Histopathology and Other Methods for Detection of Viral Hemorrhagic Septicemia (VHS) in Some Iranian Rainbow Trout Farms

Abstract

Viral haemorrhagic septicaemia (VHS) is one of the most economically important viral disease problems in European salmonid aquaculture (Jorgensen, 1974). It has been widely reported that VHS disease can cause mass mortality in farmed rainbow trout (Oncorhynchus mykiss) of all ages. Recently, this disease was found in rainbow trout cultured in the Pacific Ocean and also in farms rearing marine species. Several cases of VHS disease have been reported in rainbow trout breeding farms in Iran. Water temperature also plays an important role in the course of a VHS outbreak (Ahne & Thomsen, 1985), with the disease a more serious problem at water temperatures below 15-16°C (McAllister, 1979). Disease outbreaks usually occur between water temperatures of 4-14°C. The first VHS disease outbreaks occurred in Iranian aquaculture in November 2005 at Rodsar of Gilan province in the north of Iran with water temperatures measured at 10°C. Viral haemorrhagic septicaemia (VHS) is considered the most serious disease of rainbow trout in aquaculture. It can cause up to 80% mortality in affected stocks. Iran was historically free from this disease. However, in November 2005, a VHS outbreak caused high levels of mortality in Rodsar of Gilan province trout farm. This outbreak resulted in serious economic losses for many farms. Viral haemorrhagic septicaemia virus (VHSV) of the family Rhabdoviridae.VHS was first reported from a rainbow trout farm in Denmark and has since caused significant losses in rainbow trout farms in many countries in continental Europe. It has also been reported in Japan and Russia. A highly virulent new strain of VHS has been reported in a range of freshwater fish species in the USA. Viral hemorrhagic septicemia (VHS) is an acute to chronic viral disease of salmonids that causes serious economic problems in rainbow trout cultured in several European countries. Although this disease has not been detected in North America, it is included here as a disease of significant concern. The disease was first recognized by Schaeperclaus in Germany in 1938. In 1949, the disease was named Egtved disease after an outbreak in Denmark near a village of that name. In 1966, the Oftice Intematlonale d’Epizooties recommended that the name be changed to viral hemorrhagic septicemia to reduce confusion due to the names used in the various European countries where it occurs (Roberts 1978).