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Chapter 71 : Varicella-Zoster Virus
Laboratory diagnosis of varicella-zoster virus (VZV) infection requires the identification of the virus or one of its products in skin lesions, tissues, or fluids from the patient. Techniques include isolation of the virus in tissue culture, direct immunofluorescent staining of cells obtained from lesions, and detection of the virus genome by techniques based on PCR. Vesicular fluids, crusts that have been ground in water, or skin lesion sections can be examined by electron microscopy (EM). The authors had experience of successful identification and typing of VZV strains from environmental swabs. Recent studies indicate that while multiple polymorphisms were identified between vaccine and wild-type strains, detection of the sequence polymorphism at genome position 106262 is the most reliable method for discriminating the vaccine strain from wild-type VZV. Perhaps the most important concern in the use of PCR is the quality of the template to be amplified. Serologic testing is most often requested for determining susceptibility to VZV in outbreak settings, but on occasion it is needed for diagnosis. Assay formats used for simple determination of VZV serostatus include enzyme-linked immunosorbent assay (ELISA), membrane fluorescence, and latex bead agglutination. Each of these test formats has limitations, which are discussed in this chapter. The authors recently documented cases of varicella in health care workers who were incorrectly identified as VZV seropositive by the latex bead agglutination method. Despite VZV immunoglobulin (VZIG) prophylaxis, approximately two-thirds of infants exposed to maternal varicella around the time of delivery will become infected.
Key Concept Ranking
- Restriction Fragment Length Polymorphism