Pathogenesis:
Pathogenesis Encysted larval stages generally do not cause clinical disease in domestic livestock as they are often confined to visceral tissues. However, significant pathological changes occur in humans when the slowly-growing cysts put pressure on surrounding tissues and produce chronic space-occupying lesions Cysts may grow around 1 mm per month and can become extremely large, up to 30cm in diameter with litres of fluid containing thousands of protoscoleces . Organ enlargement may be accompanied by a variety of clinical signs depending on the size and location of the cysts.
Compression of liver may result in jaundice, portal hypertension and abdominal distention. Cysts in the lung may cause haemoptysis (coughing up blood), dyspnoea (difficulty breathing) and chest pain. Cysts in the brain or spinal cord can provoke acute inflammatory responses and numerous neurological sequalae , including epilepsy and blindness. Cyst rupture has been associated with acute clinical signs (such as peritonitis and pneumothorax ), and the sudden release of hydatid fluid may cause severe allergic reactions (such as asthma and anaphylactic shock). Protoscoleces released from ruptured cysts can regress and form new hydatid cysts throughout the body.