Elimination of Genital Vibriosis in Female Cattle by Systemic Immunization with Killed Cells or Cell-Free Extracts of Campylobacter fetus

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Abstract
Heifers infected in the genital tract with Campylobaeter fetus subspecies fetus were immunized twice with killed cells or cell-free extracts in Freund's incomplete adjuvant to compare the effectiveness of the vaccines in eliminating infection with homologous and heterologous strains, to determine the incidence of antigenic variation in C. fetus, and to assess the relation of antibodies in serum and vaginal mucus to termination of infection. Cell-free vaccines, composed of a water extract rich in the antiphagocytic antigen and a crude “ribosomal” extract, were as effective as whole cells. Infection was terminated in most animals, whether infected with the homologous or a heterologous strain, one to six weeks after the first immunization. Most isolates derived two or more weeks after initiation of infection varied antigenically from the infecting strains, as measured by agglutination, precipitation, and opsonization reactions. No remarkable differences existed between heifers that were cured and those that were not cured in content of agglutinins, precipitins, or opsonins in serum or vaginal mucus, or in the incidence of antigenic variants. These studies demonstrate the success of systemic immunization with subcellular fractions of bacteria in eliminating a localized genital infection. The emergence of antigenic variants has been confirmed as a general consequence of C. fetus infection. No relation could be established between cure of infection and qualitative or quantitative measures of local and systemic humoral immune responses.