Abstract
Actinobacillus (A.) pleuropneumoniae is normally considered strictly adapted to the respiratory tract of swine. Despite this, scattered case reports of arthritis, osteomyelitis, hepatitis, meningitis or nephritis exist, in which A. pleuropneumoniae remained the only detectable pathogen. Therefore, the aim of this study was to investigate whether spreading to other organs than the lungs is incidental or may occur more frequently. For this, organ samples (blood, liver, spleen, kidney, tarsal and carpal joints, meninges, pleural and pericardial fluids) from weaners (n = 47) infected experimentally with A. pleuropneumoniae serovar 7 by aerosol infection (infection dose: 10.9 × 103 cfu/animal) were examined by culture during the first week after infection. In addition, tissue samples of eight weaners were examined by histology and immunohistochemistry (IHC). A. pleuropneumoniae was isolated in all examined sample sites (86.7% pleural fluids, 73.3% pericardial fluids, 50.0% blood, 61.7% liver, 51.1% spleen, 55.3% kidney, 14.9% tarsal joints, 12.8% carpal joints, 27.7% meninges). These results were also obtained from animals with only mild clinical symptoms. IHC detection confirmed these findings in all locations except carpal joints. Histological examination revealed purulent hepatitis (n = 2), nephritis (n = 1) and beginning meningitis (n = 2). Isolation results were significantly correlated (p < 0.001) with the degree of lung colonization and, to a lower extent, with the severity of disease. Detection of A. pleuropneumoniae in peripheral tissues was significantly correlated to spleen colonization. In conclusion, multi-organ spreading of A. pleuropneumoniae serovar 7 strain AP 76 seems to occur more frequently during acute infection following effective lung colonization than previously thought.
Highlights
Actinobacillus (A.) pleuropneumoniae, a Gram-negative bacterium belonging to the family Pasteurellaceae, is one of the most important respiratory tract pathogens in the pig industry
The detection of A. pleuropneumoniae in pleural und pericardial fluids of pigs during acute infection are in accordance with earlier studies on porcine pleuropneumonia pathogenesis describing the mechanism of spreading of the pathogen within the pleural cavity via lymph vessels and by oedematous fluids [13] and describing the incidence of viable bacteria in pericardial fluids in cases of severe pleuropneumonia [27]
Though there was a significant correlation between the degree of clinical disease and lung lesions and detected cfu within the pericardial fluids, we could show, that, in contrast to Nicolet and König [27], A. pleuropneumoniae does appear in the pericardial fluids of animals developing a severe disease after infection, and in the pericardial fluids of pigs only showing mild clinical symptoms and mild lung lesions
Summary
Actinobacillus (A.) pleuropneumoniae, a Gram-negative bacterium belonging to the family Pasteurellaceae, is one of the most important respiratory tract pathogens in the pig industry. Despite its non-invasive character there are several case reports about non-respiratory clinical diseases in which A. pleuropneumoniae was the only detectable pathogen These reports include cases of fibrino-purulent arthritis and necrotizing osteomyelitis [14], granulomatous hepatitis [15], meningitis and, nephritis [16] as well as endocarditis and fibrinous peritonitis [17]. These recurring case reports prompted us to find out if A. pleuropneumoniae can be detected more frequently within different body tissues during the acute phase of disease. We investigated possible spreading of A. pleuropneumoniae to body tissues other than the lungs in experimentally infected weaners
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