Multifocal granulomatous hepatitis caused by Actinobacillus pleuropneumoniae serotype 2 in slaughter pigs

Examination of the Virulence of Actinobacillus pleuropneumoniae Serovar 16 in Pigs

Different virulence variants of A. pleuropneumoniae are involved in the etiology of porcine pleuropneumonia. The purpose of the present trial was examination of the virulence of the Actinobacillus pleuropneumoniae A-85/14 strain, the type strain of serovar 16, in an animal challenge experiment. Thirty 12-week-old piglets seronegative for A. pleuropneumoniae were allocated into three trial groups each of 10 animals, and they were infected intranasally with 106, 107, or 108 colony forming units (cfu) of the strain, respectively. Clinical signs were recorded twice a day, and the animals were euthanized 6 days after the infection. Typical clinical signs and postmortem lesions of porcine pleuropneumonia were seen in the animals of each trial group; however, they were generally mild, and no significant differences could be seen between the three groups. Even 106 colony forming units of A. pleuropneumoniae A-85/14 strain could induce clinical signs and lesions. Based on these results, the type strain of serovar 16 of A. pleuropneumoniae must be regarded as a typical pathogenic strain of the species.

[Alveolar echinococcosis in fattening pigs in a conventional housing system]

In a conventional fattening farm in southern Germany, up to 100 % of the livers of individual slaughter groups were condemned due to parasitic lesions during 2022. Intensification of antiparasitic metaphylaxis with fenbendazole to control Ascaris suum in the herd was unsuccessful. A pathomorphologic examination of 6 livers from two slaughter groups revealed oligofocal fibrotic inflammation. Histologically, chronic granulomatous hepatitis with massive involvement of eosinophilic granulocytes and central parasitic structures of a helminth were detected. Examination of the liver lesions by PCR revealed evidence of Echinococcus (E.) multilocularis. To determine the source of introduction into the herd, fecal samples were collected from semi-feral domestic cats near the feed mixer and in the corridor of the barn. Parasitologically, cestode eggs were detected in the fecal samples. Genome fragments of E. multilocularis could not be amplified by PCR. In the present case, domestic cats were suspected as the most likely source of entry into the herd. Control measures were aimed at preventing parasite entry by therapy of the domestic cats with antiparasitics. Differentially, no other possible pathogens could be detected by PCR and bacteriological examination.

Pulmonary lesions with asteroid bodies in a pig experimentally infected with Actinobacillus pleuropneumoniae serovar 15

Five pigs experimentally infected with Actinobacillus pleuropneumoniae serovar 15 isolated in our previous study were pathologically examined. One pig died at 2 days post inoculation (dpi) and four pigs were euthanized at 7 dpi. Autopsy revealed fibrinohemorrhagic pleuropneumonia in all pigs. Histopathologically, the lesions were characterized by extensive hemorrhage and necrosis, fibrin deposition, and multifocal abscesses composed of numerous neutrophils including oat cells and numerous Gram-negative bacilli. In one survived pig, asteroid body formation was confirmed in the lung. The bacteria within the abscesses and asteroid bodies were immunohistochemically positive for antiserum raised against A. pleuropneumoniae serovar 15. This is the first report describing porcine pleuropneumonia with asteroid bodies in a pig experimentally infected with A. pleuropneumoniae serovar 15.

Sero- and apx-typing of German Actinobacillus pleuropneumoniae field isolates from 2010 to 2019 reveals a predominance of serovar 2 with regular apx-profile

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.

Multi-organ spreading of Actinobacillus pleuropneumoniae serovar 7 in weaned pigs during the first week after experimental infection

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.

Prevalence of granulomatous pleuropneumonia associated with Actinobacillus pleuropneumoniae serotype 2 in slaughter pigs

A total of 14,818 slaughtered pigs were examined macroscopically. Of these, 25 pigs with porcine pleuropneumonia were collected and the relations among Actinobacillus spp. and granulomatous lesions in organs (lungs and tonsils) were evaluated. In the lungs, only Actinobacillus pleuropneumoniae serotype 2 was isolated from 20 of the pigs. Histologically, granulomatous pneumonia with A. pleuropneumoniae antigen was detected in 8 of the pigs. The antigen was visible in the centers of the lesions along with asteroid bodies, epithelioid cells and multinucleated giant cells. In the tonsils, granulomatous lesions were not detected, although A. pleuropneumoniae serotype 2 (5 pigs), serotype 7 (1 pig), Actinobacillus porcitonsillarum (1 pig) and Actinobacillus minor (1 pig) were isolated. The present survey suggests that multifocal granulomatous pneumonia in slaughter pigs could be highly associated with A. pleuropneumoniae serotype 2 infection.

In vivo induced RTX toxin ApxIVA is essential for the full virulence of Actinobacillus pleuropneumoniae

Actinobacillus pleuropneumoniae is a Gram-negative pathogen. It is the aetiological agent of porcine contagious pleuropneumonia (PCP), a severe and highly contagious and severe respiratory disease of swine. Four sets of RTX (repeats in toxin) exotoxins have been described in A. pleuropnuemoniae and three of them have been characterized as important virulence determinants. The aim of this study was to determine the pathogenicity of the invivo induced RTX toxin ApxIVA during infection of piglets with A. pleuropnuemoniae. An A. pleuropnuemoniae apxIVA mutant was obtained based on an A. pleuropnuemoniae apxIIC-deleted mutant strain. An experimental infection assay was performed to evaluate the virulence of ApxIVA in piglets. Clinical signs, lung lesion scores, blood biochemical parameters and histopathologic changes in the piglets were recorded. The results indicated that the pathogenicity of A. pleuropnuemoniae was greater when ApxIVA was present, suggesting that ApxIVA is essential for expression of the full virulence of A. pleuropnuemoniae.