CLINICAL VARICELLA-ZOSTER VIRUS ISOLATE WITH A MUTATION IN THE 3B3 MONOCLONAL ANTIBODY EPITOPE OF GLYCOPROTEIN E

*G.A. Tipples (1), G.M. Stephens (2), R. Reynolds (3), C. Sherlock (2), M. Bowler (2), B. Hoy (4), D. Cook (4), M. Cossitt (1) and R. Garceau (5).
(1) Viral Exanthemata, National Microbiology Laboratory, Winnipeg, Manitoba, (2) UBC Virology and Reference Laboratory, St. Paul's Hospital, Vancouver, BC, (3) UBC Department of Medicine, Division of Infectious Diseases, Vancouver Hospital, Vancouver, BC, (4) BC Centre for Disease Control, Vancouver, BC, and (5) L'Hôpital Régional Dr GL Dumont, Moncton, New Brunswick, Canada

The objective of our study was to laboratory confirm an unusual clinical zoster case, characterize the varicella-zoster virus (VZV) isolate, and determine the frequency of detection of this unusual genotype in a collection of 59 clinical VZV isolates.

A swab of facial vesicles was obtained from a patient exhibiting clinical zoster. Typical VZV cytopathogenic effect (CPE) was seen after 9 days growth in HFF cells. The virus could not be subsequently propagated in Vero, MRC-5, HEp-2 or RMK cells. Enveloped herpes virus was detected by electron microscopy (EM). However, immunofluorescence (IF) staining with monoclonal antibodies (MAb) to CMV, HSV-1 and 2 and VZV (3B3) were all negative. PCR amplification of the VZV ORF68 gene (encodes glycoprotein E, gE) produced the expected 1872bp amplicon. Subsequent DNA sequencing of this amplicon indicated this sequence was identical to the VZV ORF68 Dumas reference strain sequence in GenBank with the exception of a G448A nucleotide mutation (D150N amino acid substitution) in the 3B3 epitope of gE. The G448A mutation was not detected by differential PCR in any of the 59 clinical VZV isolates tested.

Clinical presentation, CPE in cell culture and EM indicated probable VZV infection. Negative 3B3 VZV MAb IF results were surprising and stimulated further investigation. VZV was confirmed by PCR and sequence analysis. The G448A mutation detected in this clinical isolate was identical to a mutation in the 3B3 epitope previously reported by Santos et al (Virology 1998;249:21-31). However, this mutant 3B3 epitope genotype appears to be quite rare. This study illustrates potential limitations for using 3B3 Mab for lab confirmation of VZV.

Corresponding Author: Graham A. Tipples, PhD, Head of Viral Exanthemata,
National Microbiology Laboratory, Health Canada, 1015 Arlington Street,
Winnipeg, Manitoba, R3E 3R2, Canada