Background
Herpes simplex viruses exist as two major serotypes, type 1 (HSV-1) and type 2 (HSV-2). Determination of type, either HSV-1 or HSV-2, is important in accurate diagnosis and clinical control of transmission. Several tests are available for typing HSV, including a monoclonal antibody specific for glycoprotein G and several PCR assays.
Findings
A clinical isolate was identified as herpes simplex virus, but tested negative for both HSV-1 and HSV-2 antigens using type-specific monoclonal antibody assays. The isolate was determined to be HSV-1 by PCR analysis. A mutation which likely caused the monoclonal antibody non-reactivity was found in glycoprotein G. Phylogenetic analysis revealed two groups of HSV, one with the mutation and one without. Three population studies examining mutations in HSV-1 glycoprotein G were analyzed by chi-squared test. To this point, the epitope which the monoclonal antibody recognizes was only found in HSV-1 isolates from human European populations (p < 0.0001).
Conclusions
These findings suggest that the PCR-based methods for HSV typing may be more useful than the standard monoclonal antibody test in areas of the world where the variant in glycoprotein G is more prevalent.
Findings
Herpes simplex viruses exist as two major serotypes, type 1 (HSV-1) and type 2 (HSV-2). Determination of type, either HSV-1 or HSV-2, is important in accurate diagnosis and clinical control of transmission. Tests which can determine HSV type include viral antigen tests, serological tests of human antibodies and PCR. The importance of glycoprotein G as the test analyte is emphasized by the 2002 STD Treatment Guidelines from the CDC: “Accurate type-specific assays for HSV antibodies must be based on the HSV-specific glycoprotein G2 for the diagnosis of infection with HSV-2 and glycoprotein G1 for diagnosis of infection with HSV-1.”.
A clinical sample of a herpes simplex virus, designated Y3369 was isolated and proved refractory to typing. The isolate was obtained from an infected genital tract of a 48-year-old female patient. It was submitted to Richards Laboratories, Inc., Pleasant Grove, Utah, USA for diagnostic workup. The sample was incubated overnight, and then stained for virus-infected cells using a type-common polyclonal primary antibody and visualized by the immunoperoxidase technique using a rapid culture method. The culture showed an abundance of cells positive for antibody labeling and had HSV-typical cytopathic effects, confirming the presence of HSV in the specimen (results not shown).
The Y3369 isolate was then tested using the Wampole type-specific viral antigen test for HSV glycoprotein G. A viral stock culture was generated by inoculation of a portion of the rapid culture isolate into a culture of MV1Lu cells (mink lung, ATCC CCL-64). The specimen was also incubated in C1008 cells (Vero subline, ATCC CRL-1586) and subjected to similar serotypic analysis by staining with virus-specific monoclonal antibodies (mAbs) against HSV type 1 and type 2. These tests failed to yield a positive identification of the isolate as either HSV-1 or HSV-2 using type-specific mAb assays (Wampole Laboratories). The immunofluorescence result was negative against both reagent antisera in MV1Lu cells. The virus was also untypable in C1008 cells (not shown). The laboratory strains HSV-1 McIntyre and HSV-2 strain 333 were tested with mAb reagents and expected monotypic results were observed in these controls.