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Hydatid disease - including symptoms, treatment and prevention

Hydatid disease is caused by infection with a small tapeworm parasite called Echinococcus granulosus.

How hydatid is spread

In Australia, most infections are passed between sheep and dogs, although other animals including goats, horses, kangaroos, dingoes and foxes may be involved.

The hydatid parasite is carried by dogs in their bowel, without any symptoms of infection. Sheep become infected while grazing in areas contaminated with dog faeces. Dogs become infected by eating the uncooked organs of infected sheep.

People become infected by ingesting (eating) eggs of the parasite, usually when there is hand-to-mouth transfer of eggs in dog faeces. This can occur when handling dogs or objects (including food and water) soiled with dog faeces. Person-to-person or sheep-to-person transmission does not occur.

Signs and symptoms

The parasites form slowly enlarging fluid-filled cysts which may become very large. Cysts occur most commonly in the liver or lungs, but may occur in any organ, including the heart, brain and bones. Cysts often do not cause symptoms unless they become very large or break.

Diagnosis

Hydatid cysts are diagnosed by x-ray, ultrasound, CT or MRI scans and may sometimes be confirmed by a blood test. Occasionally, microscopic examination of the cyst fluid is required.

Incubation period

(time between becoming infected and developing symptoms)

Variable, from months to years, depending upon the number and location of cysts and how rapidly they grow.

Infectious period

(time during which an infected person can infect others)

There is no direct person-to-person transmission. Dogs begin to pass parasite eggs about 7 weeks after infection. Most infections in dogs disappear without treatment within 6 months, but dogs may be infected repeatedly.

Treatment

Surgical removal of the cysts is the most common treatment, often in combination with specific anti-parasitic drug therapy.

Prevention

  • Exclusion from childcare, preschool, school or work is not necessary
  • thorough hand washing after contact with dogs, or objects that may be contaminated with dog faeces (for example, garden soil)
  • do not let dogs lick your face
  • regular worming of pet and working dogs with a treatment that covers hydatid tapeworm (check the label to make sure it contains praziquantel, or ask your vet)
  • dogs must not be fed raw offal.

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