Echinococcosis (Hydatid Disease)

What echinococcosis is

Echinococcus tapeworms live as adults, only a few millimeters long, in the intestines of dogs, foxes and wolves. Their eggs pass out in feces. Sheep, goats, cattle and other grazing animals swallow the eggs and develop cysts in their organs. Dogs are reinfected when they eat raw offal from these animals.

Humans are accidental hosts. When a person swallows eggs, the larvae hatch in the gut, pass into the bloodstream and settle in organs, where they grow into cysts. Infection cannot pass from one person to another.

Two forms cause almost all human disease:

Symptoms

Most people have no symptoms for 5 to 15 years or longer while a cyst slowly grows. Symptoms depend on the cyst's size and location.

Liver cysts

• dull pain or a feeling of fullness under the right ribs
• an enlarged liver or a mass you can feel
• nausea and loss of appetite
• jaundice if a cyst presses on or opens into the bile ducts, sometimes with fever and chills from infected bile

Lung cysts

• chronic cough and chest pain
• breathlessness
• coughing up blood
• coughing up salty fluid or pieces of white membrane (sometimes described as "grape skins") if a cyst ruptures into an airway

Other sites

Cysts can occasionally form in the spleen, kidneys, bones, heart, brain or eyes, causing problems linked to pressure on those organs.

Alveolar echinococcosis

This behaves like a slow-growing liver cancer, with weight loss, pain and jaundice. It can spread to nearby organs, the lungs and the brain.

Complications

• Rupture: a cyst can burst after injury or during surgery. Cyst fluid can trigger anaphylaxis, a severe allergic reaction, and seed new cysts.
• Infection of the cyst, forming an abscess.
• Bile duct blockage and cholangitis (infected bile ducts).
• Pressure damage to nearby organs and blood vessels.

How it is diagnosed

• Ultrasound: the main test for liver cysts. The World Health Organization classifies cysts from CE1 to CE5 based on their appearance. Active cysts (CE1 and CE2) contain living parasites; calcified cysts (CE5) are usually inactive.
• CT or MRI: for lung cysts, complex liver cysts, cysts elsewhere, and planning treatment.
• Blood antibody tests: support the diagnosis, but a negative result does not rule it out, especially for lung cysts.
• Chest X-ray: shows round lung cysts.

Doctors avoid needling a suspected hydatid cyst for diagnosis unless it is done as part of planned treatment, because leaking fluid can cause anaphylaxis or spread.

Treatment

The choice depends on the cyst's stage, size, site and the facilities available.

• Albendazole: an antiparasitic tablet taken for months. It can cure small cysts on its own and is given before and after any procedure to prevent spread.
• PAIR: Puncture, Aspiration of the fluid, Injection of a scolicidal agent (such as hypertonic saline or alcohol), and Re-aspiration, all under ultrasound guidance. It suits many liver cysts.
• Surgery: to remove complicated, large, infected or lung cysts. Lung cysts are usually treated surgically.
• Watch and wait: inactive, calcified cysts that cause no symptoms are often just monitored with periodic ultrasound.
• Alveolar disease: radical surgery to remove the affected liver plus albendazole for at least 2 years, often lifelong if the disease cannot be fully removed. Liver transplantation is an option in selected cases.

Follow-up scans continue for several years, because cysts can recur.

Outlook

Cystic echinococcosis is usually curable, especially when found early. Recurrence after surgery happens in a minority of people. Alveolar echinococcosis is more serious, but long-term albendazole and surgery have greatly improved survival. Without treatment it is usually fatal within about 10 to 15 years.

Prevention

• Deworm dogs regularly with praziquantel in endemic areas.
• Do not feed dogs raw offal from slaughtered sheep, goats or cattle.
• Wash hands after handling dogs or working with soil.
• Wash fruits and vegetables, especially wild berries in fox areas, and drink safe water.
• Support safe slaughter practices that dispose of infected organs.

Frequently asked questions

How do humans get echinococcosis?

By swallowing tapeworm eggs passed in the feces of infected dogs, foxes or wolves. Eggs reach the mouth from contaminated hands after touching a dog's fur or soil, or from unwashed vegetables, berries or water. It does not spread from person to person, and eating meat does not infect humans.

What is a hydatid cyst?

A hydatid cyst is the fluid-filled larval stage of the Echinococcus granulosus tapeworm. It has a tough outer layer and contains thousands of tiny tapeworm heads (protoscolices). Cysts grow slowly over years, usually in the liver or lungs, and can reach several inches across.

Is hydatid disease curable?

Cystic hydatid disease is usually curable with albendazole, PAIR drainage, surgery or a combination. Inactive cysts often need no treatment beyond monitoring. Alveolar echinococcosis is harder to cure but can often be controlled with surgery and long-term albendazole.

What are the symptoms of a hydatid cyst in the liver?

Many liver cysts cause no symptoms. As they grow they can cause dull upper right belly pain, fullness, nausea and an enlarged liver. A cyst that blocks bile ducts causes jaundice, and a ruptured cyst can cause sudden pain and a severe allergic reaction.

Is echinococcosis found in the United States?

It is rare in the US. Most cases are diagnosed in people who lived in endemic countries. Small numbers of local cases have occurred in Alaska, the western states and areas where dogs are fed sheep offal, and E. multilocularis is found in some foxes in northern states.