A longitudinal study of serological patterns of respiratory infections in nine infected Danish swine herds

Sixteen litters of seven pigs from each of nine Danish farrow-to-finish her ds were followed to investigate the serological patterns caused by natural infection with Mycoplasma hyponeumoniae, Pasteurella multocida toxin and Ac tinobacillus pleuroneumoniae serotypes 2, 5-7, 12. In seven of the herds, p igs were followed as two separate cohorts started 4 weeks apart, and in two herds only one cohort was followed. A total of 999 pigs were included in the study. The pigs were blood sampled at weaning and subsequently every fourth week until slaughter. All pigs we re examined for antibodies against M. hyopneumoniae (enzyme-linked immunoso rbent assay), P. multocida toxin (enzyme-linked immunosorbent assay) and A. pleuropneumoniae serotypes 2, 5-7, 12 (complement-fixation tests). The mos t-common pattern (28%) of seroconversion was that of pigs first seroconvert ing to A. pleuropneumoniae serotype 2, followed by seroconversion to M. hyo pneumoniae. Each herd had a dominant serotype of A. pleuropneumoniae to whi ch most pigs seroconverted. Seroconversion to the respiratory pathogens occ urred mainly in the growing-to-finishing units (8-24 weeks). The risk of se roconversion to the P. multocida toxin was very low (<20%) and occurred lat e. None, four and seven herds tested seropositive to PRRS and to swine influen za virus subtypes H3N2 and H1N1, respectively, when testing 10 pigs per her d (selected randomly among the study pigs) at the age of 20 weeks. (C) 2000 Elsevier Science B.V. All rights reserved.