Antiviral Resistance Genotyping

Varicella-zoster virus (VZV) anti-viral resistance genotyping.

Lesion swab 1 mL (0.5 mL minimum), vesicular fluid 1 mL (0.5 mL minimum), CSF 1mL mL (0.5 mL minimum ), whole blood 1 mL (0.5 mL minimum), or plasma 1 mL (0.5 mL minimum). Viral cultures 1 mL (0.5 mL minimum) may also be sent. Minimum volume will not allow repeat testing of samples with indeterminate results. Specimens must be confirmed to be VZV PCR positive before sending.

For lesion swabs, place swabs in 2-3 mL of viral transport medium (VTM) for a minimum of 1 hour and then remove the swab. For vesicular fluid, aspirate fluid from fresh unbroken vesicle and mix with at least 200 µL VTM. For plasma, collect blood in plasma preparation tube (PPT) or K2EDTA tube (plastic; lavender or pink top). Do not use heparin as an anti-coagulant. Centrifuge the tube at room temperature at 1,100 RCF for 10-15 min to separate the blood. Aliquot plasma into separate tube. Collect CSF in a dry tube subject to classic conditions for carrying out lumbar punctures. For viral cultures, collect infected cells and media.

Do not freeze whole blood; store and ship refrigerated within 48h of sample collection. Plasma, CSF, lesion swabs and fluid specimens may be stored and shipped refrigerated to NML within 48h of sample collection or must be stored and shipped frozen. Viral cultures must be stored frozen at all times and shipped on dry ice.

Shipping of specimens shall be done by a TDG certified individual in accordance with TDG regulations. For additional information regarding classification of specimens for the purposes of shipping, consult either Part 2 Appendix 3 of the TDG Regulations or section 3.6.2 of the IATA Dangerous Goods Regulations as applicable.

Suspected anti-viral resistant varicella-zoster virus, characterized by no improvement (or relapse) in lesions. Drug resistant VZV is more commonly isolated from immunocompromised patients. (1).

Results of VZV PCR including viral load copy number. Include date of VZV vaccination and date of rash onset. Completed “Sexually Transmitted and Opportunistic Infections ” requisition form including sender lab name, address and telephone number, patient identifier, date of birth or age and sex, specimen reference #, type of specimen, date collected, test requested, and any other relevant clinical information.

SPECIAL REQUEST ONLY. Contact the laboratory prior to sending specimens. The specimen should be positive for VZV DNA and results included with the requisition form.

Regions of the polymerase (ORF28) (3) and the thymidine kinase (ORF36) that include known acyclovir and derivative anti-viral resistant mutations are amplified by PCR and sequenced by Sanger sequencing. Sequence data is analysed and compared to wild-type reference sequences and mutations and/or frameshifts are identified. The VZV database of known mutations is limited and based on published results (1,2). Testing is performed, in part, using a lab-developed test which has not been fully validated/verified.

Please note that no phenotypic assays are performed. Interpret results with caution as this assay is for research purposes only.

Testing is performed, in whole or in part, using a “Research Use Only” testing kit which has not been fully validated/verified.

10 calendar days. STAT samples may be considered under special circumstances. Please contact lab prior to sending specimens.

1. Sauerbrei A. Varicella-zoster virus infections - antiviral therapy and diagnosis. GMS Infect Dis. 2016 Feb 17;4:Doc01. doi: 10.3205/id000019. PMID: 30671315; PMCID: PMC6301744.
2. Andrei G, Topalis D, Fiten P, McGuigan C, Balzarini J, Opdenakker G, Snoeck R. In vitro-selected drug-resistant varicella-zoster virus mutants in the thymidine kinase and DNA polymerase genes yield novel phenotype-genotype associations and highlight differences between antiherpesvirus drugs. J Virol. 2012 Mar;86(5):2641-52. doi: 10.1128/JVI.06620-11. Epub 2011 Dec 21. PMID: 22190713; PMCID: PMC3302250.
3. Perrier M, Désiré N, Deback C, Agut H, Boutolleau D, Burrel S. Complementary assays for monitoring susceptibility of varicella-zoster virus resistance to antivirals. J Virol Methods. 2016 Jul;233:10-4. doi: 10.1016/j.jviromet.2016.03.006. Epub 2016 Mar 16. PMID: 26994966.