It is also an obligate intracellular organism and has been culture in 6 different cell lines. Characteristic CPE include cell rounding and development of one or more large vacuoles within the cytoplasm of the host. Four of the six susceptible cell lines come from salmonid species. The other two lines come from warm water fish species. However, it has been reported that many heavily infected fish show no external lesions.
Internal lesions are very characteristic of the disease.
Commonly infected organs are liver, spleen, intestine, and hematopoietic tissue of the kidney. The most characteristic internal lesions are off-white to yellow nodules measuring up to 2 cm in diameter throughout the liver. Click here to see picture P. salmonis a wide variety of cells including macrophages. Within the cell they replicate in membrane bound intracytoplasmic vacuoles of variable size. It has also been found extracellularly, apparently as a result of cell lysis.