Tissue reaction to spherical and lobular hydatid cysts of Echinococcus granulosus (Batsch, 1786).

We have studied the tissue reaction to spherical and lobular cysts of Echinococcus granulosus (Batsch, 1786) on a set of 108 observations of hydatidosis in the liver and lung of pigs. Typical of an early response of the host to a growing hydatid cyst is a local allergic inflammation characterized by a heavy infiltration of eosinophiles. If the infection is massive, sensitization increases the tissue reaction, and there is a marked exudation of eosinophiles into the pseudocyst which results in the ultimate death and liquidation of the parasite. In an organ infested with lobular and multilobular hydatid cysts, this early type of a tissue reaction persists around pouches in the hydatid wall. Typical of this reaction is an epitheloid rim, a new production of connective tissue, and an inflammatory infiltration. In fertile, large-sized cysts, the acute inflammatory reaction disappears from the inner side of the connective tissue sheath, and the wall of the hydatid remains in a direct contact with a thick layer of hyalinely degenerated, fibrous, connective tissue. A moderate, chronical, infiltrate along the periphery of the encapsulation provides evidence for a balanced relationship between the parasite and its host.