Seroepidemiology of the human polyomavirus JC in a cohort of Italian infants

BACKGROUND: JC virus (JCV) is a widespread member of the Polyomaviridae family. Following the primary infection, that occurs asymptomatically during childhood, JCV persists as latent infection in the host. In patients with impaired immune function, JCV can reactivate and induce Progressive Multifocal Leukoencephalopathy (PML), a demyelinating disease of the Central Nervous System (CNS). The JCV seroprevalence between one and three years of age ranges from 11% to 16%, but the age of viral exposure has not been yet characterized. This study was conducted to defining the kinetic of maternal antibodies against JCV in Italian infants and to dating the viral primary infection. METHODS: an home made indirect Enzyme Linked Immunosorbent Assay (ELISA) was employed, using JCV Viral Protein 1-GST fusion protein to test for the presence of IgG to JCV in serum samples taken from 435 Italian infants. Samples were collected at different age of the children, from one day up to three years and clustered in 9 age-groups, for a total of 817 sera. The cut-off point of the ELISA test was determined in each assay by the mean OD reading of the negative controls which were added to standard deviation and multiplied three times. Serum from a PML patient was used as positive control. The JCV antibody prevalence was calculated for each group; for the longitudinal analysis, generalized estimating equations techniques with the use of spline functions were applied to estimate possible non linear effects of time on the antibodies kinetics. RESULTS: JCV IgG were detected in 49.5 %, and in 59.7% of the newborns within the first and the second month of life, respectively. The prevalence increased during the time, up to 69.8% and 82.7% after 12 and 24 months, respectively. Longitudinal analysis of antibody amounts in the sera collected from one day till three years of life indicated that the IgG kinetic grows with trends statistically significant (p=0.044). CONCLUSIONS: A sizeable percentage of Italian infants was subjected to the JCV primary infection within two years of life. The age-specific JCV seroprevalence was higher than previous published serosurveys. However, so far just few data on the JCV seroepidemiology of the population up to three years are available and derived from cohorts limited in size. Additionally, no other JCV serosurveys focused on Italian infants have been so far published.