Serological patterns of Actinobacillus pleuropneumoniae, Mycoplasma hyopneumoniae, Pasteurella multocida and Streptococcus suis in pig herds affected by pleuritis

Wallgren, Per; Nörregård, Erik; Molander, Benedicta; Persson, Maria; Ehlorsson, Carl-Johan

The serological pattern in herd D suggested a minor impact of A. pleuropneumoniae despite the high frequencies of pleuritic lesions recorded at slaughter. The mean concentration of antibodies to A. pleuropneumoniae serotype 2 and 3 remained below the cut offvalue during the entire rearing period. Instead, pigs were seropositive to P. multocida already on arrival to the fattening unit and the level of serum antibodies to P. multocida increased throughout the rearing period in absence of antibodies to the other microbes. This clearly indicated that pleuritic lesions may evolve at high frequencies also in absence of A. pleuropneumoniae, as also has been suggested by others [33] . Likewise, no correlation between A. pleuropneumoniae and pleuritis at individual level was seen in herds with low incidences of pleuritic lesions recorded at slaughter [34] . Instead seroconversion to M. hyopneumoniae during the early fattening period was related to pleuritis at an individual level in such herds, which indicated an influence of secondary infections [34] . Therefore, the common presence of serum antibodies to P. multocida is of interest. However, in the present study, P. multocida was associated with a high prevalence of pleuritic lesions recorded at slaughter in absence of M. hyopneumoniae. Thereby, the true initial cause for these lesions still remains unknown and warrants further investigations. Since viral infections repeatedly has been demonstrated during the early fattening period [15, 16] viral infections may well have preceded the serological response to P. multocida.