Loss of maternally derived human herpesvirus 7 immunity and natural infection in Argentinian infants

Human herpes virus-7 (HHV-7) infection is widespread throughout the world. No data are available in Argentina about loss of maternally-derived HHV-7 immunity and natural infection.The objective of this study was to characterize the time when children lose maternal antibodies and become susceptible to natural infection.Sera from 39 pregnant women and 207 infants between 2 and 29 months of age were tested. Determination of IgG antibodies was made by indirect immunofluorescence.The seropositive ratio fell in the 2-4 month group (15% seropositive) and increased between 5 months (47% seropositive) and 23 months (67%). Geometric mean titers (GMT) of the infants aged 2-4 months (GMT = 60) were statistically different (p < 0.0001, Student's t-test) to those from the group of pregnant women (GMT = 83) and those from the other infant groups (p < 0.001, least significant difference (LSD) test). The GMT of the groups between 5 and 23 months did not show significant differences whereas those of infants between 24 and 29 months (GMT = 179, 79% seropositive) were different from all the groups studied (p < 0.0001, LSD test).This study shows a significant association between the loss of passive HHV-7 antibody and age. HHV-7 enters the susceptible population at 5 months, leading to the high prevalence of antibodies between 24 and 29 months of age. This study also shows that natural infection by HHV-7 in children during their first years of life follows the infection pattern found in developing countries.