Study on clinical and gross pathology manifestation of Viral HemorrhagicSepticemia (VHS) disease in cultured rainbow trout (Oncorhynchus mykiss) in Iran (2013-2015)

Viral Hemorrhagic Septicemia (VHS) is an acute viral disease leads to great losses in farmed rainbow trout (Oncorhynchus mykiss). The disease has three different clinical forms including acute, chronic and nervous with different clinical and necropsy signs. This research  was conducted in Iran from 2013 to 2015 in 2641 rainbow trout farms (Hatcheries and fish farms) in order to describe the gross pathology pattern of this disease. The observed signs in the present study were categorized into the five different groups including group 1 with general signs of septicemia, group 2 with hemorrhagic signs, group 3 with nervous signs, group 4 with anemia signs and group 5 with high mortality. All infected farms were inspected and clinical and necropsy signs and mortality rate were recorded based on the designated forms and registered in Geographical Information System (GIS) of Iran veterinary organization (the electronic system for surveillance and monitoring of animals). Results of each year were evaluated descriptively and analytically using chi square test. The dominant group based on the registered signes during 3 years of survey was mortality in 2013, general signs of septicemia in 2014, and general signs of septicemia in 2015. The observed frequency of signs were highest for the general septicemia group and lowest for the anemia group during three years of study. According to the results of the present study, it seems that VHS gross pathology pattern in Iran has been changed from acute manifestation to the chronic form. As the general signs common to a number of diseases, it is so important for clinicians to consider VHS in their differential diagnosis lists.