Dealing with unexpected Actinobacillus pleuropneumoniae serological results

Serological testing is widely used to monitor swine herds for Actinobacillus pleuropneumoniae (APP). Several serological tests are presently used, most often the complement fixation test, the long-chain lipopolysaccharide enzyme-linked immunosorbent assay (ELISA), and the ApxIV ELISA. Serological testing occasionally generates ambiguous results. In such situations, bacterial isolation and polymerase chain reaction testing must be used in order to accurately define the presence or absence of APP. Examples of unexpected serological results and the eventual means of establishing herd APP status are illustrated by means of 10 cases that occurred in European and North American herds.