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Title: Morphologic and phenotypic characteristics of myocarditis in two pigs infected by foot-and mouth disease virus strains of serotypes O or A

Author
item STENFELDT, CAROLINA - Oak Ridge Institute For Science And Education (ORISE)
item Pacheco Tobin, Juan
item Borca, Manuel
item Rodriguez, Luis
item Arzt, Jonathan

Submitted to: Acta Veterinaria Scandinavica
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/16/2014
Publication Date: 7/12/2014
Citation: Stenfeldt, C., Pacheco Tobin, J., Borca, M.V., Rodriguez, L.L., Arzt, J. 2014. Morphologic and phenotypic characteristics of myocarditis in two pigs infected by foot-and mouth disease virus strains of serotypes O or A. Acta Veterinaria Scandinavica. 56(1):42.

Interpretive Summary: Unexpected deaths that occur amongst animals infected with foot-and-mouth disease virus (FMDV) are often attributed to viral infection of the heart (myocarditis), but the underlying mechanism of this condition has never been described in detail. The current report describes two pigs that died during acute infection with either of two different strains of FMDV. We show for the first time that large quantities of FMDV were found in association with substantial injury and inflammation in heart muscle from both animals. Despite similar progression of the clinical infection, there were some differences in the extent of inflammation in the heart muscle of the two pigs suggesting a more advanced stage of disease in one of the two pigs. Identification of sub-populations of inflammatory cells showed that heart muscle from both pigs was invaded by similar populations of acute-phase cells. The cases are discussed in relation to other known viral infections of the heart.

Technical Abstract: Myocarditis is often cited as the cause of fatalities associated with foot-and-mouth disease virus (FMDV) infection; however the pathogenesis of FMDV-associated myocarditis has not been described in detail. The current report describes substantial quantities of FMDV in association with a marked mononuclear inflammatory reaction, interstitial edema and myocyte degeneration in the myocardium of two pigs that died during acute infection with either of two different strains of FMDV. Despite similar clinical progression, there was a marked variation in morphological characteristics of FMDV-associated myocarditis with a significant difference in intensity of myocardial inflammation between the two cases. Phenotypic characterization of leukocyte populations revealed that in both cases, the inflammatory infiltrate consisted mainly of combinations of CD172a positive, CD163 positive and CD44 positive cells, with a distinct subset of CD8 positive cells, but with consistent lack of detection of CD3 positive and CD21 positive cells. This suggests that the FMDV associated acute myocardial inflammation in the two observed cases consisted mainly of infiltrating cells of monocyte lineage, with a distinct population of CD8 positive cells which, based on lack of concurrent CD3 detection, are likely to represent NK cells.