Emergence and resurgence of the viral hemorrhagic septicemia virus (Novirhabdovirus, Rhabdoviridae, Mononegavirales)

Viral hemorrhagic septicemia virus (VHSV) is one of the most serious pathogens of finfish worldwide in terms of its wide host-range, pathogenicity, disease course, and mortality rates. The disease was first documented in the 1930s in Europe in association with heavy losses in rainbow. Data collected over 50 years show that VHSV is a virus of marine origin: its ability to alternate between marine and freshwater environments remains an enigma which requires further investigation. In 2003, VHSV invaded the Laurentian Great Lakes basin causing devastating losses. VHSV is believed to have negative impacts on a number of important Atlantic, Pacific, and Great Lakes fish species. Phylogenetic analysis has offered clues into the geographic and host range of the virus, but sporadic outbreaks of the disease in uncommon locations have imparted unforeseen challenges in delineating the virus’ regional distribution. The virus’ ability to gain access to aquaculture farms has also positioned it as a disease of utmost priority once detected in these settings. Current diagnostic methods, while greatly improved, are hampered by the variability of disease course among susceptible species. In general, VHSV causes severe degeneration in the hematopoietic tissues of affected fish. Based on historical and current data, it is feared that VHSV will continue to mutate, expand to other geographic areas, and infect new host species. As a result, immediate international attention and coordination of efforts are needed. The objective of this review article is to provide an updated synopsis on the current status of VHSV epizootiology and pathogenicity.