Abstract
Serotyping is the most common method to characterize field isolates of Actinobacillus (A.) pleuropneumoniae, the etiological agent of porcine pleuropneumonia. Based on serology, many farms seem to be infected and antibodies against a wide variety of serovars are detectable, but, so far it is unknown to what degree respective serovars contribute to outbreaks of clinical manifest disease. In this study, 213 German A. pleuropneumoniae field isolates retrieved for diagnostic purposes from outbreaks of porcine pleuropneumonia between 2010 and 2019 were genetically serotyped and analyzed regarding their apx-toxin gene profile using molecular methods. Serotyping revealed a prominent role of serovar 2 in clinical cases (64% of all isolates) and an increase in the detection of this serovar since 2010 in German isolates. Serovar 9/11 followed as the second most frequent serovar with about 15% of the isolates. Furthermore, very recently described serovars 16 (n = 2) and 18 (n = 8) were detected. Most isolates (93.4%) showed apx-profiles typical for the respective serovar. However, this does not hold true for isolates of serovar 18, as 75% (n = 6) of all isolates of this serovar deviated uniformly from the “typical” apx-gene profile of the reference strain 7311555. Notably, isolates from systemic lesions such as joints or meninges did not harbor the complete apxICABD operon which is considered typical for highly virulent strains. Furthermore, the extremely low occurrence (n = 1) of NAD independent (biovar II) isolates in German A. pleuropneumoniae was evident in our collection of clinical isolates.
Highlights
The etiological agent of porcine pleuropneumonia, A. pleuropneumoniae, is a bacterial pathogen belonging to the family of Pasteurellaceae, affecting pigs worldwide [1]
Serovar 2 was described as the dominating serovar in Hungary, Belgium and, among others, in Denmark and the Netherlands [23,24,25], while the important role of serovar 8 in Great Britain and serovar 7 in Spain was demonstrated [26, 27]
Our results support a dominance of serovar 2 in central European regions and highlight geographical differences within Europe as compared to the Iberian Peninsula or Great Britain as well as across other continents. This highlights the need for serotyping in order to select appropriate vaccines for porcine pleuropneumonia in different countries or regions as long as no efficient serotype-independent vaccine strategies are available
Summary
The etiological agent of porcine pleuropneumonia, A. pleuropneumoniae, is a bacterial pathogen belonging to the family of Pasteurellaceae, affecting pigs worldwide [1]. The bacterium is contributing to porcine respiratory disease complex (PRDC), one of the most important economic challenges in pig farming [2]. Infections with A. pleuropneumoniae are well known to be associated with lesions of porcine pleuropneumonia (fibrino-hemorrhagic pleuropneumonia). Systemic spreading of the pathogen in the host with associated lesions (e.g. arthritis, meningitis) is reported and thought to be due to hematogenic and/or lymphogenic dissemination [3,4,5]. The bacterium is characterized by the occurrence of numerous serovars, which can be distinguished by the expression of different capsular antigens and which are associated with different courses of disease [7]. Serovar-based pathogen typing is the most important
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