IBARAKI VIRUS, AN AGENT OF EPIZOOTIC DISEASE OF CATTLE RESEMBLING BLUETONGUE .2. ISOLATION OF VIRUS IN BOVINE CELL CULTURE

Several strains of a virus, designated as Ibaraki virus, were isolated in bovine cell cultures from natural and experimentally produced cases of the disease. In some of these cases, antibody titer rises were shown against Ibaraki virus. The clinical materials used for virus isolation induced in calves a mild illness similar to the natural disease, as well as neutralizing antibody against Ibaraki virus. Antibody titer rises were also shown in a high percentage of natural cases clinically diagnosed as having the disease. Antibody was not detected in any of the cattle in non‐epizootic areas, while many cattle in the epizootic areas had antibody after the outbreak. In the epizootic areas the antibody incidence after the outbreak was much higher among cattle diagnosed as having the disease during the outbreak than those not affected. These results leave little doubt that Ibaraki virus is the etiologic agent of these disease. Ibaraki virus became less virulent for calves upon serial passage in bovine cell cultures. The bovine cell cultures appeared less sensitive than the calf inoculation for the primary detection of the virus. The use of intermediary calf inoculation before inoculation into tissue culture may improve the isolation rate, but the tissue culture technique itself should be improved as calf inoculation is both expensive and cumbersome. © jointly owned by Japanese society for Bacteriology and Society of Japanese Virologists