Pathogenesis and Clinical Manifestations of Human Cystic Echinococcosis Cystic echinococcosis, commonly known as hydatid disease, is a parasitic disease caused by the larval stage of Echinococcus granulosus. The disease is characterized by the gradual development of hydatid cysts in various human organs. The severity of infection depends mainly on the location, size, and growth of the cysts and their effects on surrounding tissues. The liver is the most frequently affected organ. As hydatid cysts enlarge, they may compress the hepatic tissue, bile ducts, and adjacent blood vessels. This pressure can cause right upper abdominal pain, hepatomegaly, and, in some cases, jaundice due to obstruction of the bile ducts. Local inflammatory and fibrotic reactions may also develop around the cyst as the body's tissues respond to its presence. The lungs are the second most commonly affected organs. Pulmonary hydatid cysts may compress the surrounding lung tissue and interfere with normal respiratory function, resulting in cough, chest pain, and shortness of breath. Large cysts may cause damage to adjacent tissues, while rupture into the bronchi can lead to serious respiratory complications. Hydatid cysts may also develop in other organs, including the brain, kidneys, spleen, and bones. Their pathological effects vary according to the affected organ. In the brain, cyst growth may increase intracranial pressure and produce neurological manifestations. In bones, the cysts may progressively damage bone tissue, weaken its structure, and increase the risk of pathological fractures. The principal mechanism of tissue damage is the mechanical pressure exerted by the enlarging cyst rather than direct invasion of host cells. A fibrous capsule and inflammatory response may develop around the cyst, although their extent varies between cases. Cyst rupture is a particularly serious complication because the release of cyst contents may lead to secondary cyst formation and severe allergic reactions, including anaphylaxis. Clinical manifestations may remain absent for several years because hydatid cysts usually grow slowly. Symptoms generally appear when the cyst becomes sufficiently large to affect the function of the involved organ or when complications develop. Diagnosis relies mainly on medical imaging, particularly ultrasonography, computed tomography (CT), and magnetic resonance imaging (MRI), with serological tests used as supportive investigations when appropriate. Treatment depends on the cyst's location, size, and stage and may include clinical monitoring, antiparasitic medication, percutaneous procedures, or surgery. Conclusion Human cystic echinococcosis is an important parasitic disease because hydatid cysts can progressively impair organ function and cause serious complications. Understanding the pathogenesis and clinical manifestations of this disease is essential for evaluating its severity, establishing an accurate diagnosis, and selecting appropriate treatment.