Serological evidence of Merkel cell polyomavirus primary infections in childhood

Background: Merkel cell polyomavirus (MCPyV) was identified newly (2008) and is believed to be an etiologic factor of Merkel cell carcinoma (MCC). Recent molecular and serological data suggest that MCPyV infection is common in the general population. Objectives: The aim of this study was to investigate the age of primary exposure to MCPyV. Study design: A MCPyV-IgG EIA was developed using the MCPyV major capsid protein VP1 expressed and self-assembled into virus-like particles (VLPs) in insect cells. The assay was used to detect serum IgG antibodies in two groups of children. Group 1 comprised paired and 5-8 year follow-up sera from 217 children (3-13 years) with acute lower respiratory tract infection. Group 2 comprised sera from 158 children (1-4 years) with otitis media; 86 children underwent adenoidectomy and 72 did not, whereafter follow-up sera were obtained 3 years later. Result: The prevalence of MCPyV-IgG was 9% at 1-4 years, and increased to 35% at 4-13 years among subjects from Group 1, with a 33% seroconversion rate during 5-8 years. Among Group 2, the seroconversion rate was 16% during 3 years. The IgG prevalence at 4-7 years as well as the IgG levels showed an apparent gender difference, with male preponderance prevailing among the children without adenoidectomy. Conclusion: MCPyV primary infections occur ubiquitously in childhood, and the first exposure takes place at young age. The serology showed no evidence for a causative role of MCPyV in lower respiratory tract infection manifesting as acute wheezing, but was compatible with the notion of MCPyV persistence in tonsils.