Submitted to: Poultry Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/1/1996
Publication Date: N/A
Interpretive Summary: Pullorum disease, a severe systemic infection of poultry that can be transmitted vertically to the progeny of infected breeding stock, caused significant mortality losses in young chickens until the implementation of a control program based on testing commercial breeding flocks for antibodies to the causative agent, Salmonella pullorum. In some recent pullorum disease outbreaks in commercial chickens, however, the standard antibody tests apparently failed to detect infected young birds. Questions have thus been raised about whether the traditional serological tests and antigens are still able to adequately detect infections with current field strains of S. pullorum. We evaluated the ability of standard agglutination test antigens, in both plate and tube assays, to detect infection in egg-type hens inoculated with large oral doses of six recent S. pullorum isolates. Using any of the antigens under consideration, antibodies to S. pullorum were found in the blood of most inoculated hens. The traditional antigens detected infections with recent S. pullorum strains as effectively as did antigens prepared from the recent strains. However, infections with some antigenic forms of S. pullorum were apparently more difficult to detect than others, regardless of the test or antigen used. Hens in which S. pullorum was found in the livers and ovaries were nearly always also positive in the antibody tests.
Technical Abstract: Despite extensive testing for Salmonella pullorum infections in commercial poultry, occasional outbreaks of pullorum disease still occur. In some recent instances, questions have been raised about whether standard serological assays, which employ antigen strains selected several decades ago, are still able to detect currently prevalent S. pullorum strains. The present study evaluated the ability of standard rapid whole-blood plate agglutination test and serum tube agglutination test antigens to detect infection in single-comb white leghorn hens inoculated with large oral doses of six recent S. pullorum isolates. Two commercially available plate test antigens were obtained and three tube test antigens were prepared. All five antigens identified most inoculated hens as seropositive, although some differences in sensitivity were evident between the two assay types and between the two plate test antigens. The antigenic composition of the tube test antigens did not affect their ability to detect infections with the various inoculum strains. Regardless of the antigen used, hens infected with antigenically intermediate or variant S. pullorum strains were detected as seropositive less often than were hens infected with antigenically standard strains. Positive culturing results for S. pullorum in the livers and ovaries of infected hens were nearly always predicted by positive serological tests.