Reemerging of Encephalomyocarditis Virus in Pigs in Brazil: Pathological and Viral Characterization

Abstract

Encephalomyocarditis virus (EMCV) is a zoonotic disease caused by a highly pathogenic virus that affects wild and domestic animal species, with rodents as its reservoir. Most recently, in South America, this virus was detected in an outbreak affecting humans in Peru. In Brazil, EMCV infection was described in some wild species, in horses, and once in farrowing pigs. The aim of this study is to report the reemergence of EMCV in commercial growing-finishing pigs from two different farms that experienced sudden pig death in midwest Brazil. This aim was achieved through gross pathology, histologic examination, RT‒PCR analysis, and genetic characterization of the virus. Clinical signs, such as trembling, dyspnea, and squealing sounds shortly before death, were only occasionally observed and were nonspecific. On gross examination, cardiomegaly was observed, along with multifocal pale tan foci in the epicardium extending to the myocardium on the cut surface. Microscopically, there was severe myocardial necrosis, dystrophic mineralization, fibrosis, and lymphoplasmacytic and histiocytic myocarditis. Gross and microscopic examinations of the rats were unremarkable. The RT‒PCR analyses of the pig and rat organs were positive for EMCV, and the phylogenetic analysis of the VP1 gene showed that the samples from pigs and rats contained similar strains that had their closest relatives identified in humans in Peru. This is the first genetic characterization of EMCV in Brazil, and the other findings confirm the reemergence of the disease that was transmitted from rats to pigs.

Figure 1

Gross lesions of pigs naturally infected by EMCV. (a) Heart: the surface of the epicardium and myocardium presents multifocal to coalescent areas of 0.5–1 cm in diameter or in a linear pattern with a pale tan discoloration on both sides of the ventricle. Pig 2, Farm B. (b) Heart cross-section: nearly 80% of the myocardium of both atria, ventricles, and interventricular septa have multifocal to coalescent pale tan discoloration foci measuring 0.3–1 cm in diameter with occasional opaque white areas (arrow) measuring up to 0.5 cm in diameter. Microscopically, the latter corresponds to dystrophic mineralization. Pig 3, Farm B.

Figure 2

Microscopic findings of the myocardium of pigs naturally infected by EMCV. (a) Myocardium showing severe multifocal to coalescent inflammation associated with proliferation of fibrous connective tissue (fibrosis) and some areas of intense basophilic material (mineralization) are observed. Pig 2, Farm B, hematoxylin and eosin (HE), 200x. (b) Higher magnification of the myocardium demonstrating the inflammatory infiltrate of lymphocytes, plasma cells, and macrophages with fibrosis and mineralization. Pig 2, Farm B, HE, 400x.

Figure 3

Nucleotide tree constructed using sequences of the VP1 gene. Phylogenetic reconstruction based on VP1 sequences of EMCV. The phylogenetic tree was constructed with the MEGA 6 software using the maximum likelihood algorithm method based on the HKY + G model in 1,000 replicates. The letters at the right extremity represent the species of the genus Cardiovirus. The sequences obtained in the present study aligned within the species Cardiovirus A and were deposited in the GenBank database under accession numbers OR553571 and OR553570.