Echinococcosis

Etiology and the parasite's pathway in the body

The life cycle of the causative agent involves two hosts. Intermediate hosts are farm animals (sheep, cows, pigs), which harbor the cystic form. Definitive hosts are carnivores, such as dogs and wolves, in whose intestines the adult parasite lives. Human infection occurs through close contact with infected dogs.

Upon entering the human body, the helminth eggs undergo a complex migration pathway:

1. In the intestine, the egg loses its protective coat.
2. The embryo penetrates through the intestinal wall into the bloodstream.
3. Via the portal venous system, it reaches the liver. This is the primary barrier where the vast majority of larvae (up to 70%) settle.
4. Once past the hepatic filter, the larva enters the lesser circulation and reaches the lungs, where up to 15% of cysts are formed.
5. Having overcome the lungs, the parasite enters the systemic circulation and can settle in any organ (kidneys, brain, muscles, bones).

Morphology of the echinococcal cyst

Having fixed in the tissue, the embryo sheds its hooks and transforms into a bladder (hydatid form). The cyst grows extremely slowly, sometimes for decades, reaching giant sizes (15–20 cm).

The structure of the cyst includes several layers:

• Germinal layer (inner) — actively functioning tissue. This is where scoleces (parasite heads) and daughter cysts are formed. Granddaughter cysts may form inside the daughter cysts. The number of scoleces can reach thousands.
• Chitinous membrane — a dense acellular layer that holds the clear fluid of the cyst.
• Fibrous capsule (outer) — this is the host organism's reaction. Tissues around the parasite undergo aseptic productive inflammation, forming a dense barrier that may calcify over time.

Slowly enlarging, the cyst compresses neighboring organs, causing their atrophy.

Stages of the disease and clinical presentation

The disease lacks strictly specific symptoms and remains latent for a long time.

Stage I — Asymptomatic. It starts from the moment of parasite introduction until the appearance of the first complaints. The duration depends on the localization: in the liver and lungs, it is measured in years, whereas in the brain or eye, symptoms appear much faster.

Stage II — Clinical manifestations. Associated with cyst growth and mechanical pressure on tissues.

• Pain syndrome: occurs due to stretching of organ capsules (e.g., Glisson's capsule of the liver) or the pleura.
• General manifestations: weakness, nausea, allergic reactions (skin itching, urticaria).
• Objectively: organ enlargement (hepato- or splenomegaly) or a painless protrusion can be palpated.

Stage III — Complicated. The most frequent complication is suppuration of the cyst. The patient experiences a sharp spike in temperature (hectic fever up to 41 °C), chills, profuse sweating, and signs of severe intoxication. The second formidable complication is cyst rupture into hollow organs, a bronchus (expectoration of sputum containing parasite membranes), the abdominal or pleural cavity. This causes an acute pain syndrome (up to shock), peritonitis, and massive dissemination of the cavities with scoleces.

Diagnostics and treatment principles

Diagnostics is based on collecting an epidemiological history (living in endemic areas, contact with dogs) and instrumental methods:

• Ultrasound reveals fluid formations. The "snowstorm sign" — visible movement of small bubbles inside the cyst — is considered specific.
• Radiography and CT help visualize the multichambered nature of the cyst, fluid levels, or calcification of the fibrous capsule.
• Laboratory findings: eosinophilia in the blood is characteristic (increases after palpation) and a positive Casoni intradermal test (redness and edema upon administration of the diagnosticum).

Treatment is strictly surgical. The main goal of surgery is to remove the parasite without allowing tissue dissemination. The optimal option is echinococcectomy (enucleation of the cyst along with the fibrous capsule) or resection of the affected organ segment. If complete removal is impossible, echinococcotomy is performed: the cyst is opened with careful isolation of the operative field, the contents are removed, and the chitinous membrane is excised. The cavity must be treated with antiparasitic solutions (formalin, hypertonic NaCl solution), after which it is drained or sutured (capitonnage).

Briefly: answers to topical questions

What else to study on this topic

• Technique of echinococcotomy: stages of capitonnage and antiparasitic treatment
• Differential diagnosis of an echinococcal cyst and a liver abscess
• Features of the clinical presentation in bone tissue involvement (pathological fractures)
• Interpretation of radioisotope scanning: "cold spots"
• Casoni reaction: indications, procedure, and causes of false-negative results

Other topics in the section "CHAPTER 15. PARASITIC SURGICAL DISEASES"

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