Effects of temperature on infectivity and of commercial freezing on survival of the North American strain of viral hemorrhagic septicemia virus (VHSV)

Temperature affected the growth of the North American strain of viral hemorrhagic septicemia virus (VHSV) in experimentally infected cell cultures and in Pacific sardine Sardinops sagax. In addition, commercial freezing significantly reduced the infectivity of VHSV in tissues of experimentally infected sardine. Isolates of VHSV representing the geographic range of North American VHSV replicated in the EPC (Epithelioma papulosum cyprim) cell line at 10, 15 and 20 degrees C, but the more northern isolates from British Columbia, Canada, demonstrated significantly reduced growth at 20 degrees C compared to VHSV from more southern locations (p < 0.001). An injection challenge of Pacific sardine with VHSV from California resulted in 66.7 % mortality at a seawater temperature of 13 degrees C compared to 6.7 % at 20 degrees C. Commercial blast-freezing of sardine experimentally infected with VHSV reduced median concentrations of virus in the kidney and spleen from 5.25 x 10(6) to 5.5 x 10(3) pfu (plaque-forming units) g(-1). Decreased growth of the California isolate of VHSV at higher temperatures following experimental infection of the sardine and reduced virus survival following commercial freezing of infected sardine are factors that would lessen the risk of transmission of VHSV through frozen baitfishes.