Detecting infections of chickens with recent Salmonella pullorum isolates using standard serological methods

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 test results.