Serological response to Actinobacillus pleuropneumoniae serovar 7 infection in a commercial pig herd

Serological responses to A. pleuropneumoniae serovar 7 infection were monitored by ELISA in a cohort of 66 pigs between weaning and market. Antibody concentrations were high (63/65 seropositive) at 4 weeks of age but declined to low levels from 8 to 12 weeks. Mean antibody concn rose significantly between 12 and 23 weeks. Between 8 and 23 weeks of age, 33 (51.5%) of 64 surviving pigs seroconverted to A. pleuropneumoniae serovar 7. Peak antibody concentrations in the seroconverting pigs usually (28/33) occurred at 23 weeks. Seroconversion to A. pleuropneumoniae during the grower/finisher phase was not significantly associated with passive antibody concn at 4 weeks of age, lack of vaccination against Mycoplasma hyopneumoniae, or weaning weight. Pleuropneumonic lesions were evident at slaughter in 4 (6.3%) of 64 pigs. A. pleuropneumoniae serovar 7 was isolated from 2 of 4 lungs with pleuropneumonia and from another lung with lesions considered typical of enzootic pneumonia.