[Immunological correlations between 2 strains of mucosal disease virus diarrhea (short report].

Cross-neutralization tests of the C24V strain and the "Kotschmar" strain provided evidence that the two strains are serological variants. Independenthy of quantitative serological differences, these strains had a better immunizing action in calves against a virulent strain of MD/VD virus. This virulent strain evidently formed a third serological variant, because when calves were infected with it, there was a decrease in the serological differences between antibodies. A practical conclusion is that diagnostic serological testing using only one strain is unlikely to detect all the infected animals, particularly those with low titres of antibody. In the presence of complement the neutralizing capacity of immune serum increased and, in the case of low antibody titres, serological differences between strains decreased. Therefore the complement-dependent neutralization test with at least two strains of virus is recommended for use in diagnostics.