Experimental myocarditis induced by two different coxsackievirus B3 variants: aspects of pathogenesis and comparison of diagnostic methods.

The ability of two coxsackievirus B3 (CBV3) variants to induce myocarditis in BALB/c mice was studied and plaque-forming assay, polymerase chain reaction (PCR), in situ hybridization, and immunohistochemistry were compared for detecting viruses and viral components in the myocardium. The virological findings were related to histopathologic and ultrastructural changes in the myocardium. CBV3-W induced severe myocarditis characterized by massive myocyte necrosis. Widely distributed myocyte damage clearly preceded modest inflammatory infiltrates in the myocardium. In contrast, CBV3-M1 induced mild myocardial injury. Both variants caused fulminant pancreatitis with nearly complete necrosis of the exocrine pancreas. CBV3 RNA was identified by PCR in the myocardium of CBV3-W-infected mice until the end of the follow-up period of 14 days. Moreover, semiquantitative results were obtained when the PCR/hybridization results were analyzed by a phosphor imaging system. Immunohistochemistry and in situ hybridization from formaldehyde-fixed, paraffin-embedded specimens were highly similar in detecting viral components during the early stages of the myocardial injury. The results indicate that: (i) direct viral damage plays an essential role in acute murine CBV3-induced myocarditis, (ii) PCR appears a useful and sensitive diagnostic method in acute myocarditis, and (iii) immunohistochemistry as a specific and relatively rapid method might be practicable also in studying the early stages of acute myocarditis from archival clinical material.