Parvovirus B19 Myocarditis: The Utility of Viral Load Assessment in Determining the Significance of a Virus Positive Biopsy in South Africa

Background/Objectives Parvovirus B19 (PVB19) is the most frequently detected virus in endomyocardial biopsy (EMB) specimens of patients with acute myocarditis in both the developed world and South Africa. Its pathogenic role, however, remains debated as it is also commonly detected in hearts of patients with idiopathic dilated cardiomyopathy and cohorts of patients undergoing cardiac surgery and post-mortem cohorts without histological evidence of myocarditis. We sought to investigate the incremental diagnostic role of PVB19 viral load on EMB in a local cohort of patients with confirmed myocarditis. Methods This is a retrospective cross-sectional study. Consecutive adults presenting to a single tertiary centre in South Africa between August 2017 and January 2022 with clinically suspected acute myocarditis who had undergone both cardiac magnetic resonance imaging (CMR) and EMB, and had PVB19 detected by polymerase chain reaction (PCR) in EMB specimens, were included. Results Forty-nine patients with clinically suspected myocarditis had PVB19 detected on EMB specimens. Acute myocarditis was confirmed by CMR and/or EMB in 39 patients. The median high sensitivity troponin T (295.0ng/L vs 57.5ng/L, p = 0.035) and PVB19 viral load (483copies/ml vs 226copies/ml, p = 0.02) were significantly higher in patients with confirmed acute myocarditis compared to those without. The optimal PVB19 viral load threshold to determine clinical significance in the local population was 316copies/ml. Conclusions The mere presence of PVB19 in EMB specimens of patients with clinically suspected myocarditis appears to be insufficient for proving its causal role in acute myocarditis in South Africa. However, the presence of high viral copies may be used to inform the clinical relevance of a positive PVB19 EMB result.