Relationship between the amounts of antibodies to Actinobacillus pleuropneumoniae serotype 2 detected in blood serum and in fluids collected from muscles of pigs

An indirect ELISA method, previously used to detect antibodies to Actinobac illus pleuropneumoniae serotype 2 in serum of pigs, was further developed a iming to measure antibodies to the microbe in muscle fluids. Serum and musc le fluid were collected from Specific Pathogen Free (SPF) pigs as well as f rom SPF pigs challenged with A. pleuropneumoniae which were either treated with effective antibiotics or left as infected controls. The antibody respo nses measured in serum correlated well to the clinical signs of respiratory disease observed and to pathological lesions found at necropsy performed 1 7 days postinfection. The amounts of antibodies monitored in serum and in m uscle fluid collected from the diaphragm and the thigh, respectively, were compared. Higher concentrations of antibodies were assessed in serum than i n diaphragm fluid, which in turn contained more antibodies per mi than flui d collected from the thigh. The amount of antibodies to A. pleuropneumoniae measured in fluid from the diaphragm diluted 1/50 correlated well with the quantity measured in serum diluted 1/1000 (r(2) = 0.87; P < 0.001). When v alidated by using serum antibody responses as a standard, the specificity o f the ELISA employed in fluid from the diaphragm was found to be 100%. The sensitivity was determined to be 88% when calculated on seropositive pigs ( A(450) = 0.3 in serum diluted 1/1000). That figure increased to 97% if calc ulated on pigs expressing pronounced amounts of serum antibodies (A(450) <g reater than or equal to> 0.5).