Prevalence of Actinobacillus pleuropneumoniae serotypes in swine in Germany

Actinobacillus pleuropneumoniae (App) is the etiological agent of pleuropneumonia in pigs. Although an old bacterial pulmonary pathogen, it is still relevant in the 21st century and occurs worldwide. At present, 15 serotypes have been differentiated by antisera. The distribution of serotypes involved in clinical cases in different regions varies drastically. Moreover, strains of a certain serotype may typically be highly virulent in one region while strains of the same serotype may typically be of low virulence in another. Because the available data were not current, we analyzed serotyping results of App strains isolated from swine in Germany within the last four years.

A total of 565 App isolated from swine during diagnostic examinations between 2012 and 2015 were analyzed for their serotype by multiplex PCR testing based on apx and cps genes. The distribution of serotypes of App were analyzed for the total population in comparison to two subpopulations of strains, i) those isolated from swine with respiratory symptoms (n = 197) and ii) those definitely isolated from the porcine lung (n = 140); and for annual variations.

Serotype 2 is the predominant App isolated in the total population (66.4%) and in both subpopulations i) (71.6%) and ii) (61.6%). The next most prevalent App serogroup comprised serotypes 1, 9, and 11: 13.1% in the total population, 10.2% in subpopulation i), and 15.0% in subpopulation ii). The prevalences of serotypes 5 and 6 were lower, between 5.0% and 6.5% in all populations. The prevalence of serotype 7 was slightly higher, at 7.9% in subpopulation ii), where App was isolated only from porcine lungs, but it was less prevalent in the total population (2.7%) and in subpopulation i) swine with respiratory symptoms (2.5%). While the prevalence of App serotype 2 varied from year to year between 82 and 110 (6.3%> 7.0%), there was a low-level increase in App serogroup 1/9/11 over the years (2012: 10 (7.6%); 2013: 14 (10.9%); 2014: 22(14.0%); 2015: 28 (18.7%)).

Although past and present methods for serotyping are totally different, App 2 remains the most predominant serotype in Germany associated with clinical respiratory symptoms and definitely isolated from the porcine lung. The considerable level of App recorded in German pig stocks confirms the need for constant monitoring of prevalence and serotypes, especially with respect to its central role in lung health and animal welfare. In conjunction with other bacterial and viral pathogens like Porcine Reproductive and Respiratory Syndrome virus App seems to be a key factor in the pulmonary health of affected pigs.

Disclosure of Interest: None Declared.