Echinococcosis (hydatid disease): causes, symptoms and treatment

Echinococcosis is a zoonotic disease: it passes to humans from animals. WHO describes four forms, of which the two of public health importance are cystic echinococcosis (also called hydatid disease or hydatidosis), caused by Echinococcus granulosus, and alveolar echinococcosis, caused by E. multilocularis.

Humans are accidental hosts. WHO explains that animals such as sheep, goats, cattle and pigs act as intermediate hosts, while dogs and other carnivores carry the mature tapeworm in the intestine. Humans acquire infection in the same way as intermediate hosts and do not transmit it onward to dogs.

This page relies mainly on WHO because UK-specific patient information on echinococcosis is limited. Its relevance in the UK is mainly for people who have lived in or travelled to areas where the disease is common.

WHO says infection occurs when people ingest parasite eggs, shed in the faeces of infected dogs, via contaminated food, water or soil, or by direct contact with animal hosts. The genotype causing most human cystic echinococcosis is maintained in a dog-sheep-dog cycle.

Alveolar echinococcosis usually occurs in a wildlife cycle between foxes or other carnivores and small mammals such as rodents. WHO says domesticated dogs and cats can also act as definitive hosts. Alveolar disease is confined to the northern hemisphere, including parts of continental Europe.

Prevention programmes focus on deworming dogs, slaughterhouse hygiene and public education, according to WHO.

WHO says the incubation period can last many years, and that symptoms depend on where cysts are and the pressure they place on surrounding tissue.

• Liver cysts: abdominal pain, nausea and vomiting.

• Lung cysts: chronic cough, chest pain and shortness of breath.

• Non-specific signs such as loss of appetite, weight loss and weakness.

• Alveolar echinococcosis: weight loss, abdominal pain, general malaise and signs of liver failure, with a slowly growing tumour-like lesion that WHO says is usually in the liver.

• No symptoms for many years in many people; cysts are sometimes found incidentally on imaging.

See a GP if you have persistent upper abdominal pain, a persistent cough or breathlessness, or unexplained weight loss, particularly if you have lived in or travelled to a region where hydatid disease is common. Tell the doctor about travel history and contact with farm dogs or livestock, as this guides testing.

The NHS advice on worms in humans, which applies to tapeworm infections generally, says infections can take a long time to cause symptoms, and to tell the GP if you have been abroad in the last 2 years. Sudden severe abdominal pain, collapse, a rash with breathing difficulty or sudden severe breathlessness need 999 or A&E.

WHO says ultrasonography is the technique of choice for diagnosing both cystic and alveolar echinococcosis, usually complemented or validated by CT or MRI. Cysts can be discovered incidentally on radiography. Specific antibodies are detected by serological tests and can support the diagnosis.

WHO also says the choice of treatment must primarily be based on the ultrasound images of the cyst, following a stage-specific approach, which is why imaging is repeated and interpreted by experienced radiologists.

WHO says both cystic and alveolar echinococcosis are often expensive and complicated to treat, sometimes requiring extensive surgery and/or prolonged drug therapy. For cystic echinococcosis there are four options, chosen on the ultrasound appearance of the cyst and the resources available.

WHO says early diagnosis and radical, tumour-like surgery followed by anti-infective prophylaxis with albendazole remain the key elements of treatment for alveolar echinococcosis. If the lesion is confined, radical surgery can be curative.

Unfortunately in many patients the disease is diagnosed at an advanced stage, and palliative surgery without complete anti-infective treatment is followed by frequent relapses. If left untreated, alveolar echinococcosis is progressive and fatal, according to WHO.

In the UK, suspected echinococcosis is investigated through the GP, then imaging and a gastroenterology, hepatology, respiratory or infectious diseases and tropical medicine team. Treatment decisions are made by specialist multidisciplinary teams.

Private infectious diseases consultations can speed assessment, but complex surgery and long-term drug therapy need experienced specialist centres, and the GP should be kept informed.