A monoclonal antibody-blocking enzyme-linked immunosorbent assay for the detection of serovar-specific antibodies to Haemophilus paragallinarum

Two monoclonal antibody-blocking enzyme-linked immunosorbent assays (B-ELIS As) were developed to detect serovar-specific antibodies to Haemophilus par agallinarum. One assay detected antibodies against serovar A and the other antibodies against serovar C. The assays were evaluated with sera derived f rom disease-free chickens as well as chickens experimentally immunized and/ or challenged with H. paragallinarum strains 0083 (serovar A), Modesto (ser ovar C), or HP31 (serovar C). When rested with 440 negative sera (170 from a specific-pathogen-free and 30 from each of nine commercial layer flocks), both tests gave only a single false-positive reaction. The use of the B-EL ISAs with the experimentally produced sera showed the assays to be serovar specific. With the exception of one serum, the serovar A B-ELISA detected a ntibodies only in the chickens vaccinated with 0083. Similarly, with the ex ception of one serum, the serovar C B-ELISA detected antibodies only in cho se chickens vaccinated with Modesto or those chickens challenged with HP31. Overall, the serovar A B-ELISA had a specificity of 99.7% and a sensitivit y of 78.7%, whereas the serovar C B-ELISA had a specificity of 99.8% and a sensitivity of 64.7%.