Journal of Clinical Virology 40 (2007) 129–134 Detection and differentiation of wild-type and vaccine mutant varicella-zoster viruses using an Invader Plus ® method  Yi-Wei Tang a,b,∗ , Hatim T. Allawi c , Marlene DeLeon-Carnes d , Haijing Li a , Stephen P. Day c , D. Scott Schmid d a Department of Medicine, Vanderbilt University School of Medicine, Nashville, TN 37232, United States b Department of Pathology, Vanderbilt University School of Medicine, Nashville, TN 37232, United States c Third Wave Technologies, Inc., Madison, WI 53719, United States d National Center for Immunizations and Respiratory Diseases, Centers for Disease Control and Prevention, Atlanta, GA 30333, United States Received 16 March 2007; received in revised form 13 July 2007; accepted 18 July 2007 Abstract We report the use of a prototype Invader Plus ® method (Third Wave Technologies, Inc., Madison, WI) for the qualitative detection of varicella- zoster virus (VZV) and differentiation of wild-type and Oka vaccine VZV. The analytical sensitivity of the VZV Invader Plus reagents is at 10 copies per reaction. A total of 174 skin and mucous swab specimens were used to validate the assay’s performance. The sensitivity and specificity were 98.3% and 98.1%, respectively, in comparison to a PCR-EIA assay. A perfect 100% agreement was obtained when VZV wild-type and vaccine differentiation was performed on 54 VZV-positive swab specimens against an allele-specific FRET real-time assay. The Invader Plus method provides another reliable tool for qualitative detection of VZV and differentiation of wild-type and vaccine virus. © 2007 Elsevier B.V. All rights reserved. Keywords: Varicella-zoster virus; Invader Plus ® method; Oka varicella vaccine 1. Introduction Varicella-zoster virus (VZV) is the etiologic agent of chicken pox in childhood and can reactivate, particularly in elderly or immunocompromised persons, to cause shin- gles (Gnann and Whitley, 2002). VZV infections are usually benign, but occasionally result in severe disease, such as pneumonia, encephalitis, and congenital injury (Gnann and Whitley, 2002). With the advent of routine varicella immu- nization, the incidence of varicella has been dramatically reduced in the US; in addition, breakthrough disease in vac- cinated persons is usually highly modified, although patients with modified disease remain contagious. As a direct result,  The findings and conclusions in this report are those of the authors and do not necessarily represent the views of the funding agencies. ∗ Corresponding author at: Molecular Infectious Diseases Laboratory, 4605 TVC, Vanderbilt University Hospital, Tennessee 37232-5310, United States. Tel.: +1 615 322 2035; fax: +1 615 343 8420. E-mail address: yiwei.tang@vanderbilt.edu (Y.-W. Tang). physician diagnosis has become more difficult and less reli- able, and rapid laboratory diagnostics are urgently needed to distinguish VZV infections from other clinical conditions. A live attenuated Oka vaccine (V-Oka) strain was atten- uated more than 30 years ago (Takahashi et al., 1974) and extensive clinical trials have shown the VZV vaccine is safe and highly effective in both healthy and immunocompro- mised individuals (Gershon et al., 1986; White, 1997)a much higher dose vaccine formulation also prevents herpes zoster and postherpetic neuralgia in older adults (Oxman et al., 2005). However, vaccine-associated rash occurs in 4–7% of healthy individuals (White, 1997) and in up to 40% of leukemic vaccinees (Gershon et al., 1986). Since the vac- cine virus is less pathogenic and transmissible than wild-type virus, a timely detection of VZV and differentiation of vac- cine or wild-type may aid in the management of clinical disease. In addition to providing a definitive diagnosis for vaccine-modified varicella, laboratory confirmation of VZV infections is also useful for differentiation from other 1386-6532/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jcv.2007.07.007