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

In herd C the serological response to P. multocida was strong (A 450 > 1.5) and preceded that to A. pleuropneumoniae serotype 2, and the influence of P. multocida therefore should be regarded as even more significant in this herd. Still, the increasing levels of antibodies to A. pleuropneumoniae serotype 2 at the end of the rearing period suggested an influence of A. pleuropneumoniae also in this herd, and it is notable that the levels of antibodies to M. hyopneumoniae increased slightly during the end of the rearing period. As P. multocida is regarded to be a secondary invader, something else than A. pleuropneumoniae or M. hyopneumoniae ought to have paved the way for that microbe. Although this remain undiagnosed in the present study, the frequent demonstrations of interferon-α in serum of fattening pigs during the first week after allocation [15, 16] indicate that viral infections may be precursors to P. multocida and the frequent findings of different virus in pigs using novel techniques [32] support that hypothesis. The early infections with P. multocida may by themselves not necessarily have induced pleuritic lesions, but obviously the infection with P. multocida already was established as the pigs became infected with A. pleuropneumoniae and colonies of P. multocida already on site may have amplified the effect of the subsequent A. pleuropneumoniae infection.