The disease occur worldwide and at least 97 species of teleostfishes are known to be affected. Pathological changes are confined to the erythrocytes leading to serious anemia. It is beleived the disease is caused by a member of iridoviridae based on the morphology and presumed DNA genome. The virus was isolated from the skin on a sturgeon cell line and described by Hedrick et al. The virus infects the skin and gills and infected cells expand and migrate from the epithelium.
Mortality is caused by secondary infections of bacteria and protozoa.
The virus has been found in fish from many facilities. Disease is most severe in young fish and survivors of infections are the possiblities of carriers. Residual viral infectivity was found following incubation of the virus at a temperature of 56 degree C for 30 min. In Oregon, WSIV was consistently detected in young sturgeon that were progeny from Columbia River adults and cultured in river water but not detected in sturgeon cultured in well water. In Idaho, WSIV was detected in sturgeon that were progeny from wild Snake River and Kootenai River adults after being subjected to stressful conditions of low spring water flows and high fish densities.