Review • DS Provotorov, SA Murzina, EP Ieshko, NN Nemova • Journal of General Biology • Issue 2 • Volume 83, 2022

Ulcerative salmon skin necrosis (UDN) is a disease of mature salmon that is characterized by massive mortality. It is accompanied by the formation of skin ulcers, which are further affected by secondary pathogens. The disease has been recorded since the 19th century. In recent years, an increase in the frequency of salmon has been reported from Sweden, Finland, Russia and other European countries. At the same time, only half of the fish with UDN-like lesions have been diagnosed with UDN, and given the new symptoms, a new UDN-like disease is now being isolated – “Red Skin Disease”. Attempts have been made since the 1960s to pinpoint the cause of UDN. Researchers have found virus-like particles in the tissues of infected fish, but the origin and role of these particles remain unknown and their viral nature has not been confirmed. In recent years, the main focus has been on studying the effects of UDN on the body of salmon. The hematological and biochemical parameters of infected individuals are studied, an increase in the level of urea in infected fish, osmotic hemodilution, a decrease in the concentration of total plasma protein and albumin and a violation of carbohydrate metabolism have been observed. However, there is still very little data on the origin, etiology, pathogenesis of UDN, therefore, it is necessary to expand complex interdisciplinary research, which will allow us to develop effective measures to combat this disease and to offer a system monitoring and forecasting further status and stocks of Atlantic salmon populations.

Ulcerative dermal necrosis (UDN) is a serious disease of mature salmon fish, characterized by massive mortality of infected individuals. Necrosis is accompanied by the formation of skin ulcers, which are then affected by secondary pathogens (for example, fungi p. Saprolegnia or various pathogenic bacteria), which eventually leads to death. This disease was recorded in the 19th century under the name “salmon disease”. It then occurred intermittently until the mid-1960s, when the infection spread to southwestern Ireland and spread further to the rivers of the British Isles and neighboring countries. Currently, salmon cases vary by season and region. In recent years, there have been reports of an increase in the frequency of salmon from various countries, such as Sweden, Finland, Russia and others. It should be noted that only half of the fish with UDN-type lesions were specifically diagnosed with UDN based on all diagnostic criteria for this disease. Given this fact, and also considering the discovery of new symptoms in infected fish, including red spots on the skin, including abdominal rash, skin bleeding, a new disease is identified – red skin disease (RSD), which its diagnostic criteria along with the UDN. The decision to register a new disease and approve its name was taken at a scientific seminar in November 2019 at the Norwegian Institute of Nature (NINA, Norway).

Attempts have been made since the 1960s to pinpoint the cause of UDN. Thus, the main efforts in a series of experiments were made to elucidate the ways and mechanisms of transmission of an infectious agent in water. Using a light and electron microscope, it was found that in fish in all ulcers were found numerous virus-like particles with a diameter of 30 to 33 nm. At the same time, the size and shape of the particles are consistent with those for β-glycogen particles, which has led to ambiguous interpretations and conclusions about the source of the disease. The origin and role of these particles remain unknown, their viral nature has not been confirmed. Although most researchers believe that the nature of the disease is viral, there is no clear scientific evidence for this.

In recent years, the main focus has been on the study of the effects of UDN on the body of salmon reproducers: the hematological and biochemical parameters of infected individuals are studied, which, in turn, can lead to an understanding of the mechanisms of action of the disease and contribute to development of preventive or therapeutic drugs. In these studies, an increase in the level of urea in the affected fish was found, which indicates the development of dysfunction of the gill apparatus, as a significant part of the urea in the fish is excreted through the gills. It has been found that uncontrolled absorption of water caused by a violation of skin integrity (osmotic hemostasis) leads to a reduction in hematological parameters, such as, for example, the concentration of total plasma protein and albumin, which are involved in the maintenance of normal life. It has been noted that osmotic haemorrhage caused by skin violation plays an important role in the pathogenesis of the disease. In addition, in the case of UDN and RSD in Atlantic salmon, there is a disturbance in the metabolism of carbohydrates, especially glucose.

Given the fact that so far there is little convincing evidence for the origin, etiology, pathogenesis, possible consequences of this dangerous disease, it is necessary to expand comprehensive interdisciplinary research using modern experimental and informational methods, which, ultimately, will enable the development of effective measures to combat this disease and propose a system for monitoring and forecasting the further status and stocks of Atlantic salmon populations.

Leave a Comment