Transmission and immune response studies of toxigenic Pasteurella multocida
Lawrence E. Evans
Progressive atrophic rhinitis is an upper respiratory disease in swine thought to decrease average daily gain and feed efficiency. It is caused by toxigenic Pasteurella multocida colonizing the nasal or oropharyngeal cavities;The use of beta-hydroxy beta-methyl butyrate (HMB) as an adjunct to vaccination was investigated. Gilts vaccinated with a commercially available killed pseudorabies (PRV) vaccine, a P. multocida bacterin/toxoid and a tetanus toxoid received 0, 2 or 10 gm HMB top-dressed on the feed once daily;Serum and nasal secretion samples were assayed by ELISA to find serum and nasal class specific antibody titer. The anti-tetanus and anti-PRV titers in those pigs fed two grams of HMB per day tended to be higher than those of the other two HMB treatment groups. There were no statistical differences in nasal anti-PMT IgA or anti-PMT IgG among the HMB treatment groups;Class specific antibody titers in serum and on the nasal mucosa were measured in feeder pigs following experimental infection and/or vaccination with toxigenic P. multocida. Serum anti-PMT IgA was not a sensitive indicator of infection or vaccination, while nasal anti-PMT IgA demonstrated transmission. Culture and nasal antibody titer implied a protective effect of vaccination. Transmission was shown by culture as early as seven days and by serum anti-PMT IgG titers within 21 days post-experimental exposure;To study the reliability of bacterial isolation, restriction endonuclease analysis (REA), serotyping and toxigenicity were used on cultures of toxigenic Pasteurella multocida recovered from feeder pigs. Isolates from nasal swab cultures demonstrated P. multocida transmission from the exposed to nonexposed pigs, confirmed by REA, serotyping and P. multocida toxin ELISA. Co-existent nontoxigenic P. multocida strains of the same somatic type but easily differentiated from P4148 by REA and toxigenicity were recovered;Antibody assay of secretions directly from the mucosal surface helped evaluate vaccination and immune system enhancers. Better defining transmission detection methods is central to accurately describing the epidemiology of toxigenic P. multocida and developing disease intervention strategies.