Histopathology of Sanguinicola inermis infection in carp, Cyprinus carpio.

The histopathological response of carp to Sanguinicola inermis was investigated by serial sectioning laboratory infected fish up to 90 days post infection (d p.i.). Juvenile flukes and adults caused mechanical damage to tissues during invasion and migration up to 28 d p.i. Adults partially occluded blood vessels and may have reduced blood circulation. In the initial phase of egg production (28-42 d p.i.), eggs and emigrating miracidia in gill tissue caused breakdown of vascular integrity, necrosis, hyperplasia, haemorrhage and eosinophilic infiltration of epithelial tissue. After 42 d p.i. the host granulomatous inflammatory response encapsulated eggs lodged in the gills, visceral sites and connective tissue displacing normal tissue. Encapsulation and subsequent degradation of eggs and miracidia within granulomata was highly developed by 90 d p.i. Laboratory infections of S. inermis can induce respiratory distress and therefore impair respiration of fish. The parasite also caused pathological changes in osmoregulatory, excretory and haemopoietic tissue and may impair function in these organ systems.