OBSERVATION OF A RICKETTSIA-LIKE ORGANISM IN ATLANTIC SALMON, SALMO-SALAR L, IN IRELAND

A rickettsia-like organism was observed in tissues of farmed Atlantic salmon, Salmo salar L., experiencing mortalities in the West of Irelan d. Gross pathology of affected fish included haemorrhages in the skele tal muscle, splenomegaly, congestion of pyloric caeca and yellow mottl ing of livers, which appeared in ring formations in some cases. Histop athology was most obvious in the spleens, livers, kidneys and hearts, with widespread tissue necrosis and numerous basophilic granules prese nt in the cytoplasm and cytoplasmic vacuoles of a variety of cells. Tr ansmission electron microscopy revealed micro-organisms within membran e-bound cytoplasmic vacuoles similar in appearance to rickettsia.