Protection of mice and swine against infection with Actinobacillus pleuropneumoniae by vaccination.

CaCl2 and LiCl cell extracts and a crude hemolysin preparation were isolated from Actinobacillus pleuropneumoniae serotype 1 strain 4074 and tested for protection against A. pleuropneumoniae serotype 1 and 5 in mice. The LiCl cell extract adsorbed on AlPO4 and the crude hemolysin preparation adsorbed on Al(OH)3 showed a highly significant protection (P < 0.01) against both serotypes. Different vaccine preparations were used to immunize pigs by intra-muscular injection at days 0 and 14; the pigs were then challenged at day 21 by intra-tracheal inoculation of 1 x 10(8) colony forming units (CFU) of a serotype 1 strain 4074. A vaccine which combined the LiCl extract and the crude hemolysin preparation adsorbed on Al(OH)3 gave the best protection with no mortality and no sign of morbidity in the vaccinated pigs. In the other experimental groups which included a group immunized with a commercial bacterin, mortality, respiratory disease and extensive pulmonary lesions were noted. This mixture shows good potential as a vaccine against pleuropneumonia in pigs.