According to Ruth Torill Kongtorp a new disease called heart- and skeletal muscle inflammation (HSMI) is a serious infectious disease of farmed Atlantic salmon, with a high potential for transmission. In recent years there is increase in the number of outbreaks of this disease which indicates that it poses a significant threat to Norwegian salmon farming. It is informed that HMSI, discovered in 1999, has been found in disease outbreaks at many fish farms along the entire Norwegian coastline. In her doctorate thesis, Kongtorp described the disease and compared the pathological findings to those of a number of known diseases such as pancreas disease (PD) and cardiomyopathy syndrome (CMS). Research results show that HMSI is a new disease caused by an unknown organism. Kongtorp and her colleagues also probed the progression of the disease in field and infection trials. HMSI primarily produces inflammation and cell death in the heart. This damage arises early on in the disease, and can continue for many months. The earliest changes found were inflammatory cells lining the blood vessels of the compact heart muscle layer, and in the lining layers of the heart muscle (the epicardium outside the heart and the endocardium inside). It is also told that HSMI produces heart changes in nearly 100% of affected fish. In this phase, inflammation and cell death spread to the red skeletal muscles, cell death to the liver, and oedema (swelling) and disturbed blood circulation to multiple organs of many fish.
