Mature glycoprotein g presents high performance in diagnosing herpes simplex virus type 2 infection in sera of different tanzanian cohorts

Abstract

Herpes simplex virus type 2 (HSV-2) is a common sexually transmitted infection in sub-Saharan Africa. Glycoprotein G (gG) of HSV-2 elicits a type-specific antibody response and is widely used for serodiagnosis. gG is cleaved into a secreted portion (sgG-2) and a highly O-glycosylated mature portion (mgG-2). The performances of these two native immunosorbent purified antigens were compared in an enzyme-linked immunosorbent assay (ELISA) format with a commercially available assay (FOCUS2) using sera from blood donors (n = 194) and individuals (n = 198) with genital ulcer disease (GUD) from Tanzania. Discordant results were resolved by Western blotting. The HSV-2 seroprevalence for blood donors was estimated as 42%, and that for the GUD cohort was estimated as 78%. The prevalence increased significantly with age for both cohorts and was higher among human immunodeficiency virus (HIV)-positive individuals than among HIV-negative subjects. In the GUD cohort with a high HSV-2 prevalence, all three assays showed statistically similar performances, with sensitivities between 97% and 99% and specificities in the range of 86% to 91%. In contrast, among blood donors with a lower seroprevalence, the mgG-2-based ELISA presented significantly higher specificity (97%) than the sgG-2 ELISA (89%) and FOCUS2 (74%). Overall, the mgG-2 ELISA gave a high performance, with negative and positive predictive values of 96% for blood donors and a negative predictive value of 95% and a positive predictive value of 97% for the GUD cohort. We conclude that native purified mgG-2 showed the highest accuracy for detection of HSV-2 in patient sera from Tanzania and is therefore suitable for seroprevalence studies as well as in clinical settings.

FIG. 1.

Performance of sgG-2 and mgG-2 ELISAs presented as ROC plots for blood donors (A) and the GUD cohort (B). Cutoff values of control serum (CS) plus 0.1 to 0.6 OD units by incremental steps of 0.02 are plotted for both cohorts. For mgG-2 ELISA in the GUD cohort, plots representing CS plus 0.7, 0.8, 0.9, and 1.0 OD unit are plotted as well. The plots corresponding to CS plus 0.35 OD unit used as cutoff values are indicated with asterisks.

FIG. 2.

Age-stratified HSV-2 seroprevalences for blood donors and patients with GUD (A) and HSV-2 prevalences related to gender and HIV status in the GUD cohort (B). pos, positive; neg, negative.