Abstract
Ibaraki virus (IBAV) prevailed on certain dairy farms between June 1997 and March 1998. During that time, surveys were conducted among un-inoculated dairy cows (24-28) and inoculated dairy cows (24-27) to determine the presence of neutralizing antibodies to the epizootic strain 97MD70 and non-epizootic strain No.2. In September and October, positive antibody rates for both strains were high. Neutralizing antibody titers to both the 97MD70 and No.2 strains were significantly lower in inoculated cows than un-inoculated cows (P<0.01). Epidemiological investigations conducted on serum samples collected from cattle spending the first summer seasons of 1997 and 1998 in the region showed neutralizing antibody titers to the No.2 strain to be significantly lower than titers to the 97MD70 strain (P<0.01). Among examples surveyed periodically, a maximum of 40 out of 99 (40.4 %) samples obtained in September 1997 was antibody-positive to the 97MD70 strain but negative to the No.2 strain. These findings suggest that the epizootic strain should be used in neutralization test with IBAV for serological survey.
