Use of immunoglobulin G antibody avidity for differentiation of primary human herpesvirus 6 and 7 infections

Abstract

A human herpesvirus 7 (HHV-7) indirect immunofluorescence antibody avidity test was developed and used with an existing human herpesvirus 6 (HHV-6) antibody avidity test to detect and distinguish low-avidity antibodies to HHV-6 and HHV-7 and hence the respective primary infections. With sera from 269 British children aged 0 to 179 weeks, the tests showed that most (10 of 98 serum samples [13%]) HHV-6 low-avidity antibody was found in the first year of life, whereas for HHV-7, most (18 of 101 serum samples [20%]) HHV-7 low-avidity antibody was found in the second year of life. Five children had low-avidity antibodies to both viruses. Of nine Japanese children with previously serologically proven primary HHV-6 or HHV-7 infections, eight had low-avidity antibody only to the relevant virus, but one child had low-avidity antibodies to HHV-6 and HHV-7. The avidity tests were applied to five British children and further proof of viral infection was sought by the detection of specific DNA in serum or plasma, and saliva or cerebrospinal fluid. In two children who had low-avidity antibody to HHV-7 but who were seronegative for HHV-6, only HHV-7 was found. Both viruses were detected in one child with low-avidity HHV-7 antibody and high-avidity HHV-6 antibody. In two children with low-avidity antibodies to both viruses, HHV-6 and HHV-7 DNAs were found, confirming dual primary infections and excluding antibody cross-reactivity.

FIG. 1

Comparison of the change with age of the geometric mean titers of IgG antibodies to HHV-6 and HHV-7 in children. Geometric mean titers for HHV-6 (■) and HHV-7 (○) were calculated for 20-week age intervals from birth to 179 weeks. When the titer was <10 it was given a nominal value of 5. Bars represent the mean ± twice the standard error of the mean. The numbers of serum samples tested in each group were as follows: 0 to 19 weeks, 26; 20 to 39 weeks, 36; 40 to 59 weeks, 36; 60 to 79 weeks, 35; 80 to 99 weeks, 31; 100 to 119 weeks, 35; 120 to 139 weeks, 27; 140 to 159 weeks, 24; 160 to 179 weeks, 19.