Persistence of viral genome into late stages of murine myocarditis detected by polymerase chain reaction.

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Abstract
BACKGROUND Enteroviruses have been considered as the most common etiologic agents in clinical myocarditis and dilated cardiomyopathy; however, their pathogenetic role remains unknown. Hence, the relation of viral replication and development of cardiomyopathy has been determined in a murine model of myocarditis by evaluating the persistence of viral genome during acute and chronic stages of myocarditis by means of Northern blot hybridization and polymerase chain reaction (PCR). METHODS AND RESULTS DBA/2 mice (n = 146) were injected peritoneally with 10 plaque-forming units of encephalomyocarditis (EMC) virus, and the control mice (n = 33) were injected with normal saline. Animals were randomly killed at 4, 7, 10, 14, 21, 28, 35, and 42 days after infection. Histology revealed acute myocardial necrosis with massive inflammatory cell infiltrate peaking on day 14 followed by increasing fibrosis and declining chronic inflammation features compatible with dilated cardiomyopathy between days 21 and 42. Northern blot analysis of control and infected hearts showed detectable viral RNA in the infected hearts initially at day 4, peaking by day 7, diminishing between day 7 and day 14, and absent at day 21 and day 28. However, potential viral remnants present in low quantities and undetectable by Northern blot were further detected by PCR followed by confirmation with an internal oligonucleotide probe after day 14 up to day 42. CONCLUSIONS Viral RNA signals on Northern blot showed a strong correlation with massive myocyte necrosis on day 14, but the viral RNA fragment was consistently detectable into late stages of cardiomyopathy on days 21, 28, 35, and 42 by PCR. This indicated that the mature virions are fully developed early in infection and are capable of persisting in the myocardium after virus-mediated myocytolysis stage. Therefore, PCR is an extremely sensitive method for detecting residual viral genome and viral persistence in the myocardium and may offer insights into the pathogenesis of chronic myocarditis leading to dilated cardiomyopathy.