COMPARISON OF SERUM RESPONSES IN SWINE AFTER VACCINATION AND CHALLENGE EXPOSURE WITH ACTINOBACILLUS-PLEUROPNEUMONIAE SEROTYPE-1

Clinical trials have shown that currently available commercial vaccine s against porcine pleuropneumonia provide inconsistent, serotype-speci fic protection from the disease. Recovery from naturally acquired infe ction, however, provides solid, serotype cross-protective immunity. We examined various serum responses of pig receiving 1 of 4 commercial v accines or a cell extract, and compared the serologic responses of the se pigs after challenge exposure with virulent Actinobacillus pleuropn eumoniae serotype 1. Evaluation of serum included complement-mediated killing, opsonizing capacity, IgG titers to whole organisms, and cytot oxin neutralization titers. Pigs that received the cell extract had fe wer clinical signs of pleuropneumonia than pigs in other vaccinated gr oups, and also were significantly (P < 0.05) better protected from dev elopment of lung lesions and death. Such vaccinates were the only pigs that developed significant (P < 0.05) serum antibody titers (ie, prot ective immune response) to whole-cell antigens and to cytotoxin.