Anatomopathological pneumonic aspects associated with highly pathogenic Pasteurella multocida in finishing pigs

Abstract

The bacterium Pasteurella multocida is a frequent cause of porcine respiratory disease complex in finishing pigs. Historically, the bacterium is recognized as an opportunistic agent, causing secondary bacterial pneumonia in pigs. Several Brazilian reports have suggested the ability of P. multocida to cause primary pulmonary infection that leads to the death of finishing pigs prior to slaughter. The aim of this study was to evaluate anatomopathological pulmonary findings associated with P. multocida infection that were obtained from animals with clinical respiratory disease and from animals at slaughter. Twenty-five lung samples from 14 herds of finishing pigs with acute clinical respiratory disease and 19 lungs collected at slaughter from a different set of 14 herds were studied. In all lung samples, bacterial isolation was performed, and only samples with pure P. multocida growth were included in the study. Gross and histopathological lesions were evaluated, as well as Influenza A, porcine circovirus type 2 (PCV2) and Mycoplasma hyopneumoniae co-infections. Pleuritis and pericarditis were more often observed in clinical samples (P<0.05). Moreover, there was a numerical trend indicating that pericarditis, lymphadenomegaly and cavity exudates were more often present in clinical samples. Thirteen lung samples were negative to M. hyopneumoniae, Influenza A and PCV2 by immunohistochemistry (IHC), with only P. multocida identified. In these cases, gross lesions such as pleuritis, pericarditis and lymphadenomegaly were always present, and no histologic lesions indicative of other agents such as Actinobacillus pleuropneumoniae, Actinobacillus suis or Haemophilus parasuis were observed. These findings suggest the ability of some P. multocida isolates to cause primary respiratory and systemic infection. However, in this study, it was not possible to determine specific virulence markers to explain these findings.

Agents of pneumonia in slaughtered pigs in southern Brazil

“…Morés et al (2015) have detected 100% of P. multocida type A from pig lungs with P. multocida isolation. Although this serotype has been described as a primary role in the induction of lesions in the respiratory tract (Paladino et al 2017, Oliveira Filho et al 2018, in this study we did not observe lesions suggestive of P. multocida highly pathogenic strain. The frequent isolation of P. multocida type A (43.3%; 65/150) in our study is probably related to the correlation between Mycoplasma hyopneumoniae and P. multocida type A infections (Takeuti et al 2013), as we found an average prevalence, in all lungs, of 79.3% of M. hyopneumoniae positive samples by qPCR, reaching 100% of the lungs from company D. The pathogenic mechanisms of this correlation are suggested to be due to the L-fucose composition increased by M. hyopneumoniae and thereby enhancing the adherence of P. multocida type A to the bronchial and bronchiolar epithelial cells (Park et al 2016).…”

“…The isolation of this bacterium was expected since it is reported to be more prevalent than other P. multocida serotypes in lung coinfections. In a recent study, 90.9% of the P. multocida isolated in pigs lungs were type A and only 9.1% type D (Paladino et al 2017). Morés et al (2015) have detected 100% of P. multocida type A from pig lungs with P. multocida isolation.…”

Causes of death in growing-finishing pigs in two technified farms in southern Brazil

“…As already addressed, highly pathogenic strains of P. multocida have potential to produce primary lesions of necrohemorrhagic pneumonia, pleuritis, and fibrinous pericarditis (Cappuccio et al 2004. In the present study, polyserositis lesions with isolation of P. multocida were observed in 17 cases (62.9% of polyserositis), sometimes also associated with pneumonia (Paladino et al 2017, Oliveira Filho et al, 2018. Thus, it is suggested that strains of high pathogenicity of P. multocida may be circulating in Brazilian herds, causing mortality and possibly chronic injuries, which can lead to condemnations in slaughterhouses.…”

“…Previously, P. multocida was highlighted as a secondary and opportunistic bacterium of the respiratory tract of pigs, mainly related to co-infection with M. hyopneumoniae (Pijoan & Fuentes 1987, Hansen et al 2010. Currently, P. multocida has been also associated with primary lesions of pneumonia and septicemia in pigs (Cappuccio et al 2004, Kich et al 2007, Pors et al 2011, Paladino et al 2017, and it is known to produce suppurative, necrosuppurative and necrohemorrhagic bronchopneumonias, as well as pleurites, especially when there is the involvement of strains of high pathogenicity (Paladino et al 2017, Oliveira Filho et al 2018. In this study, bacterial isolation was possible in 61.30% of bacterial pneumonia cases.…”

Review on the methodology to assess respiratory tract lesions in pigs and their production impact

“…This is the case in intensive production systems, where large groups of pigs are housed in confinement [ 2 ]. The two most prevalent pulmonary conditions observed in pigs on abattoir inspection are suppurative bronchopneumonia, characterized by cranioventral pulmonary consolidation (CVPC), and pleuritis or pleurisy, which is most frequently seen over the caudal lobes [ 1 , 3 – 5 ]. As these lesions are rather easy to examine at the slaughter line, they are often assessed in epidemiological studies and/or monitoring systems [ 1 , 6 ].…”