What is Hydatid Disease?
Hydatid disease is caused by a tiny tapeworm called Echinococcus granulosus. The parasite normally cycles between dogs and livestock such as sheep, cattle, goats and pigs. Dogs become infected by eating animal organs containing hydatid cysts, allowing adult tapeworms to develop in their intestines and release eggs in their faeces. These eggs are immediately infectious and can contaminate soil, food, water and hands. Livestock become infected by swallowing the eggs, after which larvae migrate through the body and slowly develop into fluid-filled cysts, particularly in the liver and lungs. Humans are accidental hosts who become infected by similarly swallowing the eggs, often through contaminated hands, food or water.
Hydatid cysts can enlarge slowly over many years, often without causing symptoms, before eventually affecting the liver, lungs or other organs. The parasite is particularly associated with sheep and livestock-raising regions of the Mediterranean, Middle East, Central Asia, Australia, New Zealand, South Africa and South America. For travellers, exposure is most relevant when visiting pastoral or farming communities where dogs have access to livestock remains. Avoiding contact with unfamiliar dogs, particularly working or farm dogs, and practising careful hand hygiene after contact with animals or soil can reduce the risk.
The World Health Organization estimates more than 1 million people are affected with echinococcosis.
FAQs
How can I catch hydatid disease? Do I need to be near sheep?
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You do not need to have direct contact with sheep to become infected. The key link in the chain is infected dogs. People who accidentally swallow the eggs of the Echinococcus granulosus tapeworm are at risk for infection. This happens when a dog that has eaten infected sheep or cattle organs sheds tapeworm eggs in its faeces, and a person then inadvertently ingests those eggs through contaminated hands, food, soil, water, or vegetables grown in affected soil.
This means the risk is most relevant for travellers who spend time in rural or farming communities in endemic countries, handle or play with dogs in those settings without washing their hands, or consume food or water of uncertain origin in affected regions. Tourists passing through cities on a typical holiday face very little risk.
Could I have picked this up in Australia, or is it only a concern overseas?
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Hydatid disease does occur in Australia, and is notifiable in every state and territory. The disease is present in dogs and livestock in rural sheep-raising regions across inland New South Wales, Queensland, South Australia, and parts of Western Australia. It is also present in some feral animal populations including wild pigs. Although Tasmania was declared provisionally hydatid disease-free in 1996 after more than 30 years of active control efforts, cases in non-imported dogs, sheep, and young cattle persist in northern Tasmania.
Travellers who visit or work in Australian rural areas, handle working dogs on farms, or assist with livestock slaughter should apply the same hygiene principles as they would overseas.
My doctor has found a cyst in my liver on a scan. Is it possible this has been there for years without me knowing?
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Yes, and this is one of the defining and difficult characteristics of hydatid disease. Because the cysts are slow-growing, infection may not produce any symptoms for many years.
A cyst in the liver can grow steadily over a decade or longer without causing any noticeable discomfort, and is often found incidentally during an ultrasound or scan performed for an unrelated reason. This means some people are diagnosed with a cyst that may have developed from an infection contracted many years, or even decades, earlier.
If a cyst is found and you have any history of living or travelling in a rural area of an endemic country, or of handling dogs in such settings, it is important to tell your doctor so the possibility of hydatid disease can be specifically investigated.
I was handling dogs at a farm during a recent overseas trip. What should I do when I get home?
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If you had close contact with dogs in a sheep or cattle farming area of a hydatid-endemic country, particularly if you allowed dogs to lick your hands or face and did not wash your hands thoroughly before eating, there is a small possibility of exposure. In practice, the chance of infection from a single brief exposure is low, and many travellers handle farm dogs without coming to any harm.
There is no post-exposure preventive medication available that can reliably prevent cyst development if eggs were swallowed. The appropriate step is to mention this to your GP and keep the experience in mind. The diagnosis of E. granulosus infection is suggested by identification of a cyst-like mass in a person with a history of exposure to sheepdogs in areas where the parasite is endemic.
If you subsequently develop any upper abdominal discomfort, a persistent cough, or unexplained symptoms over the months or years ahead, remind your doctor of this exposure so they can consider hydatid disease in their assessment.
Is hydatid disease contagious? Can I spread it to my family if I am diagnosed?
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Hydatid disease is not transmitted from person to person. People carrying the infection are not contagious to others. The parasite completes part of its life cycle in dogs and another part in livestock or other mammals.
Humans are what is called an accidental dead-end intermediate host, the parasite can form cysts inside a person, but those cysts cannot be passed to another person through normal contact.
If you are diagnosed with hydatid disease, your family members are not at risk from being around you. However, if you have a dog that has potentially been in contact with infected livestock organs, that dog should be checked by a veterinarian, and general hygiene including washing hands with soap and warm water after handling dogs and before handling food is an important ongoing habit for your household.
What to Know
Symptoms of Hydatid Disease
Hydatid disease often causes no symptoms for many years because the cysts grow slowly. The liver is most commonly affected (around 60–70%), where cysts may cause upper abdominal discomfort, fullness or nausea. If they affect the bile ducts, jaundice can develop.
Lung involvement accounts for around 20–30% of cases and may cause persistent cough, chest discomfort or occasionally blood-stained sputum. Smaller cysts can remain undetected for years. Cysts can also develop in the brain, heart, kidneys, spleen, bones or spine, causing symptoms specific to the affected organ.
The most serious complication is cyst rupture, which can occur spontaneously, after an injury or during a medical procedure. Leakage of cyst fluid can cause a severe allergic reaction, including potentially life-threatening anaphylaxis, and may spread parasite material, resulting in new cysts elsewhere. Sudden hives, swelling, breathing difficulty or other signs of a severe allergic reaction require emergency medical care.
Diagnosis and treatment of Hydatid Disease
Hydatid disease is usually detected through medical imaging, sometimes incidentally. Ultrasound is the preferred initial test for suspected liver cysts, while CT provides greater detail and is useful for assessing complications or disease in multiple organs. MRI is particularly helpful for assessing bile-duct involvement. Diagnosis is supported by a history of exposure to infected dogs, livestock or endemic areas, so relevant travel and animal contact should be reported to the doctor. Blood tests for parasite antibodies can support the diagnosis, although they may be negative in early or inactive disease. Suspected cases should be assessed by an infectious diseases specialist.
Treatment is tailored to the size, number, location and activity of the cysts, as well as the person’s overall health. Some cysts can be removed surgically, sometimes with additional medication to reduce the chance of the infection returning or spreading. Certain liver cysts can instead be treated through a small needle procedure called PAIR, where the cyst is drained, treated to destroy the parasite, and drained again. If a cyst leaks or ruptures, additional treatment may be needed to reduce the risk of new cysts developing elsewhere. Small or inactive cysts may not need immediate treatment and can sometimes be monitored with regular scans. When surgery or drainage is not suitable, medication may be used on its own, although it is generally less effective. Because treatment can be complex, care should involve specialists experienced in hydatid disease.
Prevention of Hydatid Disease
There is no human vaccine against hydatid disease, so prevention relies on avoiding contact with parasite eggs and interrupting transmission between dogs and livestock. Wash hands thoroughly after handling dogs and before eating, avoid letting dogs lick your face or hands, and avoid food, water, soil or uncooked produce that may be contaminated with dog faeces.
In farming areas, prevent dogs from eating raw offal or livestock carcasses, and ensure discarded animal organs are inaccessible. Farm dogs in endemic regions should receive regular veterinary deworming, and dogs that may have eaten infected organs should be assessed by a veterinarian. Control programs involving dog treatment and livestock vaccination have substantially reduced transmission in some regions.