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

When Sweden in 1986 as the first country in the world banned the use of low dose antibiotics in animal feed for growth promotion, some introductory health disturbances were recorded. As a consequence, a strict age segregated rearing from birth to slaughter was implemented in a large scale, which improved health as well as productivity [19, 20] . As seen in Fig. 1 , the incidence of recorded pathogenic lesions in the respiratory tract at slaughter decreased during the last decade of the twentieth century [21] . The registrations of pneumonia at slaughter has remained stable at that level since then. In contrast, the incidence of recorded pleuritis at slaughter has continuously increased since the year 2000, as has the clinical evidence of actinobacillosis [22] . Discussions concerning the reason for this increase has included suggestions of introduction of new strains, or mutation of existing strains of A. pleuropneumoniae. However, acute actinobacillosis has in Sweden historically been dominated by serotype 2, and is still dominated by that serotype [22] . Further, Pulse Field Gel Electrophoreses has revealed that strains isolated in the twenty-first century were identical to strains isolated in the 1970s and 1980s [23] . As a consequence, the increase of actinobacillosis and pleuritic recordings at slaughter has merely been linked to the continuously increasing herd sizes with increasing number of transmissions of microbes between pigs, within and between units [22] .