Laboratory Diagnosis - Varicella Zoster Virus Infections

Laboratory Diagnosis

In almost all the cases, diagnosis of chickenpox and herpes zoster is always clinical.

◗ Specimens

These include skin lesion specimens, respiratory secretions, or organ biopsy.

◗ Direct antigen detection

Direct fluorescent antibody test employing antibodies against viral membrane antigen (fluorescent antibody to membrane antigen; FAMA) is used to detect membrane antigen of the virus directly in the skin scrapings and biopsy specimens. The coun-tercurrent immunoelectrophoresis using zoster immune serum is also used to detect antigen directly in the vesicular fluid.

◗ Isolation of the virus

Specimens from buccal or skin lesions collected during early stage of the disease are cultured on human amnion, human fibroblast, and HeLa or Vero cells. The VZV produces a CPE similar to that of HSV, but is less conspicuous and takes a long time to develop.

◗ Serodiagnosis

Both indirect fluorescent antibody and enzyme-linked immu-nosorbent assay are employed to detect serum antibodies against VZV. These tests are useful mainly for epidemiological studies rather than for diagnosis of individual cases.

◗ Other tests

Histology: The Tzanck smear is useful to detect Cowdry typeA intranuclear inclusions and syncytia in VZV-infected cells.