Mycoplasma hyopneumoniae - an unusual cause of fibrinous pericarditis with pericardial tamponade in pre-weaned piglets.

M. hyopneumoniae is an atypical bacterium that is frequently associated with porcine enzootic pneumonia, but uncommonly identified as a cause of pericarditis and myocarditis leading to pericardial tamponade. The present report describes the rare case of M. hyopneumoniae causing fibrinous pericarditis and pericardial tamponade in pre-weaned crossbred piglets (n = 7). The piglets showed the predominant lesions of pericardial effusions with tamponade, fibrinous pericarditis, pleural effusions, heavy non-collapsible lungs with multifocal reddish areas on parenchyma, and enlarged lymph nodes. Microscopically, sub-acute fibrinous pericarditis, pleuritis, brocho-interstitial pneumonia with lymphoid depletion in the lymphoid organs were the consistent lesions observed in the piglets. The piglets showed the strong immunoreactivity to M. hyopneumoniae antigens in the infiltrating mononuclear cells, cardiomyocytes, and purkinje fibers of heart, bronchioles, and alveolar lining epithelium of lungs, and lymphocytes of the depleted lymphoid follicles of the lymph nodes. The absence of immunoreactivity to M. hyorhinis in the heart ruled out the cross specificity and confirmed the involvement of M. hyopneumoniae with the cardiac pathologies. Further, M. hyopneumoniae was confirmed in heart, pericardium, and lungs of the piglets by PCR suggesting the role of M. hyopneumoniae with the cardiac lesions. The absence of any other possible etiologies (bacteria/and virus) in the heart tissues further confirms M. hyopneumoniae as a cause of cardiac lesions. Among various viruses screened, lungs, lymph nodes, and liver of the piglets showed the genomic detection of porcine circovirus 2 along with strong cytoplasmic immunolabeling of viral antigens in lungs and lymph nodes. This indicates that co-infection of M. hyopneumoniae and porcine circovirus 2 might be playing a synergistic role by potentiating each other in causing severe pathologies involving lungs and heart. This paper highlights that M. hyopneumoniae should be considered in the differential diagnosis of pneumonia complicated by pericardial effusion leading to complication of pericardial tamponade and should be part of the routine workup for pericarditis of unknown etiology for the effective control and management of piglet mortality. Moreover, the presence of immunosuppressive disease like porcine circovirus 2 has also to be considered as the predisposing factor for the development of fibrinous pericarditis.