EVALUATION OF LONG-CHAIN LIPOPOLYSACCHARIDES (LC-LPS) OF ACTINOBACILLUS-PLEUROPNEUMONIAE SEROTYPE-5 FOR THE SERODIAGNOSIS OF SWINE PLEUROPNEUMONIA

Long chain lipopolysaccharides (LC-LPS) of Aetinobaeillus pleuropneumo niae serotype 5 have been evaluated and compared with a crude boiled e xtract (CBE) in ELISA for the serodiagnosis of swine pleuropneumonia c aused by this serotype. The mean optical density (OD) obtained with th e LC-LPS in ELISA using sera from negative herds as well as from anima ls experimentally and naturally exposed to A. pleuropneumoniae serotyp e 5 was not significantly different from that obtained with the CBE. H owever, sera from animals exposed to serotypes of A. pleuropneumoniae other than serotype 5 presented a significantly lower mean OD (P<0.05) when the LC-LPS was used. As a consequence, it was demonstrated that a high percentage of non-specific cross-reactions were eliminated, wit hout losing specificity. The specificity and the sensitivity of the LC -LPS- and CBE-ELISA were evaluated using two different cut-off values (the OD plus two and three standard deviations) (SD) obtained from 593 sera from negative herds. The LC-LPS appeared a more suitable antigen than the CBE, since the sensitivity and the specificity (obtained wit h both thresholds) were statistically improved (P<0.01). A threshold o f 0.244 (mean OD plus three SD) for the LC-LPS-ELISA seemed more suita ble, since a sensitivity of 79% and a specificity of 97% was achieved. Nevertheless, it may be advisable to keep a buffer range (OD between 0.194 and 0.243) and to consider sera presenting values within this ra nge as suspicious. In the present study, the complement fixation test presented a high specificity (97%) and a very low sensitivity (47%). A herd with animals presenting ELISA positive and CFT negative results in serology, along with the absence of suggestive lesions should not b e considered as a non-infected herd.