Echinococcosis: Parasite Life Cycle, Types of Involvement, and Signs of the Disease

The diagnosis of "echinococcosis" sounds like something out of a parasitology textbook, and that is almost true: the disease is classified among the neglected ones. Let us sort out, without panic, what this parasite is, how it lives, and why a cyst is sometimes found by chance on ultrasound.

What Echinococcus is and how its life cycle works

Echinococcosis is a parasitic disease caused by tapeworms of the genus Echinococcus. Two forms are medically significant: cystic echinococcosis (hydatid disease) from Echinococcus granulosus and alveolar echinococcosis from E. multilocularis. The sexually mature worm lives in the small intestine of the definitive host — dogs, foxes, and other canids. Intermediate hosts — sheep, pigs, cattle, rodents — become infected by eating eggs with grass and water. Humans are an accidental intermediate host: they acquire eggs through contaminated food, water, or soil, or through direct contact with animals, but do not transmit the infection further.

Who is at risk

Risk is associated with contact with infected animals (hunting and farm animals are named as the primary source of infestation), with gathering berries and herbs, and with drinking water from sources contaminated with parasite eggs. Cystic echinococcosis occurs on every continent except Antarctica; alveolar echinococcosis occurs in the Northern Hemisphere.

Which organs echinococcosis affects besides the liver

Cysts most often form in the liver and lungs, less often in bones, kidneys, spleen, muscles, and the central nervous system. Lung involvement occurs in approximately 20–30% of echinococcosis cases. The alveolar form produces a tumor-like lesion usually in the liver, and larval metastases may spread to the spleen, lungs, and brain.

• Liver — the most common localization, up to 50–70% of cases
• Lungs — about 20–30%
• Less often bones, kidneys, spleen, muscles, brain
• The alveolar form can metastasize to distant organs

Asymptomatic course and signs of hepatic echinococcosis

The incubation period of the cystic form can last for years until the cyst grows large enough to cause symptoms. With liver involvement, heaviness and pain in the right upper quadrant and epigastrium, nausea, and vomiting appear. With lung involvement — chronic cough, chest pain, shortness of breath. Nonspecific signs include loss of appetite, weight loss, and weakness. The alveolar form can remain silent for 5–15 years.

Why cyst rupture and other complications are dangerous

Rupture of an uninfected cyst is accompanied by allergic reactions, up to anaphylactic shock. Suppuration of a liver cyst produces a picture of abscess, and rupture into the bile ducts produces purulent cholangitis with jaundice and fever. Rupture of a lung cyst into a bronchus is accompanied by paroxysmal cough with sputum and blood and shortness of breath; into the pleural cavity — by acute chest pain, chills, and fever. Alveolar echinococcosis without treatment progresses and can be fatal.

The mere presence of a cyst is not a reason to call an ambulance. Call 103 or 112 for severe shortness of breath or bluish skin, severe acute chest pain, or signs of a severe allergic reaction (anaphylactic shock) after a possible cyst rupture.

Ultrasound, CT, and tests when echinococcosis is suspected

The method of choice is ultrasound, supplemented by CT and MRI. A cyst is sometimes found by chance on radiography. Serological tests detect specific antibodies and support the diagnosis. The decision on management is then made by the physician: options include observation, percutaneous treatment, surgery, and drug therapy.

This material is for reference and does not replace consultation with a physician.

This content is for reference and does not replace a doctor's consultation. Medical disclaimer