Hyatid cysts
This type of disease is a parasitic infestation by a tapeworm known as ‘echinococcus granulosus’. This parasite, which lives mainly in dogs, enters your body as larvae. This is likely to happen when you handle an infested animal or eat food or drink water contaminated by its faeces. The larvae travel in the bloodstream and lodge in organs to form cysts. The liver is most commonly affected (70% of hydatid cysts form there), followed by the lungs, brain and bones.
The cysts become larger and in some cases form a mass. This can take decades, and not all cysts are active. Growing cysts can cause damage to your body tissues either directly or by affecting the flow of blood. They can also rupture or leak, possibly leading to allergic reaction and shock (anaphylaxis). If the rupture affects biliary ducts, cholangitis may follow. More seriously, secondary infection can occur if this happens in your lungs. A ruptured cyst will also cause the disease to spread further in your body.
Hydatid cysts are very rare in the UK and are more likely to be contracted abroad where there has been contact with sheep dogs and other animals. These areas are more commonly southern Europe, the Middle East, Australia, New Zealand and South America.
A related parasite, echinococcus multilocularis, is found in the northern hemisphere. It lives in wild foxes and is passed on through contact with rodents. It enters the human body in the same way as echinococcus granulocus but the cyst behaves more like a cancerous tumour.
Both parasites can cause severe liver disease but are very rare. They are estimated to affect only one person in 100,000 in the UK.
Symptoms may be at fi rst general and can be non-specific. They are generally caused by pressure from the size of the cysts. Possible symptoms may include:
Because the parasite grows slowly in your body it is rarely diagnosed during childhood or adolescence unless your brain is affected. Diagnosis of hydatid disease is usually reached by blood tests and imaging tests.
Liver function tests are used, together with a test mainly in immunology to detect the presence of antigens or antibodies, known as the enzyme-linked immunosorbent assay (ELISA). Antigens are invading or foreign proteins, and antibodies are the proteins your body produces to defend against them.
CT and ultrasound scans are most commonly used to show single or multiple cysts. MRI scans may be used to provide greater detail to help doctors decide whether cysts are active, inactive or something in between (transitional). ERCP may be used to show cysts in the bile ducts.
Drugs are usually used first in the treatment of hydatid disease to help prevent any spread of the disease although surgery is still required in many cases. The fi rst line drug treatments are albendazole and mebendazole. These drugs are given in oral form and work by being absorbed through the cyst’s membrane to affect its growth. You will have to take these drugs for three months. Another drug, praziquantel, can be given over 14 days and is now sometimes used in combination with albendazole and mebendazole.
Between a third and half of cysts treated with drugs may grow smaller or disappear. If surgery is required, the aim is usually to remove the cyst completely. This can be complicated, particularly where there has been secondary infection from the cyst, and in certain cases may carry significant risk of mortality.