Rapid diagnosis in varicella and herpes zoster: re-evaluation of direct smear (Tzanck test) and electron microscopy including colloidal gold immuno-electron microscopy in comparison with virus isolation.

The Tzanck test and electron microscopy with the technique of colloidal gold labelling in varicella-zoster virus (VZV) infections were compared with virus isolation in 54 patients with clinically suspected varicella or herpes zoster infection. The Tzanck test and direct electron microscopy can determine whether or not an eruption is herpetic but cannot distinguish between herpes simplex virus (HSV) and VZV infection. However, colloidal gold immuno-electron microscopy, using monoclonal antibodies against HSV and anti-VZV IgG, can distinguish between these two herpes viruses. This achieves the same specificity as virus isolation followed by virus neutralization or virus typing using immunofluorescence techniques. The Tzanck test was positive in 91%, virus isolation, under optimal conditions of sampling and transportation, in 80%, direct electron microscopy (negative staining) in 80%, and colloidal gold immuno-electron microscopy after a virus concentration procedure in 95% of the cases. The colloidal gold technique offers a rapid diagnosis in patients with suspected VZV infection.