echinococcus granulosus

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 of Echinococcus granulosus

Human infection occurs by hand-to-mouth transfer of viable tapeworm eggs from dog faeces. The parasite eggs, which can remain viable for weeks, are distributed via local environmental contamination by faeces of tapeworm-infected canines. 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 of hydatid disease (echinococcosis)

Hydatid disease is not transmitted from person to person.

Dogs pass eggs in faeces approximately 7 weeks after infection. In the absence of reinfection, this ends within 1 year.

Susceptibility and resistance to hydatid disease (echinococcosis)

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

Control measures for hydatid disease (echinococcosis)

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 important in prevention of this disease.

Control of case

Surgery is often the treatment of choice for infection with E. granulosus, sometimes combined with prolonged high doses of albendazole. Percutaneous drainage with ultrasound guidance plus prolonged high-dose albendazole therapy has also been effective for liver cysts. Praziquantel followed by prolonged high-dose albendazole therapy is used if there is cyst spillage from trauma or surgery. A combination of these agents can be used in the peri-operative setting to reduce the risk of spread. For inoperable cysts, a PAIR procedure (puncture, aspiration, injection, re-aspiration) under CT guidance with concurrent anthelmintic therapy can be performed. Consult the current version of Therapeutic guidelines: antibiotic. Specialist infectious diseases advice should be sought.

Control of contacts

People carrying the infection are not contagious to others. Encourage contacts to practise 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 hydatid infection.

In general, dogs should be treated with an anti-tapeworm medication such as praziquantel every 6 weeks, in rotation with a broad-spectrum deworming 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 for hydatid disease (echinococcosis)

Not applicable.