EVALUATION OF PIG LUNGS FOLLOWING AN EXPERIMENTAL CHALLENGE WITH ACTINOBACILLUS-PLEUROPNEUMONIAE SEROTYPE-1 AND SEROTYPE-5 IN PIGS INOCULATED WITH EITHER HEMOLYSIN PROTEIN AND OR OUTER-MEMBRANE PROTEINS/

Histopathological changes were compared in pigs challenged with Actino bacillus pleuropneumoniae serotype 1 and serotype 5 after inoculation with subunit vaccines. The vaccines consisted of outer membrane protei n and/or hemolysin protein isolated from Actinobacillus pleuropneumoni ae serotype 1 or both subunits combined. Twenty-seven cross-bred pigs were separated into six groups: Groups I and IV were vaccinated and bo ostered with 1500 mu g outer membrane protein; Groups II and V were va ccinated and boostered with 250 mu g hemolysin protein; Groups III and VI were vaccinated and boostered with a combination of 1500 mu g oute r membrane protein and 250 mu g hemolysin protein. Groups I, II and II I were challenged with A. pleuropneumoniae serotype 1; and Groups IV, V and VI were challenged with A. pleuropneumoniae serotype 5. Groups I II and VI demonstrated the least severe lung tissue damage, with signi ficantly lower (P < 0.05) lung involvement as compared to the other gr oups. Lesions were noted in all six groups. These results showed that complete protection against A. pleuropneumoniae infection was not feas ible using a subunit vaccine consisting of just outer membrane protein and hemolysin protein, and that some cross-protection did occur.