Laboratory diagnosis

The clinical presentations of varicella or zoster are so characteristic that laboratory confirmation is rarely required only for a typical presentation, particularly in the immunocopmromised , and for distinguishing between HSV infection and herpes zoster .

a. Cytology - smears of scrapings of the base of the lesions will reveal characteristic multinucleate giant cells, also known as Tzanck cells . However this technique will not distinguish between HSV and VZV infection .

b. Electron microscopy - herpesvirus particles can be in fluid taken from the early vesicles of either varicella or zoster . This technique cannot distinguish between HSV and VZV.

c. Immunofluorescence cytology - smears of the base of lesions can be examined by Immunofluorescence cytology, as in the case for HSV . This technique is more sensitive than EM but is more labour intensive and requires greater technical expertise .

d. Molecular Methods - PCR assays for VZV are available and have been reported to be of use in the diagnosis of VZV meningoencephalitis from CSF specimens .

B.virus isolation

THis remains the definitive method for diagnosing VZV infections . Human fibrolasts are used in most laboratories .

Vesicle fluid and scrapings from the base of fresh lesions are the most suitable specimens. Virus can rarely be recovered from crusted lesions .

Biopsy material can also be cultured .

The CPE produced by VZV is so characteristic that most laboratories do not undertake further identification of the isolates .

Immunofluorescene of the cell sheet by monoclonal antibodies is the method of choice for identification.

virus isolation for VZV is rarely carried out because of the long length of time required for a result to be available .