Compartmentalization of acyclovir-resistant varicella zoster virus: implications for sampling in molecular diagnostics

Heterogeneity and viral replication fitness of HSV-1 clinical isolates with mutations in the thymidine kinase and DNA polymerase

BACKGROUND

Prolonged antiviral therapy in immunocompromised individuals can result in the emergence of (multi)drug-resistant herpes simplex virus 1 (HSV-1) infections, forming a therapeutic challenge.

OBJECTIVES

To evaluate spatial and temporal differences in drug resistance of HSV-1 samples from a HSCT recipient and to determine the effect of resistance mutations on viral replication fitness.

PATIENTS AND METHODS

Five HSV-1 isolates were recovered from a HSCT recipient who suffered from persistent HSV-1 lesions, consecutively treated with aciclovir, foscarnet, cidofovir and a combination of ganciclovir and cidofovir. Spatial and temporal differences in HSV-1 drug resistance were evaluated genotypically [Sanger sequencing and next-generation sequencing (NGS) of the viral thymidine kinase (TK) and DNA polymerase (DP)] and phenotypically (plaque reduction assay). Viral replication fitness was determined by dual infection competition assays.

RESULTS

Rapid evolution to aciclovir and foscarnet resistance was observed due to acquisition of TK (A189V and R222H) and DP (L778M and L802F) mutations. Virus isolates showed heterogeneous populations, spatial virus compartmentalization and minor viral variants in three out of five isolates (detectable by NGS but not by Sanger sequencing). Mutations in the TK and DP genes did not alter replication fitness without drug pressure. TK and/or DP mutants influenced replication fitness under antiviral pressure and showed increased fitness under pressure of the drug they showed resistance to.

CONCLUSIONS

The use of NGS and dual infection competition assays revealed rapid evolution of HSV-1 drug resistance in a HSCT recipient with spatial and temporal compartmentalization of viral variants that had altered replication fitness under antiviral pressure.

Advances and Perspectives in the Management of Varicella-Zoster Virus Infections

Varicella-zoster virus (VZV), a common and ubiquitous human-restricted pathogen, causes a primary infection (varicella or chickenpox) followed by establishment of latency in sensory ganglia. The virus can reactivate, causing herpes zoster (HZ, shingles) and leading to significant morbidity but rarely mortality, although in immunocompromised hosts, VZV can cause severe disseminated and occasionally fatal disease. We discuss VZV diseases and the decrease in their incidence due to the introduction of live-attenuated vaccines to prevent varicella or HZ. We also focus on acyclovir, valacyclovir, and famciclovir (FDA approved drugs to treat VZV infections), brivudine (used in some European countries) and amenamevir (a helicase-primase inhibitor, approved in Japan) that augur the beginning of a new era of anti-VZV therapy. Valnivudine hydrochloride (FV-100) and valomaciclovir stearate (in advanced stage of development) and several new molecules potentially good as anti-VZV candidates described during the last year are examined. We reflect on the role of antiviral agents in the treatment of VZV-associated diseases, as a large percentage of the at-risk population is not immunized, and on the limitations of currently FDA-approved anti-VZV drugs. Their low efficacy in controlling HZ pain and post-herpetic neuralgia development, and the need of multiple dosing regimens requiring daily dose adaptation for patients with renal failure urges the development of novel anti-VZV drugs.

Antiviral resistance in herpes simplex virus and varicella-zoster virus infections: diagnosis and management

PURPOSE OF REVIEW

Aciclovir (ACV) is the first-line drug for the management of herpes simplex virus (HSV) and varicella-zoster virus (VZV) infections. Long-term administration of ACV for the treatment of severe infections in immunocompromised patients can lead to the development of drug resistance. Furthermore, the emergence of isolates resistant to ACV is increasingly recognized in immunocompetent individuals with herpetic keratitis. This review describes the mechanisms involved in drug resistance for HSV and VZV, the laboratory diagnosis and management of patients with infections refractory to ACV therapy.

RECENT FINDINGS

Genotypic testing is more frequently performed for the diagnosis of infections caused by drug-resistant HSV or VZV isolates. Molecular biology-based systems for the generation of recombinant viruses have been developed to link unknown mutations with their drug phenotypes. Fast and sensitive methods based on next-generation sequencing will improve the detection of heterogeneous viral populations of drug-resistant viruses and their temporal changes during antiviral therapy, which could allow better patient management. Novel promising compounds acting on targets that differ from the viral DNA polymerase are under clinical development.

SUMMARY

Antiviral drug resistance monitoring for HSV and VZV is required for a rational use of antiviral therapy in high-risk populations.

Molecular method development and establishment of a database for clinical and epidemiological herpes simplex virus 1 strain comparisons

Previous methods of herpes simplex virus 1 (HSV-1) genotype analysis have lacked sufficient discriminatory power for strain analysis within genotypes. The hypervariable reiterative repeat regions in the US1 and US12 introns, known as ReIV, were targeted for strain comparison. PCR methods for these extremely GC-rich target regions were optimized to give reproducible amplicons that were visualized by capillary electrophoresis relative to size standards. Analysis of the size, shape, and pattern of the resulting signatures enabled strain discrimination. Primary clinical specimens were used to develop the assay and the analysis algorithm. A blinded clinical study of 147 in-state and 51 out-of-state samples, including matched specimen-isolate pairs, was then performed. All primary clinical samples had been collected between 2004 and 2011 for viral diagnosis and previously found to be positive for HSV-1 by real-time PCR. The combined database contained patterns from 264 samples collected from 199 patients with a total of 176 unique signatures, none of which were dominant in the population. Matches between the signatures of the more than 50 specimen-isolate pairs were always seen. Signatures also matched across multiple samples collected from individual patients (six such cases), as well as some additional signature matches where epidemiological links were likely. Results were reproducible on repeat testing of individual specimens, even after months in frozen storage. The protocol has multiple potential clinical and public health uses.

Acyclovir-resistant varicella-zoster virus keratitis in an immunocompetent patient

Varicella-zoster virus (VZV) resistance to acyclovir (ACV) has only been reported in rare cases of immunocompromised patients. We report the first case of an immunocompetent patient with ACV-resistant VZV keratitis associated with a nucleotide deletion in the VZV thymidine kinase gene, leading to production of a truncated protein.

Persistence and antiviral resistance of varicella zoster virus in hematological patients

BACKGROUND

Varicella zoster virus (VZV) infections are a relevant cause of morbidity and mortality in hematological patients and especially in hematopoietic stem cell transplant (HSCT) recipients. The present study aimed to investigate the prevalence and clinical significance of viral persistence and antiviral resistance by systematically analyzing all episodes of VZV diagnosed in our laboratory in pediatric and adult hematological patients between 2007 and 2010.

METHODS

Patient charts were reviewed to document patient and disease characteristics. VZV loads were determined in all available clinical samples from the day of diagnosis and thereafter. Persistent VZV infection was defined as a VZV infection that lasted at least 7 days. Analysis of resistance was performed in all patients with persistent VZV infection by sequence analysis of viral thymidine kinase and DNA polymerase genes.

RESULTS

In total, 89 episodes occurred in 87 patients, of whom 65 were recipients of an allogeneic HSCT. Follow-up samples were available in 54 episodes. Persistent VZV was demonstrated in 32 of these episodes (59%). Complications occurred in 16 of the persistent episodes (50%) vs 2 of 22 nonpersistent episodes (9%). Mutations possibly associated with resistance were found in 27% of patients with persistent VZV, including patients with treatment-unresponsive dermatomal zoster that progressed to severe retinal or cerebral infection.

CONCLUSIONS

In hematological patients, VZV-related complications occur frequently, especially in persistent infections. Antiviral resistance is a relevant factor in persistent infections and needs to be investigated in various affected body sites, especially when clinical suspicion of treatment failure arises.

Nonneoplastic mucocutaneous lesions in organ transplant recipients

Nonneoplastic mucocutaneous lesions are frequent in organ transplant recipients. Many of them are caused by a direct toxicity of immunosuppressive drugs, in particular glucocorticoids and cyclosporine. The effects of these agents are dose- and time-dependent. Glucocorticoids can cause acne, Cushingoid appearance, irregular purpuric areas, friable skin, and wide and violaceous stripes. Cyclosporine can cause hypertrichosis, pilosebaceous lesions, and gum hypertrophy. Patients with esthetic changes may show poor adherence to treatment with these immunosuppressive agents that may lead to progressive graft dysfunction. Apart from this direct toxicity, vigorous immunosuppression may render the transplant recipients more susceptible to mucocutaneous infections. Fungal infection, viral warts, and bacterial folliculitis are the most frequent types of mucocutaneous infection. Some fungal infections, such as oral candidiasis and pityriasis versicolor, are relatively trivial, but other mycotic infections can cause severe or disfigurating lesions. Among viral infections, warts and condylomata caused by human papilloma virus are frequent and may favor the development of nonmelanoma skin cancer. Bacterial infections are usually trivial in the early period after transplantation, being represented almost exclusively by folliculitis. However, subcutaneous infections may cause a necrotizing fasciculitis which is a life-threatening disorder, usually sustained by polymicrobial pathogens.