Observational study of erythrocytic inclusion bodies in farmed Atlantic salmon, Salmo salar L., in the British Isles

An observational study was conducted of farmed Atlantic salmon, Salmo salar L., in the British Isles with regard to intraerythrocytic inclusions and disease prevalence. Intraerythrocytic inclusions were observed to be widespread in Atlantic salmon from farms in Ireland and Scotland. The percentage of fish infected with these inclusions and the intensity of infection were greater in sea stage salmon than those in fresh water. This corresponded with reduced values for haematological parameters (haematocrit, erythrocyte count, haemoglobin, MCV, MCH, MCHC). There appeared to be a significant association between the presence of the intraerythrocytic inclusions and focal cardiomyopathy, although there was no established association with overt clinical disease and the presence of the inclusions. There was also a significant association between the presence of raised splenic haemosiderin and multiple intraerythrocytic inclusions.